# Exploring techno-functional properties, synergies, and challenges of pectins: A review

Ali Assifaoui, Gayane Hayrapetyan, Clémence Gallery, Guéba

Agoda-Tandjawa

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Ali Assifaoui, Gayane Hayrapetyan, Clémence Gallery, Guéba Agoda-Tandjawa. Exploring techno-functional properties, synergies, and challenges of pectins: A review. Carbohydrate Polymer Technologies and Applications, 2024, 7, pp.100496. 10.1016/j.carpta.2024.100496. hal-05143753

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# Exploring techno-functional properties, synergies, and challenges of pectins: A review

Ali Assifaoui<sup>a, *</sup>, Gayane Hayrapetyan<sup>a</sup>, Clémence Gallery<sup>b</sup>, Guéba Agoda-Tandjawa<sup>c, *</sup>

## ARTICLE INFO

### Keywords:

Pectins

Physicochemical mechanisms

Techno-functional properties

Synergies

Interactions

Applications

## ABSTRACT

In this review, various aspects of pectins (from raw materials to process-structure-function-applications of this multifunctional biomacromolecule) are discussed taking into consideration the interests of scientists, producers, formulators, including customers and market constraints. Research on pectins has been a subject of interest among many researchers, consequently, numerous articles were published in the past decade. However, there are still some controversial ideas and related challenges associated with this multifunctional polymer which need further clarification. To settle on each of them, the review is structured into four parts: (i) what is already known, (ii) mechanisms describing the physicochemical phenomena involved in pectin techno-functional properties, (iii) current and future challenges from multiple angles, and (iv) related market trends. The information disclosed in this review could be particularly useful for pectin producers allowing them to boost sustainable innovation and also for those seeking in-depth knowledge on different aspects of this versatile biopolymer. Additionally, this review will provide the reader with the tools which allow obtaining fundamental and applied knowledge on pectins.

## Introduction

After cellulose and starch, pectin is the third most abundant plant polysaccharide. This anionic water-soluble heteropolysaccharide is commercially extracted from industrial waste produced during fruit production, such as citrus peels and apple pomace (Georgiev, Ognyanov, Yanakieva, Kussovski & Kratchanova, 2013; Kumar & Chauhan, 2010; Kurita, Fujiwara & Yamazaki, 2008). Based on the plant source and the conditions of the extraction treatment, the yield, nature, and structure of the resulting pectins will be affected, thereby influencing their techno-functional properties. The use of pectins is rapidly increasing due to their unique physiological activity and versatile texturizing properties. Over the last decade (2010–2020), the demand for pectin in the market has grown rapidly. Several hydrocolloid market analysts have even suggested that pectin could replace several hydrocolloids that have been extensively used due to its significantly lower cost (Ciriminna, Fidalgo, Scurria, Ilharco & Pagliaro, 2022; Pagliaro, Ciriminna, Fidalgo, Delisi & Ilharco, 2016). In 2020, the global annual consumption of pectins was estimated to be approximately 70,000 tons, with a market value of at least $1.25 billion (Ciriminna et al., 2022; Khedmat, Izadi,

Mofid & Mojtahedi, 2020; Seisun & Zalesny, 2021). The pectin market is projected to grow at a 7.6% compound annual growth rate (CAGR) within the period 2020 and 2026 because of the growing demand from various industries (Banerjee et al., 2017; Ciriminna et al., 2022; Khedmat et al., 2020). The global hydrocolloid market indicates that the food and pharmaceutical sector serves as the primary customer segment for pectin, offering a diverse array of applications such as gelling, stabilizing, thickening, emulsifying, and colour-protecting agents, in addition to its role as a dietary fiber source. For food applications, pectin ingredients have found a place in a large range of processed food products from ice cream to vegan gummies, spreads remain its biggest application area. Not surprisingly, the ingredient remains popular in jams and fruit spreads space, a subcategory that accounts for roughly 80% of new spread launches (Cargill, 2022). Since pectin is a natural component of vegetables and fruits, it is a safe food additive (E440) with no determined limit of daily intake. Moreover, pectin is one of the few polysaccharides with biomedical activity, making it a promising candidate in medicine and drug delivery applications (Khedmat et al., 2020). Moreover, pectin has been renamed recently “a universal medicine” considering its broad physiological activities (Zaitseva, Khudyakov,

<footnote><sup>a</sup> Université Bourgogne Franche-Comté, Institut Agro, Université Bourgogne, INRAE, UMR PAM 1517, Dijon 21000, France</footnote>

<footnote><sup>b</sup> Department of Food Safety Quality & Regulatory, Cargill Analytical Chemistry Group EMEA, Carentan 50500, France</footnote>

<footnote><sup>c</sup> Centre of Expertise Texture, Cargill Starches Sweeteners & Texturizers, Carentan 50500, France</footnote>

<footnote>* Corresponding authors.</footnote>

<footnote>E-mail addresses: ali.assifaoui@u-bourgogne.fr (A. Assifaoui), gueba_agoda-tandjawa@cargill.com (G. Agoda-Tandjawa).</footnote>
Sergushkina, Solomina & Polezhaeva, 2020). Other properties related to the antibacterial activity of new citrus pectins (IntegroPectin®) have been also demonstrated (Ciriminna, Albanese, Meneguzzo & Pagliaro, 2021). It must be noted that pectins with “pharmaceutical grade” meeting standards for microbiological and chemical purity are sold at prices exceeding $1000/kg (Ciriminna et al., 2022). The scientific interest in pectins is evident from the substantial number of articles and reviews published in the last decade, with approximately 5000 articles and 180 reviews dedicated to pectins according to the current records from the Web of Science database (Fig. 1). From an industrial perspective, the use of pectins in various domains such as pharmaceutics, food, and cosmetics has led to the emergence of numerous final products. The significant demand for pectins is driven by advancements in extraction methods, modifications that enhance innovative functionalities, and the exploration of novel pectin sources. This valuable knowledge is achieved through a mutually beneficial collaboration between academics and industrialists. The industry relies on academic expertise to address challenges related to improving the quality and functionality of pectins and understanding the role of specific components in the process. On the other hand, academia views collaboration with industry as a means of securing funding and, more importantly, an opportunity to create and exchange knowledge from technical and scientific perspectives. This collaboration plays a vital role in sustainable innovation, process optimization, and the exploration of new routes for rational formulation.

Several interesting reviews and books on pectin have been recently published, highlighting the growing interest in this field (Assifaoui & Chambin, 2020; Cao et al., 2018; Li, Li et al., 2021; Reichembach & Lucia de Oliveira Petkowicz, 2021; Wang et al., 2019). However, there are still various controversial aspects that require further discussion. This review primarily focuses on the techno-functional properties of pectins and their interactions with other ingredients such as polysaccharides, proteins, lipids, volatiles, polyphenols, and surfactants, either as a single ingredient or in mixtures. These fundamental aspects hold significant value not only for pectin producers but also for scientists. Each point addressed in this review follows a structured approach. Firstly, we present the existing knowledge on the aforementioned aspects, providing background information and identifying problematic areas that were not clearly addressed in previous publications. Secondly, we describe and explain the mechanisms involved in the physicochemical phenomena associated with pectin with a particular focus on some

controversial aspects on pectin gelation mechanisms. Thirdly, we explore current and future challenges from multiple perspectives. Finally, we discuss market trends by considering available literature unlike previous review papers on pectins.

## Pectin structure and production

It is well-known that the functionalities of pectin depend on its structure, including the presence of functional groups. The structure and functional properties of pectin are significantly influenced by the extraction processes employed (Cui et al., 2021). In this review, although we will not extensively explore the details of extraction processes, we will offer a brief overview of pectin's structure and the commonly employed methods for extraction.

### Pectin structure

Pectin, a highly intricate polysaccharide, consists of a complex arrangement of up to eighteen different monosaccharides connected by twenty distinct linkages (Ropartz & Ralet, 2020; Thibault & Ralet, 2003). Its content, composition, and structure vary depending on factors such as botanical origin, tissue and cell types, cellular development stages, and specific locations within the cell wall (Voragen, Pilnik, Thibault, Axelos & Renard, 1995). Despite this complexity, pectin is generally recognized as a heteropolysaccharide rich in α-1,4-linked d-galacturonic acid (GalA). It can be categorized into four main regions: homogalacturonan (HG), rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and xylogalacturonan (XG). HG and RG-I are the major components, accounting for approximately 60–65% and 20–35% of the total pectin, respectively. The homogalacturonan backbone is linear, and certain GalA units may be methylated or acetylated. RG-I is generally considered to be branched GalA, while RG-II and XG are branched structures containing α-1,2-linked rhamnose (Rha) residues, sometimes substituted with β-1,4-galactan, branched arabinan, or arabinogalactan side chains (Fig. 2) (Willats, Knox & Mikkelsen, 2006). Recent research has shown that specific structural characteristics of pectin, such as the number of branches, length of terminal galactan residues attached to the RG-I domain, degree of esterification (DE), and unsaturated GalA derivatives, contribute to the enhanced anti-inflammatory and anti-proliferative activities of modified citrus

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** Number of publications over the last decade. Insets represent the number of publications dedicated to various pectin functions (such as gelling, film forming, emulsifying, etc.) and different topics related to pectin (extraction and interactions with other macromolecules). Data sourced from web science on the 14th of December 2023.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 2. Schematic representation of the conventional structure of pectin.</figcaption></figure>

pectin (Cao, Yang, Wang, Lu & Yue, 2020). DE is expressed as a percentage and represents the amount of esterified GalA compared to the total number of GalA acids present in the pectin molecule. The pectins extracted from fruits and vegetables are primarily high-methoxyl pectins (HMP) with a DE higher than 50%. Other macromolecular features, such as the degree of acetylation (DAC), blockiness (DB), and polymerization (DP), aid in pectin identification (Guillotin, Bakx, Boulenguer, Schols & Voragen, 2007; Ralet, Crépeau & Bonnin, 2008). Furthermore, the pectin's structure directly influences its gel-forming ability and emulsion stabilization properties (Voragen et al., 1995). The molecular polydispersity of the pectin makes the usual analyses on whole macromolecules not powerful enough to reveal all the structural details of pectin (Bonnin, Garnier & Ralet, 2014; Hellin, Ralet, Bonnin & Thibault, 2005; Morris & Ralet, 2012; Ralet, Lerouge & Quemener, 2009).

## Pectin production and modification

Although pectins can be extracted from many plants, the main industrial or conventional sources are limited to citrus peel and apple pomace. The most cost-effective conventional sources of pectins are lemon (48%), lime (26%), and orange peels (11%) (Da Silva & Rao, 2006; Pagliaro et al., 2016). Citrus fruits are grown in over 140 countries worldwide and the total citrus production was estimated to be 144 million tons in 2019 – 2020 (Ladaniya, 2023). Additionally, other less common sources for pectin extraction have been extensively studied and found to contain pectin with desirable properties. The unconventional raw materials are the following: mango peels (Jamsazzadeh Kermani et al., 2014; Rehman, Salariya, Habib & Shah, 2004), banana peels (Swamy & Muthukumarappan, 2017), grape pomace (Colodel, Vriesmann, Teófilo & de Oliveira Petkowicz, 2020; Hayrapetyan et al., 2023; Minjares-Fuentes et al., 2014), Citrullus Lanatus (Watermelon) (Prakash Maran, Sivakumar, Thirugnanasambandham & Sridhar, 2014) and sisal waste (Santos, Espeleta, Branco & de Assis, 2013).

Pectin isolation from plant cell walls includes pre-treatment steps of raw material such as washing, blanching, and drying (May, 1990). Acidic extraction is the traditional and widely used industrial method used to obtain pectins. This extraction process is typically conducted in stirred batch reactors, where the raw material is subjected to acid treatment under high temperatures ranging from 80 to 100 °C and lower pH values of 1–3. The extraction time and conditions depend on the type of the raw material and range is between 30 and 180 min. Subsequent steps include alcohol precipitation, separation through drying and post-drying operations such as milling and sieving to achieve the desired powder granulometry. In laboratory-scale extractions, the plant extract containing pectin is separated from the raw material through filtration or centrifugation after alcohol precipitation. These last decades, the

development of alternative and green extraction techniques gained popularity (enzymatic, microwave and ultrasound-assisted extractions, subcritical water extraction (SWE), and supercritical fluid extraction (SFE) pushing researchers to explore new sources of pectin such as cranberry, onion, garlic, banana, mango, pumpkin, papaya, and grapefruit (Hayrapetyan et al., 2023; Liew, Teoh, Tan, Yusoff & Ngoh, 2018; Swamy & Muthukumarappan, 2017; Yoo et al., 2012). However, pectins extracted from these unconventional plant-based sources have some limitations such as being lower than the legal minimum amount of galacturonic acid (GalA) content (65% GalA) when the requirement thus cannot be designed as “pectin” for food and pharmaceutical applications (Willats et al., 2006). Moreover, scaling up these methods for industrial applications remains a significant challenge. To obtain low methoxyl pectin (LMP), a chemical transformation is required where the ester groups are hydrolysed through a process called demethylation. This can be achieved using acid, alkaline, or enzymatic treatments with methylesterase. Another method involves hydrolysis using ammonia, which converts ester groups into amide groups, resulting in amidated pectins (May, 1990). These transformations necessitate the use of harsh chemicals and expensive enzymes which contribute to increased production costs (Yapo & Koffi, 2014). Commercial pectins typically contain limited amounts of sodium and calcium. For technological purposes, they may also include sugar or dextrose and/or buffer salts for standardization (Endreb & Christensen, 2020; Thakur, Singh & Handa, 1997; Voragen et al., 1995). In addition to the standardization components mentioned earlier, commercial pectin products consist primarily of blends of multiple pure pectins that have similar chemical and macromolecular characteristics. This distinguishes them from pure pectins, which are not standardized. Therefore, it is crucial to consider these aspects and the presence of additional components when studying pectins.

## Techno-functional properties of pectins

### Pectin as a stabilizing and viscosifying agent

Stabilizing agents, also known as stabilizers, are biomacromolecules that can prevent sedimentation or limit the separation of dispersed or heterogeneous media (Guo, Wei, Cai, Hou & Zhang, 2021; Rubinstein & Colby, 2003; Wusigale, Liang & Luo, 2020). Various approaches can be employed to achieve stabilizing properties such as (i) increasing viscosity, which may be undesirable in certain applications where high viscosity affects the texturizing quality of the product, (ii) creating an efficient network structure that can maintain suspended particles without being perceptible in the mouth, and (iii) masking potentially interactive components in dispersed systems. Pectins are known to exhibit these stabilizing mechanisms, particularly in dairy products and
dairy analogues (Endreb & Christensen, 2020; Guo, Bayram et al., 2022; Wusigale et al., 2020). Moreover, the thickening / viscosifying property of the pectin is one of its key features that justifies its widespread use in the food industry. This property contributes to the desirable texture to food products such as fruit beverages, soft drinks, sports drinks, and sauces. Pectin has also been found to be beneficial for individuals with dysphagia and reflux problems. The concentration and the type of pectins used depend on the specific characteristics and texture desired in the final product. For instance, low-methoxy pectin (LMP) impacted positively the cloud stability and ascorbic acid retention in guava juice. When combined with gum Arabic, it increased overall acceptability with minimal impact on viscosity (Mousa, 2020). In low-calorie beverages where sugar is partially or wholly replaced with sweeteners, an undesirable change in mouthfeel can occur. Pectin is one of the agents used to restore the desired mouthfeel, as observed in beverages containing steviol glycosides according to the protected method of PepsiCo, Inc. (Brijwani & Mutilangi, 2021). Recent clinical trials conducted on infants younger than 5 months demonstrated that formula enriched with pectin as a thickener agent reduced regurgitation and was proven to be safe (Dupont & Vandenplas, 2020).

To address sensorial defects in whey protein beverages, it is ideal to formulate them within a pH range of 4–6. However, this range encompasses the isoelectric point (pI) of whey proteins, where protein precipitation, microphase separation, or gelation may occur after heating (Ako, Nicolai, Durand & Brotons, 2009). The behavior of whey proteins in this pH range is influenced by the type of pectin used, whether it is HMP or LMP. This depends strongly on the type of pectin (HM or LM pectin). HM pectin can act as a protein dispersion stabilizer at lower pH levels, whereas LM pectin behaves quite differently. LMP can be utilized to gel neutral milk desserts or serve as a texturizer in more acid products like stirred yoghurt, where it interacts with calcium and milk proteins (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). In acid dairy drinks (ADD), HM pectin has proven effective as a protective colloid for casein or similar protein particles at a pH of around approximately 4, as commonly seen in yoghurt (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). However, in high-protein content beverages, treatment at acidic pH can lead to protein aggregation and precipitation, resulting in the formation of larger clusters which later leads to a sandy mouthfeel (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). Therefore, the addition of HMP prior to fermentation of these ADD can bind to protein through their negatively charged carboxylic groups, protecting them from aggregation during heat treatment.

High methoxyl pectin plays a crucial role in creating a weak

molecular network in acidic dairy drinks (ADD), contributing to their stability. The presence of unabsorbed pectin chains may contribute to the stability of ADD by increasing the viscosity of the continuous phase, slowing down the sedimentation rate of protein aggregates (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). The stabilizing effects of HM pectin in ADD involve electrostatic repulsion, steric hindrance, viscosity enhancement, and weak network formation (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). Complexation can occur through electrostatic interactions between anionic polysaccharides (pectins) and positively charged surface patches (such as $-NH_3$ groups) on the proteins (Cooper, Dubin, Kayitmazer & Turksen, 2005; Tolstoguzov, 2003). This “charge patch” mechanism can be influenced by the charge regulation and ion-dipole interactions near the protein’s isoelectric point. Depending on the electrostatic conditions, the complexes can remain as small soluble complexes (SCs) or undergo associative or segregative phase separations (Fig. 3). The required dosage of pectin depends on the protein level and the size and organization of protein aggregates in the drink. Smaller aggregate sizes generally result in more stable drinks, but they may require increased pectin dosage due to a larger total surface area. The size of protein particles is typically controlled by optimizing fermentation or acidification conditions. However, the efficiency of the stabilizing effect of HM pectin in ADD strongly depends on its degree of esterification (DE) and calcium sensitivity. Pectin with DE > 70% has been shown to be effective in stabilizing ADD with a broad range of milk protein contents (0.5–3.0 g/L) when used at a concentration of > 0.25 g/L (Laurent & Boulenguer, 2003). While other polymers like carboxymethyl cellulose (CMC), soluble soybean polysaccharides (SSP), gellan gum, and propylene glycol alginate can also stabilize ADD, HM pectins are preferred due to the improved mouthfeel they impart. In addition to the use of HM pectin in ADD stabilization, LM pectin can be used in relatively low concentrations to increase viscosity, creaminess, and stability in various types of yoghurt (set and stirred) (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). In yoghurt and okra, pectin positively impacted consumer acceptability, enhancing its water holding capacity and reducing whey exudation (Tobil, Deh, Agbenorhevi, Sampson & Kpodo, 2020). The addition of orange peel pectin increased the viscosity, adhesiveness, and cohesiveness of the final product (Arioui, Djamel & Abderrahim, 2016). Complexes of whey protein-HMP have also been utilized as fat replacers in vanilla sauces, achieving apparent viscosities to fat-rich products (Protte, Weiss, Hinrichs & Knaapila, 2019).

In the dilute regime, where the pectin concentration is below the overlap concentration (c*), pectin chains are too far to interact with

<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Mechanism of the stabilization of milk proteins by addition of high methoxyl pectins (HMP). At low pH, the amount of COOH is predominant. HMP achieves this stabilization by (i) forming weak interactions with the proteins and (ii) enhancing the viscosity of the continuous phase.</figcaption></figure>
each other. In this regime (c < c*), the viscosity of the solution increases slightly with the pectin concentration. From a fundamental point of view, studying the pectin at low concentrations allows obtaining information on the intrinsic viscosity [η] as well as the chain conformations which are strongly affected by the nature and the concentration of the solvent (Alba, Bingham, Gunning, Wilde & Kontogiorgos, 2018). As the concentration of pectin increases (c > c*), the distance between pectin chains decreases facilitating intermolecular interactions such as hydrogen bonding and/or hydrophobic and/or electrostatic interactions. At low concentrations, pectin solutions exhibit Newtonian behaviour meaning that the viscosity remains constant regardless of the shear rate. However, above a certain concentration (c*), pectin solutions exhibit shear thinning behaviour, where the viscosity decreases with increasing shear rate. The value of c* depends on the molecular weight of the pectin used (Chan, Choo, Young & Loh, 2017). It is expected to obtain high viscosity values with a higher average molar mass. However, other intrinsic and extrinsic parameters can also affect the viscosity. The viscosity of pectin increases with the degree of esterification (DE) and the content of galacturonic acid (GalA). It is also affected by factors such as pH, and salt (nature and concentration) (Reichembach & Lucia de Oliveira Petkowicz, 2021). Guimaraes et al. observed that pectin solutions at more acidic pHs exhibit higher viscosity compared to the other pH values (ranging from 3 to 6) due to increased hydrophobic interactions of the ester methyl groups (COOCH₃) (Guimaraes, Coelho Júnior & Garcia Rojas, 2009).

There are a strong interest in the consumption of beverages, particularly pectin-based drinks, enriched with whey proteins, due to implications for health benefits such as increased satiety and metabolic regulation. However, the low thermal stability restricts the formulation conditions for these beverages. Research has shown that at a specific pH range near the protein isoelectric points of the proteins, whey proteins and polysaccharides self-assemble into soluble complexes (SCs) that possess unique functionality. Currently, the market tendency is to design novel pectin-based drinks that are enriched with higher amounts of proteins and minerals, targeting the elderly, athletes, and children. However, such drinks are prone to precipitation under specific conditions such as temperature, time, and pH. To overcome these issues, the addition of high molecular weight pectin (HMP) has been proven to be an effective technical solution. When the appropriate dosage is applied, HMP enhances the stability of these complex beverages. Furthermore, using HMP instead of other hydrocolloids offers additional advantages, including the absence of gelation and improved desirable mouthfeel.

## Pectin as a gelling agent

The gelation of pectin can be achieved differently according to the nature of the pectin and more specifically the degree of methyl esterification (DE). The HM pectins (HMP) undergo gelation only in the presence of sugars or other co-solutes above 60% (typically 55 – 75%), and at a sufficiently low pH (e.g., pH 2.5 – 3.5) where the acid groups in the polymer are not completely ionized (Endreb & Christensen, 2020). However, low methoxy pectins (LMP) and amidated low methoxy pectins (ALMP) are known to form gels in the presence of divalent cations such as calcium ions over a wide range of pH values (pH 2.6 – 7) with or without added co-solutes (Axelos & Thibault, 1991; Endreb & Christensen, 2020). It has also been demonstrated that both LMP and ALMP can undergo gelation at very low pH (< 3) (Capel, Nicolai, Durand, Boulenguer & Langendorff, 2006). LM pectin has been shown to gel in the absence of Ca²⁺ by lowering the pH below ~3.3, which is attributed to the gradual reduction in the charge density of the pectin as the pH decreases from pH 4.5 (Gilsenan, Richardson & Morris, 2000). Amidation of pectin has been found to enhance acid-induced gelation without significantly modifying the sensitivity to Ca²⁺, resulting in the formation of weak gels even in the absence of Ca²⁺ for fully charged pectin (Lootens et al., 2003). For calcium-dependent gelation, it has been established that the affinity of pectins for calcium ions increases as the DE of

pectins and the ionic strength of the system decrease (Garnier, Axelos & Thibault, 1993). Polymer concentration also increases the affinity of pectin chains for calcium ions. According to Garnier et al. (Garnier et al., 1993), pectin-calcium interactions are anti-cooperative in water but become cooperative in the presence of 0.1 M NaCl. The reactivity of LMP and ALMP to calcium is also influenced by the proportion and arrangement of carboxyl groups of the pectin molecule. Reactivity increases with decreasing DE and is higher but less controllable for gelling purposes when the arrangement of acid groups is less random, with blocks of de-esterified galacturonate units (Cao, Lu, Mata, Nishinari & Fang, 2020; Endreb & Christensen, 2020; Li, Gao et al., 2021). Pectin amidation has emerged as an interesting option to optimize the use of LMP in applications where high calcium levels can lead to pre-gelation issues (Cao, Lu et al., 2020; Endreb & Christensen, 2020; Li, Gao et al., 2021). Indeed, ALMP can stabilize junction zones in the resulting gel network structures through additional hydrogen bond formation with the amide groups. Another advantageous quality of amidated LM pectins is their ability to form gels under low-sugar conditions, unlike non-amidated LM pectin (Endreb & Christensen, 2020). While the gelation mechanism of LMP and ALMP following the egg-box model, as observed in alginate, has been proposed, this model is still a matter of debate (Cao, Lu et al., 2020). The network structure of the ALMP is build-up through various interactions, such as calcium bridges formed by the complexation of two consecutive carboxyl groups of galacturonic acid (GalA) units of the pectins, hydrophobic interactions involving methyl groups, hydrogen bonds between undissociated carboxyl groups, and those formed by the amide groups (Cao, Yang et al., 2020; Capel et al., 2006; Endreb & Christensen, 2020; Fraeye, Colle et al., 2010; Lootens et al., 2003). The gelation mechanism of LMP and ALMP is affected by several parameters, such as pectin concentration, DE and/or DA values, molecular weight, pH level, water activity, sequestrants, ionic strength, sucrose concentration, and rate of cooling (Table 1). When sucrose content increased, the gel strength improved because of the enhanced number of hydroxyl groups in the junction zones and the promotion of hydrogen bonding to immobilize free water (Cao, Lu et al., 2020; Han et al., 2017; Norziah, Foo & Karim, 2006). LMP has a great potential for low-calorie food and encapsulation of thermosensitive molecules (proteins, enzymes, probiotics, ...) (Heumann et al., 2020; Maire du Poset, Börjesson et al., 2020).

During the gelation of HMP, high temperature causes the dissociation of pectin chains (Fig. 4), and the addition of H⁺ prevents the

<caption>**Table 1**</caption>

Classification of pectins according to their types, degree of esterification and gelation conditions (Endreb & Christensen, 2020; Gallery, Agoda-Tandjawa, Bekaert & Gitto, 2024; Thakur et al., 1997; Voragen et al., 1995).

<table><thead><tr><th>Type of pectins</th><th>DE (%)</th><th>Gelation conditions</th><th>Gelation rate</th><th>Classification</th></tr></thead><tbody><tr><td rowspan="6">HM pectin</td><td>75 - 77</td><td rowspan="6">Brix &gt; 55°, pH 2.5 - 3.5</td><td>Extra rapid</td><td>Extra rapid set pectin</td></tr><tr><td>68 - 74</td><td>Rapid</td><td>Rapid set pectin</td></tr><tr><td>64 - 67</td><td>Fairly rapid</td><td>Medium rapid set pectin</td></tr><tr><td>58 - 65</td><td>Slow</td><td>Slow set pectin</td></tr><tr><td>57 - 60</td><td>Extra slow</td><td>Extra slow set pectin</td></tr><tr><td>60</td><td>Extra slow</td><td>Extra slow set pectin</td></tr><tr><td rowspan="3">LM pectin</td><td>30</td><td rowspan="3">Calcium ion (mg/ g pectin) and pH 2.6 - 7</td><td>Rapid</td><td>High calcium reactivity pectin</td></tr><tr><td>40</td><td>Fairly rapid</td><td>Medium calcium reactivity pectin</td></tr><tr><td>50</td><td>Low</td><td>Low calcium reactivity pectin</td></tr><tr><td rowspan="2">ALM pectin</td><td>30</td><td rowspan="2"></td><td>Rapid</td><td>High calcium reactivity pectin</td></tr><tr><td>35</td><td>Low</td><td>Low calcium reactivity pectin</td></tr></tbody></table>
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Mechanism of gelation of high methoxy pectin (HMP). The heat of HMP allows the dissociation of pectin chains (1). The decrease of pH transforms carboxylate groups into carboxylic groups promoting the formation of hydrogen bonds between the chains (2). The introduction of sucrose at a high concentration reduces the water activity and promotes the association of pectin chains (3). The 3D network will be stabilized after the cooling step.</figcaption></figure>

dissociation of free carboxyl groups of GalA (pH<pKa ~3.5), thus reducing electrostatic repulsion between molecular chains (Thibault & Ralet, 2003). Meanwhile, the high amount of sugar reduces the hydrated radius of pectin, promoting inter-chain interactions instead of chain-solvent interactions (knowing as the sugaring-out effect) (Fu, Li, Sun & Xie, 2021). Indeed, sugar “restructures” water molecules, leading to an increased local concentration of polysaccharides (Lopez-Sanchez et al., 2022). Moreover, the presence of large number of methyl ester groups promotes inter-chain interactions by creating hydrophobic bonds. The structure of the gel is either stabilized by (i) hydrogen bonds between undissociated carboxyl and alcohol groups of the pectin, or (ii) hydrophobic interactions between methoxy groups and water. The three-dimensional network (gel) forms during the cooling process. The industrial example of such gelation is the production of jams.

Compared to HM pectin, LM pectin can form a three-dimensional (3D) network at room temperature in the presence of various divalent and multivalent cations (except Mg²⁺). This gelation is known as ionotropic gelation and can occur either internally or externally (Secchi et al., 2014). The internal gelation consists of the gradual release of divalent cations from an insoluble cation source (such as CaCO₃ or CaSO₄) in the pectin solution (Ventura, Jammal & Bianco-Peled, 2013), while the external gelation consists of the diffusion of divalent cations from an external reservoir to the pectin solution (Caccavo, Ström, Larsson & Lamberti, 2016; Martinsen, Skjåk-Bræk & Smidsrød, 1989; Thu et al., 2000). In these two cases, the gelation occurs between dissociated GalA units present in the pectin and divalent cations. Several comprehensive reviews (Cao, Lu et al., 2020; Celus, Kyomugasho, Van Loey, Grauwet & Hendrickx, 2018; Fraeye, Duvetter, Doungla, Van Loey & Hendrickx, 2010; Williams, 2020) have focused on the gelation mechanism and the gel structure obtained by the ionotropic gelation.

For a long time, the association between GalA units and divalent cations was described by the widely accepted “Eggbox model” (Grant, Morris, Rees, Smith & Tho, 1973). This model explains ionotropic gelation as the cooperative association of chains mediated by divalent cations, forming arrays of ionic bridges between the guluronate units (GulA) in alginates or the galacturonate units (GalA) in pectins, known as junction zones. Although the “egg-box model” is considered essentially correct because it can describe the main features of gelation, the exact coordination geometry of divalent cations in junction zones

remains unclear, due to the difficulty of current experimental techniques to probe cation-ligand interactions in disordered systems (Maire du Poset, Zitolo, Cousin, Assifaoui & Lerbret, 2020). From the molecular dynamic simulations, Braccini et al. (Braccini & Perez, 2001) have proposed a “shifted egg-box” model to describe the structure of calcium pectinate. Fraeye et al. (Fraeye, Duvetter et al., 2010) analysed numerous publications on the effect of chain length on pectin gel formation and suggested a critical chain length range from 6 to 14 (Kohn, 1975; Powell, Morris, Gidley & Rees, 1982). Recent molecular dynamic (MD) simulations of GalA chains in explicit water showed that the “egg-box” model is more adapted for zinc cations than for calcium ones (Assifaoui et al., 2015; Bodart et al., 2022; Plazinski, 2011). Indeed, it was found that Zn²⁺ interacts with both carboxylate and hydroxyl groups of the galacturonate units, in a similar way to that described in the “egg-box” model, whereas calcium cations only interact with carboxylate groups (Fig. 5). Recent studies have shown that the mode of the association of divalent cations to carboxylate groups of GalA follows the monodentate model in the case of Zn²⁺ and Fe²⁺ (Eggbox model) and the bidentate model in the case of Ca²⁺ and Ba²⁺ (Assifaoui et al., 2015; Huynh, Assifaoui & Chambin, 2017; Maire du Poset, Zitolo et al., 2020). In other words, the association between X²⁺ and COO⁻ of GalA requires a release of one water molecule (monodentate) or two water molecules (bidentate). The mode of association is intimately related to the strength of the interaction between the cation and its hydration shell. The affinity of divalent cations for water molecules is found to increase in the following order: Ba²⁺ < Ca²⁺ < Zn²⁺ < Fe²⁺ << Mg²⁺ (Assifaoui et al., 2015; Huynh et al., 2017; Kohn, 1975; Maire du Poset, Zitolo et al., 2020). Therefore, Mg²⁺-polyGalA remains as a solution and only polycondensation seems to occur (Donati, Asaro & Paoletti, 2009). Mg²⁺ interacts so strongly with water that it remains weakly bound to polyGalA (polycondensation) by sharing water molecules from its first coordination shell with the carboxylate groups of polyGalA (Huynh et al., 2017) (Fig. 6).

The gelation mechanism of divalent cation to pectin, below the overlap concentration (C < C*), has been a topic of debate among several authors (Donati, Benegas & Paoletti, 2006; Fang et al., 2007; Li, Fang, Vreeker, Appelqvist & Mendes, 2007; Ventura et al., 2013) and has been summarized in recent reviews (Cao, Lu et al., 2020; Celus et al., 2018; Williams, 2020). In 2007, Fang et, al. (Fang et al., 2007) proposed
<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Mode of association of divalent cations (X²⁺) to Galacturonic units (GalA). For the Eggbox model, X²⁺ is monodentately coordinated to two carboxylates and two hydroxyl oxygens from a pair of polyGalA chains as well as to two water oxygens. According to MD simulations, calcium and barium ions interact in bidentate mode; while zinc and iron(II) ions interact in monodentate mode following the eggbox model.</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Gelation mechanism of GalA units in the presence of various divalent cations. In the absence of divalent cations, polyGalA chains are distributed randomly in the solution (c < c*). The addition of Mg²⁺ doesn't allow to form a gel. Mg²⁺ interacts so strongly with water that it remains weakly bound to polyGalA (polycondensation) by sharing water molecules from its first coordination shell with COO⁻ of GalA units (SSIP). For the other cations and at low molar ratio R ([X²⁺]/[GalA]), the monocomplexation and the formation of point-like cross-links occur upon increasing R. Above a threshold molar ratio R*, the network of polyGalA chains reorganizes and dimers as well as supplementary point-like crosslinks are formed (Huynh et al., 2017). R* depends on the nature of considered divalent cation owing to differences in the number and the stability (or lifetime) of the point-like crosslinks that they form with polyGalA chains, which are related to their affinity towards water. R* is lower for Ca²⁺ than for Ba²⁺ and Zn²⁺ and Fe²⁺ because Ca²⁺.</figcaption></figure>

a gelation mechanism between Ca²⁺ and pectin that involves successive steps, including (i) monocomplexation at a low molar ratio, R= Ca²⁺/GalA, followed by (ii) dimerization (0.25< R < 0.55) and, then, (iii) by the lateral association of dimers (multimerization) (R > 0.55). They have suggested that in the case of LMP, the lateral associations could occur due to structural features of the pectin: the random distribution of ester and/or amide groups along the pectin chain introduces much more defects in the formation of dimers and even hinders the subsequent lateral association of dimers (Cao, Lu et al., 2020; Fang et al., 2008). In this initial gelation mechanism, the monocomplexation as an independent step which occurs at a low molar ratio (R < 0.25) is discussed here. It should be noted that the monocomplexation step has a short lifetime. MD simulations have shown that full monocomplexation of Ca²⁺ and Zn²⁺ cations are completed within 10 and 42 ns, respectively. Therefore, the monocomplexation is immediately followed by the formation of point-like crosslinks (GalA-X²⁺-GalA) as demonstrated by several researchers (Borgogna, Skjåk-Bræk, Paoletti & Donati, 2013; Huynh et al., 2017; Ventura et al., 2013). The simultaneous formation of monocomplexes and point-like crosslinks appears to be the first step in

gelation and is found to be an entropically driven phenomenon due to the dehydration of divalent cation (loss of water molecules from the cation hydration shell) (Bertz et al., 2013; Celus et al., 2018; Huynh et al., 2017). The second step is the formation of an ordered structure (dimers or multimers) and it is found to be enthalpically driven, as shown by isothermal titration calorimetry (ITC). The second step appears when the amount of the divalent cation increases above a threshold molar ratio (R*). It has been found that R* depends on the nature of divalent cations and is lower for calcium ions (R* < 0.1) than for zinc and barium ions (R* > 0.3) (Celus et al., 2018; Huynh et al., 2017). These differences have consequences on the number and the stability (lifetime) of the cross-links formed between polyGalA chains, which are a key step for the mechanism of association. The cross-links formed must probably be of adequate stability and numerous enough to allow the dimerization step to occur (Huynh et al., 2017) (Fig. 6).

Structure of the cation-pectin hydrogels (C > C*): Understanding the mode of association between X²⁺ and polyGalA is of great importance since it may strongly affect the structure and mechanical properties of the macroscopic gel as shown by several authors (Agulhon, Markova,
Robitzer, Quignard & Mineva, 2012, 2014; Huynh, Chambin, du Poset & Assifaoui, 2018; Maire du Poset et al., 2019; Mørch, Donati & Strand, 2006). It is well-known that external gelation allows the formation of an anisotropic gel where a gradient of the polymer concentration and macroscopic pores are observed (Assifaoui, Loupiac, Chambin & Cayot, 2010; Caccavo et al., 2016; Huynh et al., 2018; Martinsen et al., 1989; Potter, Balcom, Carpenter & Hall, 1994; Thu et al., 2000). The gel formation between pectin and divalent cations exhibits a gelation front that subsequently progresses across the liquid polymer to leave gelled calcium-polysaccharide behind (Hills et al., 2000) (Fig. 7). The diffusion of X²⁺ from an external reservoir through a dialysis membrane to the polyGalA solution (C > C*), allowed the formation of many point-like crosslinks which are located near to the dialysis membrane. When the molar ratio (R=[X²⁺]/[GalA]) is higher than R*, these point-like crosslinks become dimers and multimers. This induced a contraction of the polymer chains and thus the formation of the gel front (See Fig. 6 from Ref. (Huynh et al., 2018)).

Anisotropic cation-pectin hydrogel exhibits a gradient in mesh size based on the diffusion direction of the cation. The distribution of porosity can result in either homogeneous or heterogeneous structures depending on the type of divalent cations (Fig. 7) (Maire du Poset et al., 2019). In the denser region of the gel, which corresponds to the bead's periphery (Fig. 7), it has been demonstrated that the mesh size is solely dependent on the pectin chains' persistence length (Lp) and the initial concentration of pectin (Maire du Poset, Börjesson et al., 2020; Maire du Poset et al., 2019). However, in the less dense region, which corresponds to the core of the bead (Fig. 7), the distribution of mesh size is homogeneous for calcium-pectin hydrogels due to the bidentate association between the cation and GalA. On the other hand, for zinc-pectin and iron (II)-pectin hydrogels with monodentate associations between the cation and GalA, the distribution of mesh size is heterogeneous.

Understanding and controlling the gelation mechanism and kinetics of pectin is crucial for formulators and food ingredient suppliers. It is essential for sustainable innovation and ensuring the quality of the final product. By identifying the specific application area, such as neutral, acidic, hot, or cold gels, pectin can serve as a desirable alternative to certain undesirable ingredients. However, the challenges associated with different pectin types must be considered from multiple perspectives. Low methoxyl pectin (LMP) can be suitable for applications where traditional gelation conditions are not appropriate. In such cases, formulators can explore alternative sources of calcium, such as milk protein or insoluble salts like calcium citrate and calcium phosphate. On the other hand, for high methoxyl pectin (HMP) gelation, additional components must be incorporated to compensate for the reduced sugar content and maintain the desired water activity. Currently, certain food ingredients are facing controversy due to factors such as price, health

concerns, and wellness considerations. Consequently, there is a market trend towards replacing these undesirable ingredients partially or completely with label-friendly alternatives. Pectin emerges as a promising candidate for numerous applications as it can fulfil customer requirements by preserving texture and sensory qualities in the final product.

## Pectin as an emulsifier

In addition to its traditional uses as gelling, stabilizing, and viscosifying agent, pectin is increasingly being recognized as an effective food emulsifier (Alba & Kontogiorgos, 2017; Mendez et al., 2021; Neckebroeck et al., 2021, 2019, 2020; Ngouémazong, Christiaens, Shpigelman, Van Loey & Hendrickx, 2015). This multifunctional natural food additive is gaining acceptance due to the growing demand for natural, sustainable, and eco-friendly ingredients with interfacial properties. Pectin can serve as a natural alternative to commonly used synthetic surfactants, such as tweens and spans. Apart from pectin, other polysaccharides such as gum Arabic (Acacia Senegal), modified cellulose derivatives, modified starches, galactomannans (e.g., guar, fenugreek gums), and soy soluble polysaccharides were also used as emulsifiers (Ngouémazong et al., 2015). However, pectin holds an advantage among these polysaccharides due to its versatile nature. It can act as a stabilizer in water/oil (w/o) interfaces, provide nutritional value as a dietary fiber, and enjoy customer acceptability. Pectin is generally regarded as the safest and most acceptable food additive, as recognized by regulatory bodies such as EFSA (European legislation) and GRAS (United States legislation) (Endreb & Christensen, 2020). In this context, pectin is increasingly used as a mono-emulsifier in many applications such as emulsified mineral and vegetable oils, low-fat mayonnaise, reduced-fat dairy products, emulsified meat products and to name but a few (Endreb & Christensen, 2020). The potential of pectin as an emulsifying and emulsion stabilizing (EES) agent was extensively explored in the last three decades, as recently reviewed by (Alba & Kontogiorgos, 2017; Ngouémazong et al., 2015). Most studies focused on EES potential are dedicated to sugar beet and citrus pectin. However, more recent studies have focused on other pectins extracted from various and different botanical sources such as okra, watermelon rind, apple pomaces, chopped onions, tomatoes and carrot (Mendez et al., 2021; Neckebroeck et al., 2021, 2019, 2020).

The mechanisms behind the emulsifying and emulsion stabilizing (EES) properties of pectin have been extensively studied and reviewed (Alba & Kontogiorgos, 2017; Ngouémazong et al., 2015). These functional properties are governed by both the intrinsic characteristics of pectin (proteinaceous moiety, ferulic and acetyl contents, galacturonic acid content, molecular weight, neutral sugar side chains, degree, and

<figure><img src="image_10.png" /><figcaption>**Fig. 7.** External gelation induces a decrease of the Young modulus and the pectin concentration from the periphery to the core of the cation-pectinate bead. In the bead periphery, the mesh size is independent of the nature of divalent cation and seems to be more related to the persistence length of the pectin. In the bead core, the pectin network structure is cation dependent and seems to be more homogeneous for cations which bind the carboxylate groups of GalA through bidentate mode and more heterogeneous for cations binding the carboxylate groups of GalA through monodentate mode.</figcaption></figure>
pattern of methyl-esterification) and extrinsic factors such as pectin concentration, ionic strength, and pH. Recently, (Alba & Kontogiorgos, 2017) compiled information from the literature to identify the desired qualities of an "ideal" pectin for effective interfacial arrangement, efficient emulsification, and long-term stabilization. They proposed that pectin with a protein content in the range of 3%, a degree of acetylation greater than 10%, a molecular weight between 100 and 200 kDa, and enriched in RG-I segments and ferulic acid could be suitable as a good emulsifier. They suggested achieving these characteristics through aqueous extraction at low pH values (pH 2.5 - 3.5) using a strong monotropic acid (e.g., HCl), followed by alcohol precipitation. However, the use of such extraction conditions with a strong monotropic acid raises questions regarding compatibility with current industrial extraction approaches, as discussed previously. Additionally, it's important to note that the botanical source of the raw pectin material plays a significant role in terms of quantity and quality and should be considered during pectin processing for emulsifying purposes.

The interfacial activity of pectin is related to the presence of proteinaceous moieties acting as hydrophobic anchors which facilitate the adsorption of pectin chains at the interface reducing the interfacial tension. However, the accessibility and chemical nature of the protein, including the composition of amino acids and conformation, are the primary determinants of this activity (Alba & Kontogiorgos, 2017; Ngouémazong et al., 2015). Indeed, the protein anchors in the pectin chains at the interface are supported by acetyl and methyl groups and, when available, ferulic acid. Once adsorbed, pectin could also contribute to long-term emulsion stability using steric and/or electrostatic effects. The adsorbed pectin forms thick hydrated layers at the oil-water interface, creating steric hindrance that increases emulsion stability by preventing droplet coalescence (Alba & Kontogiorgos, 2017; Ngouémazong et al., 2015). These steric effects are mainly attributed to the side chains of the rhamnogalacturonan-I (RG-I) structural element in the pectin polymer. In addition to the steric effects, oil droplets stabilized by pectin can also experience electrostatic interactions. The negatively charged GalA residues give the pectin its polyanionic character. When pectin adsorbs at the oil-water interface, it creates a negatively charged layer around the oil droplets leading to electrostatic repulsive forces between the emulsified oil droplets, thereby increasing emulsion stability against aggregation (Fig. 8). Generally, the protein moiety, ferulic acid, methyl, and acetyl groups, play a significant role in pectin's emulsifying activities, while the emulsion-stabilizing properties of the polymer are controlled by the homogalacturonan (HG) domain, the neutral sugar

side chains of the RGI structural element and the other related parameters. However, the neutral sugar side chains may hinder the accessibility of hydrophobic species in pectin to oil/water interface, limiting its emulsifying ability. Furthermore, the contribution of HG domain to emulsion stabilization may depend on the ratio of HG to RGI in the polymer (Alba & Kontogiorgos, 2017).

Although considerable research has been conducted to understand the structural characteristics of pectins, raw materials variability, extraction procedures and the emulsion composition, there is still much to be done to ensure the efficient control over pectin's fine structure and its functionalities as an EES agent. The structural complexity of pectin polymers makes it extremely challenging. However, utilizing pectin as an effective EES agent in certain food applications can offer an alternative to synthetic surfactants while satisfying sensory and texturizing requirements, meeting consumer expectations. Apart from this research challenge, positioning some types of pectins as EES agents on the market could be seen as economically non-viable from the supplier and food processing industry points of view. The latter could decrease the global market demand of pectins which were used for their traditional properties such as gelling, stabilizing, viscosifying, and gelifying properties. Additionally, a yearlong availability of pectin raw material to the supplier chains for above mentioned applications remains questionable. The demand for healthier, natural, and sustainable multifunctional emulsifiers is on the rise, driven by consumer preferences for clean-label products. The continuous research and development efforts in the production of effective polysaccharide emulsifiers offer promising opportunities for market players in the future. Pectins, among the available polysaccharide emulsifiers, have great potential due to their multifunctional properties and customer preference, surpassing other EES agents such as chemically modified starches and cellulose derivatives. Despite the significant potential of pectins, their positioning as an effective natural and sustainable emulsifier in the market is still evolving. However, recent research on the EES properties of pectins could lead to the introduction of new botanical sources of pectins and the utilization of sugar beet pectins as a natural emulsifier (Endreb & Christensen, 2020), despite the aforementioned challenges. Food ingredient suppliers and food processing industries should promote pectins that exhibit excellent interfacial properties with minimal gelling characteristics, such as sugar beet pectin, onion pectin, okra pectin, grape pectin, and others.

<figure><img src="image_11.png" /><figcaption>**Fig. 8.** The presence of protein moieties and ferulic units covalently bound to the pectin backbone can be adsorbed at the oil-water interface. The high Mw of the pectins allows to stabilize emulsion by increasing the viscosity of the continuous phase.</figcaption></figure>
## Other techno-functional properties of pectins

In this section, we will focus on other pectin functionalities which are mainly driven by the main three functions of pectins (viscosifying, gel-ling, and emulsifying). This includes the ability of pectins to (a) encapsulate active molecules, (b) form films and coating, and (c) adsorb substances which can be either desirable (extraction of adding value minerals) or undesirable (binding heavy metals for water treatment).

### Encapsulating agents for active molecules

Thanks to their biocompatibility, biodegradability, and non-toxicity, pectins have long been used as encapsulating matrices for bioactive molecules to target the release of an active component into the colon. Indeed, the presence of pectinolytic enzymes in the human colon will degrade the pectin matrix and release the drug into the colon. This versatile property makes pectin a suitable candidate for colon-targeted oral drug release systems, which can be used for the systemic treatment of ulcers, Crohn's disease, colon carcinoma and other pathologies (Das & Arora, 2021; Noreen et al., 2017; Rehman et al., 2019; Wong, Colombo & Sonvico, 2011). Pectin, either alone or in combination with other excipients, can be found in various dosage forms for pharmaceutical applications such as oral (tablets, patches, films, gastro-retentive dosage, floated systems), cutaneous, nasal delivery, ocular, vaginal, parenteral (see Table 20.1 in (Assifaoui & Chambin, 2020)).

The formulation of encapsulation matrices using low methoxy pectin (LMP) relies on its ability to gel at room temperature with the help of divalent cations (refer to section 3.2). This property is particularly advantageous for encapsulating thermosensitive molecules such as vitamins, antioxidants, enzymes, proteins, and probiotics (Assifaoui, Bouyer, Chambin & Cayot, 2013, 2011; Cargnin, Gasparin, dos Santos Rosa & Paulino, 2021; Dhalleine et al., 2011; Heumann et al., 2020; Huynh et al., 2017; Jantrawut, Assifaoui & Chambin, 2013). Divalent cations can be introduced during the preparation of the dosage forms or utilize the existing divalent cations present in body fluids to form in-situ hydrogels, such as in nasal sprays or ocular applications. Pectin solutions can rapidly gel upon eye contact due to the presence of electrolytes in tears (Giunchedi, Conte, Chetoni & Saettone, 1999). Recent studies have demonstrated that Fe(II)-pectin hydrogels made by Fe²⁺ as the cross-linking agent, protect iron against oxidation making them suitable for iron fortification (Huynh et al., 2018). Furthermore, calcium-pectinate beads have been used to form spherical microcolonies of the probiotic Lactobacillus paracasei as biofilm-like (Heumann et al., 2020). For hydrophobic active molecules (Vitamins), the strategy is to formulate an emulsion oil/water where the oil droplets carry the active molecules, and the continuous phase is composed of pectin (section 3.3). In this case, the dosage form is obtained by the gelation of the emulsion or by drying it with spray dryer (Noreen et al., 2017; Rehman et al., 2019; Ruffin, Schmit, Lafitte, Dollat & Chambin, 2014). Recent work has shown that calcium-pectinate beads allow the encapsulation of a fungicide (carbendazim) and delay its release, making them promising candidates for sustained and economical pesticide delivery systems (Bellemjid et al., 2021).

When the drug molecules are smaller than the mesh size of the hydrogel, they can diffuse more easily through the gel matrix, resulting in faster release. On the other hand, if the drug molecules are larger than the mesh size, their diffusion becomes restricted, leading to a slower release rate. Therefore, formulating pectin hydrogels with a specific mesh size is crucial for controlling the release of drugs. By optimizing the mesh size, researchers can achieve desired drug release kinetics, whether it's a sustained release over an extended period or a rapid release for immediate therapeutic effect. For pectin-based drug delivery systems, the efficacy and specificity to colon release must be justified by reliable in-vitro and in-vivo model and clinical trials (Assifaoui et al., 2011). The majority of pharmaceutically active molecules are hydrophobic, to encapsulate them, it is important to find out efficient methods which produce pectin derivatives that are more water-resistant and yet

enzymatically labile. Currently, the production of pectinate beads remains limited to laboratory scale and there is a need to enhance the feasibility of scaling up such versatile colon drug delivery systems. Moreover, controlling the drying process of such beads is crucial for maintaining the activity of the drug and its stability during storage.

### Coating and film-forming agents

Edible pectin films and coatings can be used to preserve the quality of fruits and vegetables by extending their shelf-life, preventing browning reactions, deterioration, microbial growth, and oxidation reactions (Huang et al., 2021; Nastasi, Kontogiorgos, Daygon & Fitzgerald, 2022).

The film-forming and coating properties of pectin are achieved through its ability to interact with similar or other biopolymer molecules via covalent, ionic, cation-mediated, non-ionic interactions, and self-assembly, resulting in the formation of a network structure (Lazaridou & Biliaderis, 2020). Film preparation methods such as casting, spraying, and extrusion are commonly employed (Huang et al., 2021). Casting involves dissolving the pectin with plasticizers (such as glycerol), followed by casting and drying. Spraying is a wet process that includes dissolving, spraying, and drying stages. During drying, the tensile strength, elastic modulus, and glass transition temperature (Tg) of the film increase. As water evaporates from the pectin solution, the plasticizing agents fill the gaps between polymer chains, preventing the formation of a rigid polymer matrix (Kalathaki, Alba, Muhamedsalih & Kontogiorgos, 2019). The extrusion process comprises feeding, kneading, and heating zones, with heating above Tg facilitating plasticization. This method is associated with the thermoplastic behavior of film components (Suhag, Kumar, Petkoska & Upadhyay, 2020). The properties of pectin films, including permeability, mechanical strength, and structure, are significantly influenced by pectin's molecular structure (such as branched structure, %Gala, DE, DA, and DB), size distribution, presence of plasticizers (type and quantity), crosslinkers, pectin concentration, and solvent nature (ionic strength, pH) (Lazaridou & Biliaderis, 2020).

Pectin-based films have excellent barrier properties against gas diffusion and permeability, specifically for gases like oxygen (O₂) and carbon dioxide (CO₂). However, their hydrophilic nature poses a significant limitation. This challenge can be addressed by incorporating hydrophobic plant extracts such as essential oils and insoluble fibers (CMC) into the pectin films (Panahirad et al., 2021). Additionally, the incorporation of antimicrobials, anti-browning agents, and antioxidants into pectin-based films or coatings, known as "smart" or "active" packaging systems, offers further advantages such as better control over the release of active molecules and efficient preservation (Lazaridou & Biliaderis, 2020). Panahirad et al. (2021) have compiled a list of natural antimicrobials, antioxidants, anti-browning substances, and probiotic microorganisms that can be incorporated into pectin films for the preservation of fruits and vegetables (refer to Tables 1-3 in (Panahirad et al., 2021)). Composite films, formed by combining pectin with various biodegradable materials such as whey protein, starch, polyvinyl alcohol, gellan gum, alginate, gelatin, cellulose, and chitosan (in bilayer or conglomerate forms), enhance the functionality of the films (Panahirad et al., 2021). Another strategy aimed at improving the quality and properties (mechanical, barrier, etc.) of pectin-based films involves the incorporation of nanoparticles (NPs) as reinforcing agents, such as nanocellulose and nanoclays. Certain nano-fillers like Ag NPs, Ag-Zeolite, and metal oxides provide antimicrobial or antioxidant activity, facilitate enzyme immobilization, and possess self-sterilizing properties (Cakmak & Sogut, 2020; Chavan et al., 2022).

From a fundamental perspective, it is essential to gain a deeper understanding of how the composition, structure, and processing of active pectin-based films influence their efficacy, quality, and preservation capabilities. Currently, the formulation of such active biopolymer-based films and coatings is primarily limited to laboratory-scale production. Future research endeavors could explore the feasibility of scaling up the production of these materials for industrial applications. Additionally,
the development of biobased nanocomposites necessitates optimization of the formulation process while adhering to regulatory guidelines that address concerns related to the migration of nanomaterials from packaging into food matrices and the reduction of production costs (Cakmak & Sogut, 2020).

## Adsorbing agent

The growth of industrialization and urbanization has resulted in the accumulation of bio waste in water resources. Consequently, untreated wastewater originating from industries such as printing, paper, textiles, batteries, pharmaceuticals, and food processing generates a significant amount of inorganic pollutants (such as heavy metal ions and nutrients) and organic pollutants (including dyes, pharmaceuticals, phenols, and oils). Among the heavy metal ions commonly found in wastewater are arsenic, copper, lead, mercury, nickel, cobalt, and chromium (Li et al., 2022; Wang et al., 2019).

In this context, pectin exhibits favorable adsorption capabilities for heavy metals. On a positive note, pectin can be utilized as a flotation depressant (reagent) to facilitate the efficient extraction of highly valuable minerals like manganese, molybdenum, and tungsten (Jiao, Dong, Qin, Liu & Hu, 2019; Wang et al., 2021).

Pectin possesses various functional groups, including hydroxyls, carboxyl, ester, and amide (in the case of ALMP), which can interact with water pollutants (Qi, Lin et al., 2019, 2019). For multivalent cations, the adsorption mechanism of pectin can be explained by the "egg-box" model (refer to Fig. 5), ionic exchange, complexation, and/or physical restraint. The adsorption capacity and selectivity of pectin for heavy metals are the subject of debate (refer to Table 2 in the reference by (Wang et al., 2019)). It appears that pectin exhibits a higher affinity for binding trivalent cations (such as $Cr^{3+}$ and $Fe^{3+}$) compared to divalent cations. This affinity is more pronounced for transition metals ($Cu^{2+}$, $Pb^{2+}$, $Zn^{2+}$, $Cd^{2+}$, $Fe^{2+}$) than for alkaline earth metals ($Ca^{2+}$, $Mg^{2+}$, etc.). This difference in affinity may be attributed to the

<table><caption>**Table 2**
Details of some food applications where pectins are used.</caption><thead><tr><th rowspan="2">Applications</th><th colspan="4">Media conditions</th><th rowspan="2">References</th></tr><tr><th>Type of pectins used</th><th>Pectin usage dosages (%)</th><th>pH</th><th>Sugar (°Brix)</th></tr></thead><tbody><tr><td colspan="6">Beverages, dairy products and analogues</td></tr><tr><td>Beverages (Acid dairy drinks)</td><td>HM</td><td>0.2 – 0.5</td><td>3.4-4.6</td><td>5–15</td><td>(Endreb & Christensen, 2020; Guo et al., 2021; Laurent & Boulenguer, 2003)</td></tr><tr><td>Beverages (yoghurt drinks)</td><td>HM</td><td>0.2–0.5</td><td>3.8–4.2</td><td>15</td><td>(Endreb & Christensen, 2020; Guo et al., 2021)</td></tr><tr><td>Dairy desserts (yoghurt)</td><td>LM</td><td>0.15–0.25</td><td>3.8–4.5</td><td>5</td><td></td></tr><tr><td>Syrup for milk desserts</td><td>ALMP</td><td>1.5</td><td>4.0–4.2</td><td>20</td><td></td></tr><tr><td colspan="6">Jams, fruit preparations, glazes, Baking stable fruit filling, jellies, confectionery and marmalades</td></tr><tr><td>Jam</td><td>HM</td><td>0.1–0.4</td><td>3.0–3.3</td><td>60–70</td><td>(Endreb & Christensen, 2020)</td></tr><tr><td>Marmalade</td><td>HM</td><td>0.1–0.4</td><td>3.0–3.3</td><td>60–70</td><td></td></tr><tr><td>Reduced sugar jam</td><td>ALMP/ LM</td><td>0.6–0.8</td><td>3.2–3.4</td><td>30–45</td><td></td></tr><tr><td>Fruit preparations</td><td>ALMP/ LM</td><td>0.5 – 0.7</td><td>3.5–4.0</td><td>40</td><td></td></tr><tr><td>Glaze</td><td>ALMP</td><td>0.8–1.2</td><td>3.4–3.6</td><td>44–65</td><td></td></tr><tr><td>Baking stable filling</td><td>HM/LM</td><td>0.6/1.2</td><td>3.0–3.6</td><td>65</td><td></td></tr><tr><td>Jelly</td><td>LM</td><td>0.7 – 1</td><td>3.4–3.6</td><td>15</td><td></td></tr><tr><td>Confectionery</td><td>ALMP/ HM</td><td>1.3–2.4</td><td>3.2–4.1</td><td>78</td><td></td></tr></tbody></table>

interaction of divalent cations with water molecules (refer to Fig. 5) and the stability and number of crosslinks that the cation can form with pectin chains (refer to Fig. 6) (Assifaoui et al., 2015; Huynh et al., 2017; Kohn, 1975; Maire du Poset, Zitolo et al., 2020). To increase the adsorption ability of pectin, a lower molecular weight and lower methoxylation are recommended. This can be achieved by alkali and enzymatic modifications that broke pectin into a shorter and reduced side-chain structures. The adsorption process of organic pollutants (dyes) by pectin mainly depends on electrostatic interactions. The free carboxyl functional groups can dissociate into $COO^-$ at pH above GalA's pKa. Therefore, organic molecules which possess positive charges ($-NH_3^+$) can be effectively removed by the pectin-based materials (Li et al., 2022). Moreover, the adsorption properties are intimately affected by external factors (pH, ionic strength, temperature, contact time, initial pollutant concentration) (Qi et al., 2021) and are related to the molecular structure of pectin. Pectin can be used as an adsorbent for removing heavy metals, however, this process is difficult to achieve since agglomeration may occur during adsorption, producing a dense cake which is difficult to filtrate (Mata, Blázquez, Ballester, González & Muñoz, 2010). This may be considered as a drawback of dissolved pectin to be used as an adsorbent in the industry. Some attempts such as preparation of pectate-based hydrogels (see Fig. 7) (chemically modified pectins) were carried out to overcome this issue. On another hand, the presence of carboxylate groups in pectin could have a positive impact on the extraction of some minerals. Indeed, it can interact with specific cations ($Al^{3+}$, $Ca^{2+}$, $Zn^{2+}$, $Fe^{3+}$, ...) located on the surfaces of some minerals (tungsten, molybdenum, ...), modifying the latter (hydrophilicity, wettability, surface energy, zeta potential, ...) and thus their floatability. Therefore, the interactions between pectin and these minerals create a difference in the floatability which later helps to separate and extract (Wang et al., 2022).

Pectin-based adsorbents have significant capacities for adsorbing toxic heavy metals, organic pollutants, and minerals for valorisation purposes. However, dissolved pectins alone have certain limitations, such as low stability, mechanical strength, and difficulties in collection after adsorption. Further research is needed to explore the relationship between the chemical structure of pectin-based adsorbents and their performance in binding heavy metals. One promising solution is the development of systems that combine magnetic iron nanoparticles with pectin chains, allowing for efficient pollutant binding and separation using magnets (Maryjose et al., 2022; Qi et al., 2021). Regarding mineral separation, pectin is more suitable for minerals with cations on their surface (such as $Ca^{2+}$ and $Mg^{2+}$) rather than negatively charged ions (such as $WO_2$) (Jiao et al., 2019). In some cases, modifying the mineral surfaces (e.g., talc and molybdenite) by depositing copper sulphate ($CuSO_4$) is necessary to enhance the adhesion of pectins to the surface (chemisorption), thereby improving the wettability and floatability of molybdenite (Wang et al., 2022).

## Interaction of pectins with other ingredients

While developing new processed food and non-food products, understanding the type and nature of interactions among food ingredients has been of great interest to academia, industry, and food formulators. The ability to create interactions and synergies through blending different biopolymers, such as pectin with other hydrocolloids, offers commercial attractiveness by enabling the design of sustainable and cost-effective products with improved textures. One significant advantage of such interactions is the potential to reduce the dosage of expensive hydrocolloids by replacing them with cheaper and safer alternatives. There are two fundamental types of interactions between biopolymers: (1) attractive interactions, where the macromolecules associate with each other in an energetically favorable manner, and (2) repulsion by steric exclusion, where the macromolecules repel and exclude each other from the space they occupy (Tolstoguzov, 2003, 2006). Depending on their chemical and macromolecular
characteristics, pectins can exhibit both types of interactions. They are known to synergistically interact with various biopolymers such as cellulose, hemicelluloses, proteins, lipids, and others.

## Interaction of pectins with polysaccharides

### Pectin – cellulose interactions

Depending on the chemical characteristics of pectins (rich or poor in neutral sugar side chains), their interactions with cellulose when mixed in aqueous media can vary. Research studies (Agoda-Tandjawa, Durand, Gaillard, Garnier & Doublier, 2012a, 2012b; Zykwinska et al., 2008; Zykwinska, Domagala, Czardybon, Pilawa & Lapkowski, 2006, 2007) have shown that pectins rich in neutral sugar side chains can bind to cellulose, while pectins poor in neutral sugar side chains do not exhibit molecular interactions with cellulose. The extent of binding between pectin and cellulose depends on the nature and structure of the neutral side chains, specifically arabinans and galactans. Electrostatic interactions or van der Waals forces are believed to be responsible for these interactions (Zykwinska et al., 2008, 2006, 2007). Multiple techniques such as rheology at small deformation, solid-state NMR, and TEM have been employed to study the interactions between cellulose and pectins. The results consistently demonstrate that no molecular interactions occur between cellulose and pectins poor in neutral sugar side chains. (Zykwinska et al., 2008, 2006, 2007). By using various physicochemical techniques (rheology at small deformation, solid-state NMR, TEM...), it was clearly shown that no molecular interactions can be established between cellulose and pectins poor in neutral sugar side chains (Agoda-Tandjawa et al., 2012a, 2012b; Zykwinska et al., 2008, 2006, 2007). To comfort these observations, Agoda-Tandjawa et al. (Agoda-Tandjawa et al., 2012a, 2012b), demonstrated that when pectin rich in neutral sugar side chains is mixed with cellulose, a synergistic gel is obtained as a result of the interactions between cellulose and pectin neutral sugar side chains, whereas an antagonistic (or anti-synergistic) effect is obtained for pectin poor in neutral sugar side chains. It was also shown that an important synergy can be obtained while mixing LM pectin with cellulose in the presence of calcium (Ca²⁺ at 3 mM for example) with or without sodium (Na⁺ at 100 mM for example) cations (Agoda-Tandjawa et al., 2012b). These results underline the important role of the Ca²⁺ ions in the incorporation and maintenance of the pectins in the cellulosic network. Microstructural analysis using CLSM and TEM revealed pectin aggregation near to the cellulose microfibrils, indicating the formation of an interpenetrating gel. (Agoda-Tandjawa et al., 2012b).

### Pectin – hemicellulose interactions

As mentioned in the previous section, the binding of hemicelluloses (specifically xyloglucans and arabinoxylans) to pectins is dependent on their chemical characteristics, and it has been observed that they bind synergistically (Zykwinska et al., 2008, 2007). These interactions involve the covalent binding of xyloglucans and arabinoxylans to pectins through ferulic acid residues, resulting in a synergistic binding effect. When different types of pectin are blended, such as low methoxy (LM) pectin, high methoxy (HM) pectin, and/or amidated low methoxy pectin (ALMP), it has been demonstrated that synergistic effects can be achieved by incorporating various sucrose contents (ranging from 30% to 60%) (Löfgren & Hermansson, 2007; Löfgren, Walkenström & Hermansson, 2002). These synergistic effects contribute to the enhanced functionalities and properties of the blended pectin systems.

### Pectin – starch interactions

The interactions between pectin chains and starch granules depend strongly on the mixing ratio of both biopolymers, the concentration, and chemical characteristics of both polysaccharides as well as the media conditions (BeMiller, 2011; Chen et al., 2022; Rojas, Rosell & Benedito de Barber, 1999; Savary, Handschin, Conde-Petit, Cayot & Doublier, 2008). It was shown that mixing starch with LM pectin can result in the

formation of synergistic mixed gels that can be modulated by added calcium and co-solute (sucrose) contents (Khondkar, Tester, Hudson, Karkalas & Morrow, 2007). However, the precise mechanisms underlying these synergistic interactions are not fully understood. Recently, it was shown that pectin can adsorb onto the surface and penetrate into starch granules when starch is pasted together with pectin and therefore enhancing starch paste viscosity through a polymer segregation mechanism (Sobska et al., 2022). Similar synergistic effects have been observed between carrageenan chains (a negatively charged sulfated polysaccharide like pectin) and starch granules, suggesting the existence of coexisting phenomena such as partial penetration of pectin into starch granules, partial exclusion of pectin by starch granules, and predominant adsorption of pectin onto starch granules, possibly influenced by osmotic pressure effects. Moreover, the electrostatic interactions between starch endogenous proteins and pectin chains cannot be excluded (Lascombes et al., 2017). Besides these observations, it was also demonstrated that covalent interactions can be created between starch granules and pectin when mixing both polysaccharides in the presence of sodium trimetaphosphate as a cross-linking agent, and then lead to strong synergistic gels with higher thermal stability through the formation of the covalent bonds (Carbinatto, de Castro, Cury, Magalhaes & Evangelista, 2012, 2014; Chen et al., 2022; Soares, de Castro, Cury & Evangelista, 2013).

### Pectin – alginate interactions

Pectin and alginate which are both negatively charged, are well-known to interact synergistically to form highly strengthened mixed gels (Sanchez-Gonzalez et al., 2021; Walkenström, Kidman, Hermanson, Rasmussen & Hoegh, 2003). Indeed, it has been largely reported that the structural properties of this type of mixed gel depend strongly on the pectin/alginate ratio, the degree of esterification of pectin and the mannuronic and guluronic acid proportions of alginate. Pectins and alginates can undergo intermolecular binding to rise coupled networks. The interaction between pectin and alginate is enhanced as the proportion of these sequences is increased. The gelation mechanism between pectin and alginate involves intermolecular junction zones formed by the union of polyvalent cations (e.g., Ca²⁺) with guluronic acid blocks of alginate or galacturonic acid residues in pectin of the adjacent polymer chains. The mixture of pectin and alginate can lead to the formation of thermoreversible gels making it one of the most interesting features of the food industry, including the preparation of cold-setting fruit gels, and stabilization of acidic emulsions like salad cream or mayonnaise. Additionally, these mixtures can be used in low sugar or calorie jams and jellies (Braccini & Perez, 2001; Sanchez-Gonzalez et al., 2021; Walkenström et al., 2003).

### Pectin – chitosan interactions

Pectin and chitosan are polysaccharides which can form poly-electrolyte complexes due to their opposite surface charge characteristics (Colodel et al., 2020; Morello et al., 2021; Shitrit & Bianco-Peled, 2021). Chitosan is a weak polybase and pectin is a weak polyacid, therefore, in the solution, this can lead to the formation of electrostatic attractions between the amino groups charged positively (-NH₄⁺) in chitosan and negatively at pectin's carboxyl groups (-COO⁻). Different interactions such as van der Waals, electrostatic, hydrophobic, hydrogen and coordination bonding may occur between these groups in pectin-chitosan complexes. It was shown that the gelation of the chitosan-pectin mixed system is thermoreversible when the pH is low (pH < 2) and when the gelling temperature is dependent on the weight ratio of the polysaccharides (Colodel et al., 2020; Morello et al., 2021; Shitrit & Bianco-Peled, 2021).

## Interaction of pectins with proteins

Depending on the structural and ionic characteristics of pectin and protein in the mixture the interactions between these two occurs
through two different mechanisms in nature either with an associative phase or segregate phase separations, (Tolstoguzov, 2003, 2006). Another type of interaction can take place between proteins and polysaccharides, such as covalent bonds, known as “conjugated, forming very stable structures. Some non-covalent interactions such as hydrophobic, hydrogen bonding and van der Waals forces could also occur between protein and polysaccharides. As discussed previously in this review, various intrinsic and extrinsic parameters have an impact over synergistic effect between pectin and proteins. In the case of gelatine, pectin can bind synergistically to gelatine to form strong mixed gels whose structural and rheological behaviours depend on various intrinsic and extrinsic parameters (Flutto, 2003; Gilsenan, Richardson & Morris, 2003). Two phenomena could explain the mechanisms behind such synergistic gel formation: the first phenomenon is the phase separation that includes two mechanisms type, the segregative (also called thermodynamic incompatibility) and the associative (also called complex coacervation) interactions. Besides the interactions between animal proteins (milk and egg proteins, for example), pectin can synergistically bound to plant proteins through hydrogen bonding, electrostatic and hydrophobic interactions (Azam et al., 2020; Einhorn-Stoll, Hatakeyama & Hatakeyama, 2012; Guo, Bayram et al., 2022). These later interactions can be advantageously used for designing plant-based foods and beverages.

### Interaction of pectins with lipids

Lipids impart various attributes to food, such as appearance, flavour, and texture properties. In high-fat foods, it is crucial to regulate lipid digestion in the small intestine. Numerous studies have reported the beneficial inhibitory effect of pectin on lipid digestion and absorption (Espinal-Ruiz, Parada-Alfonso, Restrepo-Sánchez, Narváez-Cuenca & McClements, 2014; Zhou, Bi, Chen, Wang & Richel, 2021). Pectin can influence lipid digestion through multiple mechanisms, which can be attributed to its ability to modify ion concentration and viscosity of the digestive medium. Additionally, it impacts the properties of lipid droplet surfaces and lipase activity (Cervantes-Paz et al., 2017; Espinal-Ruiz et al., 2014; Zhou et al., 2021). Notably, the flocculation of lipid droplets may be caused by the in-situ formation of calcium-pectin microgels, reducing the surface area of emulsified lipids exposed to gastrointestinal lipase. Furthermore, pectin can create an interfacial layer that surrounds lipid droplets, preventing lipase access. This allows pectin to influence the activities of digestive enzymes by either protonating their active sites or directly interacting with them (Zhou et al., 2021). It should be noted that pectin's ability to inhibit lipid digestion depends primarily on its type (nature, origin, and extraction method), composition (neutral sugar, degree of methyl esterification, etc.), and structure (branching degree, molecular weight, etc.) (Cervantes-Paz et al., 2017; Christiaens et al., 2016). Recent studies have indicated that pectin with higher molecular weight and extensively branched side chains, resulting in stronger intermolecular interactions, exhibits a more pronounced inhibitory effect on lipid digestion. These results have an important contribution over the understanding of influence of dietary fibers on lipid digestion. The control of lipid digestibility within the gastrointestinal tract could be particularly important for the development of reduced-calorie emulsion-based functional food products. (Espinal-Ruiz et al., 2014)

### Interaction of pectins with surfactants, volatile and/or phenolic compounds

The chemical and macromolecular characteristics of pectins, surfactants, volatile and/or phenolic compounds allow them to interact synergistically with each other under the presence and absence of cations such as calcium, which is also a gel promoting cation for LM pectins (Asker, Weiss & McClements, 2008; Guo, Bayram et al., 2022; Guo et al., 2020; Joshi, Rawat & Bohidar, 2016; Kim, Ju, Kim, Yoo & Kim, 2016; Li

et al., 2022).

### Interaction of pectin with surfactants

The formation of pectin-surfactant complexes has attracted significant interest as it presents an opportunity to design novel matrices for both food and non-food applications. Several studies have been conducted to explore the interactions between pectin and different types of surfactants (Asker et al., 2008; Joshi et al., 2016). These studies investigated various surfactants, including cationic surfactants (such as cetyltrimethylammonium bromide, CTAB, and dodecyl trimethylammonium bromide, DTAB, as well as Lauric arginate, LAE), anionic surfactants (sodium dodecyl sulfate, SDS), and neutral surfactants (Triton X-100, TX-100). The surfactant concentrations were maintained below and above their critical micellar concentration (CMC) at room temperature (Joshi et al., 2016).

When the surfactant concentration was kept below its CMC at room temperature, it was observed that cationic surfactants exhibited stronger interactions with pectin, both in the presence and absence of calcium chloride, compared to anionic and neutral surfactants. Despite lacking a charged headgroup, neutral surfactants still showed noticeable interaction with the polymer, while anionic surfactants exhibited weak interaction. The formation of pectin-CTAB or DTAB complexes was attributed to associative electrostatic and hydrophobic interactions. Among the cationic surfactants, CTAB displayed a strong interaction with pectin due to its long hydrocarbon chain. The morphology of the formed complexes varied, with random coil structures observed at lower surfactant concentrations and rod-like or extended random coil structures at higher concentrations. Thus, the functional characteristics of the complex could be controlled by varying the type of surfactant (charge and structure) and its concentration (Joshi et al., 2016).

Rheological measurements comparing pectin-CTAB and pectin-DTAB gels revealed differential network rigidity. The addition of a small amount of surfactant (concentration << CMC) was sufficient to enhance network strength, while larger amounts of surfactant resulted in the formation of fragile gels. Gel formation did not occur when the surfactant concentration approached its CMC value. By using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements, the interactions between cationic LAE and HM pectin were investigated. The study demonstrated that LAE bound to pectin, and the resulting complexes could be soluble or insoluble depending on the composition of the solution. The amount of LAE bound per unit of HM pectin decreased with increasing pectin concentration and temperature. The binding contribution to the LAE-pectin interaction was exothermic and attributed to electrostatic attraction between the cationic surfactant and anionic biopolymer. In addition to electrostatic interactions, hydrophobic interactions and hydrogen bonds also played a role in the formation of pectin-surfactant complexes (Asker et al., 2008). These interactions contribute to the remarkable rheological synergistic effects observed in the relevant literature. However, the specific nature of these interactions can be modulated by the surface charge characteristics of the surfactants and the conditions of the medium, as mentioned in the previous sections. Apart from binary complexes, pectin can also form ternary complexes with surfactants and other molecules, such as starches, vegetable proteins (Einhorn-Stoll et al., 2012; Guo, Bayram et al., 2022, 2022; Guo et al., 2020), milk proteins, volatile compounds, and non-starch polysaccharides, as discussed in the earlier sections.

### Interaction of pectins with volatile and phenolic compounds

Pectins are well-known to bound to aroma compounds through non-covalent interactions (hydrophobic and electrostatic) and therefore allow them to be released in specific environments (Kim et al., 2016; Li et al., 2022). Such interactions are affected by pectin's chemical and macromolecular characteristics such as D̄A, DB, DE and, Mw and others. However, the interactions between pectin and volatile compounds in food and non-food matrices during thermo-mechanical processing (at
low or high temperature) has not been fully evaluated. In fact, one can hypothesize that the processing method might strongly influence the extent of interactions between pectin and volatile compounds, which would further result in differences in the flavor release. In addition to the ingredients mentioned earlier, phenolic compounds are natural non-energetic compounds synthesized by plants, characterized by the presence of at least one aromatic ring and a hydroxyl group in their structure. These compounds are naturally bound to plant cell walls through non-covalent interactions (Sperber, Stuart, Schols, Voragen & Norde, 2009). Depending on above mentioned macromolecular characteristics of pectins, their resulting complex molecular structure confers some degree of interaction with phenolic compounds. Therefore, the extent of such non-covalent interactions could prevent the phenolic compounds from performing their antioxidant activities (Li et al., 2022).

Even though tuneable synergistic gels can be obtained while mixing properly pectin with each considered molecules (surfactants, volatile or phenolic compounds), there is still considerable work to be done in order to address clearly the role of each pectin macromolecular characteristics (such as DB, Mw, DE, DA, etc.) on resulting properties. This includes the impact of parameters such as temperature, pH, ionic strength during processing operations of food and non-food matrices, as well as the types/nature of pectins that exhibit emulsifying properties as earlier reported in section 3.3. All above mentioned binary and ternary complexes are well suitable for the encapsulation of sensitive ingredients (amino acids, vitamins). For instance, if the active component is hydrophobic, encapsulating it in a hydrophilic matrix allows for its appropriate distribution in a hydrophilic environment.

## Uses and customer applications

Pectins are used in diverse food and non-food applications thanks to their texturizing properties, sensorial behaviours, biological activities, and other key functional properties (Endreb & Christensen, 2020; Thakur et al., 1997; Voragen et al., 1995). Therefore, pectin manufacturers generally offer a wide range of pectin types for different uses and applications (see Table 1 and sections 3 and 4). In all pectin applications, its functionality is very much dependent on multiple challenging conditions that allow fully exploiting its texturizing, nutritional and health potentials. For example, among all challenging conditions, one can mention the following parameters: pH, ionic strength and composition, the proportion of sweeteners and their nature, and, where the fruit is present, the amount and nature of the pectin provided by the fruit. Besides all of these conditions, the following aspects need to be considered: the shelf-life (stability over time), the dissolution rate and the cost-in-use of the pectin as well as the target application areas where “organic” or “non-organic” claim is to be made for the product one wishes to develop. For example, in Europe, only non-amidated pectins may be used if an “organic” claim is to be made for the product. In terms of cost-in-use, any formulator targets the lowest as possible. For dissolution aspects, in most applications, it is essential to ensure that the pectin is easily and fully dissolved before gelling conditions are reached. Pectin will not dissolve when near gelling conditions, especially the HM pectins in particular will not be dissolved easily in solutions containing high amounts of sugar (> 25%) (Endreb & Christensen, 2020). To achieve good pectin dissolution, high shear mixing systems and blending pectin with sugar are often used by formulators. The usage levels of pectin could have an impact on its dissolution rate while directly pouring pectin powder into highly viscous systems containing various components and this is a big challenge for any formulator. The above-mentioned factors which influence gelation must always be kept in mind. In the most practical situations, the media conditions (sucrose and fruit contents as well as the pH) are managed properly to avoid pre-gelation issues.

As disclosed previously, the use of pectins in specific food and non-food applications requires to follow rigorously the guidelines set by the regulatory authorities considering the target need. For example, pectin could have two distinct functions in dairy products and its

analogues, the HM pectins act as protein dispersion stabilizers at reduced pH, whereas LM pectins behave quite differently and can be used to gel neutral milk desserts or as a texturiser in more acid products by interaction with calcium and milk proteins (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). For acid dairy drinks, the HM pectin is an effective protective colloid for casein or similar protein particles at a pH around 4 values, typical for the yoghurt as fully described in section 4.2. Pectin dosage and protein level in the drink as well as the size of the protein particles could strongly impact the stability of acid dairy drinks. For example, overdosing pectin for stabilization purposes will increase the viscosity of the final product, which may positively or negatively affect the texture and mouthfeel (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). The LM pectins can be used for milk jellification by directly dispersing the powder in preference priyor mixed by several times with similar amounts of sugar. In cold milk the same result is achieved by heating the milk while stirring till the boiling point to dissolve the pectin. Besides dairy products, the earliest reported application of pectin was in fruit jams with 60-70% of total soluble solids (Table 2). Depending on the nature of the fruit and the desired final soluble solids content, differing amounts and types of pectin will be required (Endreb & Christensen, 2020). Other sweet applications of pectins are jellies, marmalades and preserves (Table 2). Typically for clear jellies, the use of a slow or extra slow set pectin is required in order to allow small air bubbles to rise before the gel sets in the final container. Moreover, low sugar jams and jellies are usually prepared by LM pectins (Endreb & Christensen, 2020). For reduced sugar jams, the local regulations and requirements are to manage the preservative to be used if needed (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). The combinations of ALMP and LMP or the addition of gums (e.g. locust bean gum) are sometimes used to counteract synergesis tendency at very low soluble solids (Endreb & Christensen, 2020). The other applications of such industrial fruit preparations (e.g. traditional bakery, biscuit jams, fruit yoghurts, ...), are one of the common requirements of product stability after manufacturing (Endreb & Christensen, 2020). For glazes and spray glazes, it is equally possible to use pectin to make fully thermally reversible gels at a range of soluble solids levels, and for a glazing jelly based on LMA pectin combined with phosphate salts which control both the availability of calcium and the pH of the gel as disclosed elsewhere (Endreb & Christensen, 2020).

In some cases, a blend of pectin with other additives (e.g. starches) may be required (see section 4.1.3). In confectionery, two types of products can be designed based on different types of pectins: tender and fruity jellies made with HM pectin, and elastic jellies based on LM or ALMP blended with sequestering phosphate buffers (mint and other non-acid flavours) (Endreb & Christensen, 2020; Guo et al., 2021; Wusigale et al., 2020). It may be crucial to include a proportion of glucose syrup to prevent sugar crystallization in such confectionery applications (Endreb & Christensen, 2020). Pectin is also used in various types of dough in bread and pastry, where it improves the volume of the bread and enables moisture and softness retention during storage (Endreb & Christensen, 2020). For this application, typical pectin could be used to mimic fat-like mouthfeel by the formation of soft smooth gel particles when hydrated (Endreb & Christensen, 2020). Besides food and beverage applications, pectin can be used in other applications as well which are related to nutraceuticals, biological activities and pharmaceuticals. Several studies have attested benefits of pectin for nutritional and health aspects (Assifaoui et al., 2015; Moslemi, 2020; Naqash, Masoodi, Rather, Wani & Gani, 2017; Reichembach & Lucia de Oliveira Petkowicz, 2021) as well as in other non-food applications such as cosmetics (Massel, Fang & Corredig, 2020; Reichembach & Lucia de Oliveira Petkowicz, 2021) and organic effluents treatments (Reichembach & Lucia de Oliveira Petkowicz, 2021; Shahrin et al., 2021).
Conclusions and challenges

In this review, we have covered the overview of pectins, including their raw materials, processing, and applications in various customer applications. The processing history of pectins can impact their fine structure and key techno-functional properties, such as viscosity, stabilization, gelation, emulsification, encapsulation, film formation, and adsorption. The fine structure of pectins, which consists of the backbone and associated components, plays a crucial role in determining their functionalities. Factors like the nature of raw materials and processing conditions are closely linked to the pectin structure. Some challenges that remain in these areas include the development of user-friendly characterization methods for pectins, integration of environmentally friendly extraction techniques for industrial-scale applications, and the utilization of affordable new pectin sources in sufficient quantities for large-scale production. High molecular weight pectins are well-suited for beverage stabilization, such as emulsions and dairy products, as they increase the viscosity of the continuous phase. Pectins also prevent undesired phenomena like oil coalescence, creaming, and protein aggregation. Understanding the impact of minerals, proteins, and experimental conditions like temperature, concentration, pH, and ionic strength on the stability of food drinks is crucial for further research. Moreover, the high molecular weight and self-assembling properties of pectins make them promising candidates for edible films and coating agents that contribute to food preservation. However, improvements are needed to address limitations such as low permeability and mechanical properties of pectin films for diverse applications. The presence of ferulic acid and protein moieties in pectin allows them to absorb onto oil droplet surfaces and reduce interfacial tension, making them suitable for emulsion stabilization. However, their effectiveness as natural emulsifiers in food products are currently limited and requires further reinforcement. Optimizing pectin extraction processes to obtain desirable features such as high molecular weight, significant protein content, and degree of acetylation above 10% can enhance their performance as emulsifiers. Pectins with different degrees of esterification (HMP and LMP) have distinct gelation properties, allowing them to form gels in specific conditions. This gelation property is particularly useful for encapsulating labile molecules and controlling their release in targeted destinations. While the gelation mechanism and structure of pectin hydrogels have been extensively studied, there is a need for a better understanding and control of the impact of pectin structural variability on gelation kinetics, temperature, strength, structure, and texture under varying environmental conditions. Pectin's functional groups and ability to bind divalent cations make it a potential adsorbent for heavy metals and organic pollutants in water depollution. However, further research is required to fully explore their adsorption/desorption capabilities and recyclability as adsorbents. The association of pectins with other bio-macromolecules, such as proteins and polysaccharides, is commonly observed in final products, and understanding the interactions involved is crucial for comprehending the structure of the complexes formed. This is of great interest to academia, industrial scientists, producers, suppliers, and formulators. Overall, the techno-functional properties of pectins, whether used alone or in combination with other bio-macromolecules, are the basis for their traditional and potential applications in beverages, food, and non-food products. However, there are still challenges to overcome, and each type of pectin presents specific challenges depending on the desired customer applications. Meeting the requirements for easily manageable and desirable functionalities, such as easy water solubility even in highly viscous media, good stability over time (extended shelf-life), and low cost-in-use, remains a challenge that requires sustainable and innovative approaches through rational formulation.

CRediT authorship contribution statement

Ali Assifaoui: Writing – review & editing, Writing – original draft,

Supervision, Methodology, Conceptualization. **Gayane Hayrapetyan:**
Writing – review & editing. **Clémence Gallery:** Writing – review &
editing. **Guéba Agoda-Tandjawa:** Writing – review & editing, Writing –
original draft, Methodology, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.

References

Agoda-Tandjawa, G., Durand, S., Gaillard, C., Garnier, C., & Doublier, J. L. (2012a). Properties of cellulose/pectins composites: Implication for structural and mechanical properties of cell wall. *Carbohydrate Polymers*, *90*(2), 1081–1091.

Agoda-Tandjawa, G., Durand, S., Gaillard, C., Garnier, C., & Doublier, J. L. (2012b). Rheological behaviour and microstructure of microfibrillated cellulose suspensions/ low-methoxyl pectin mixed systems. Effect of calcium ions. *Carbohydrate Polymers*, *87*(2), 1045–1057.

Aguhon, P., Markova, V., Robitzer, M., Quignard, F., & Mineva, T. (2012). Structure of alginate gels: interaction of diuronate units with divalent cations from density functional calculations. *Biomacromolecules*, *13*(6), 1899–1907.

Aguhon, P., Robitzer, M., Habas, J. P., & Quignard, F. (2014). Influence of both cation and alginate nature on the rheological behavior of transition metal alginate gels. *Carbohydrate Polymers*, *112*(Supplement C), 525–531.

Ako, K., Nicolai, T., Durand, D., & Brotons, G. (2009). Micro-phase separation explains the abrupt structural change of denatured globular protein gels on varying the ionic strength or the pH. *Soft Matter*, 5.

Alba, K., Bingham, R. J., Gunning, P. A., Wilde, P. J., & Kontogiorgos, V. (2018). Pectin conformation in solution. *The Journal of Physical Chemistry B*, *122*(29), 7286–7294.

Alba, K., & Kontogiorgos, V. (2017). Pectin at the oil-water interface: Relationship of molecular composition and structure to functionality. *Food Hydrocolloids*, *68*, 211–218.

Ariou, F., Djamel, A., & Abderrahim, C. (2016). Physicochemical and sensory quality of yogurt incorporated with pectin from peel of Citrus sinensis. *Food Science & Nutrition*, 5.

Asker, D., Weiss, J., & McClements, D. J. (2008). Analysis of the interactions of a cationic surfactant (lauric arginate) with an anionic biopolymer (pectin): isothermal titration calorimetry, light scattering, and microelectrophoresis. *Langmuir*, *25*(1), 116–122.

Assifaoui, A., Bouyer, F., Chambin, O., & Cayot, P. (2013). Silica-coated calcium pectinate beads for colonic drug delivery. *Acta Biomaterialia*, *9*(4), 6218–6225.

Assifaoui, A., & Chambin, O. (2020). Pectin as Drug-Release Vehicle. In V. Kontogiorgos (Ed.), *Pectin: Technological and physiological properties* (pp. 189–207). Cham: Springer International Publishing.

Assifaoui, A., Chambin, O., & Cayot, P. (2011). Drug release from calcium and zinc pectinate beads: Impact of dissolution medium composition. *Carbohydrate Polymers*, *85*(2), 388–393.

Assifaoui, A., Lerbret, A., Uyen, H. T. D., Neiers, F., Chambin, O., Loupiac, C., & Cousin, F. (2015). Structural behaviour differences in low methoxy pectin solutions in the presence of divalent cations (Ca²⁺ and Zn²⁺): a process driven by the binding mechanism of the cation with the galacturonate unit. *Soft Matter*, *11*(3), 551–560.

Assifaoui, A., Loupiac, C., Chambin, O., & Cayot, P. (2010). Structure of calcium and zinc pectinate films investigated by FTIR spectroscopy. *Carbohydrate Research*, *345*(7), 929–933.

Axelos, M. A. V., & Thibault, J. F. (1991). Influence of the substituents of the carboxyl groups and of the rhamnose content on the solution properties and flexibility of pectins. *International Journal of Biological Macromolecules*, *13*(2), 77–82.

Azam, S. M. R., Ma, H., Xu, B., Devi, S., Siddique, M. A. B., Stanley, S. L., Bhandari, B., & Zhu, J. (2020). Efficacy of ultrasound treatment in the removal of pesticide residues from fresh vegetables: A review. *Trends Food Sci. Technol.*, 97, 417–432.

Banerjee, J., Singh, R., Vijayaraghavan, R., MacFarlane, D., Patti, A. F., & Arora, A. (2017). Bioactives from fruit processing wastes: Green approaches to valuable chemicals. *Food Chem*, *225*, 10–22.

Bellemjid, N., Assifaoui, A., Moussaif, A., El Abbadi, N., Mesfioui, A., & Iddar, A. (2021). Silica-coated calcium pectinate formulations for controlling carbendazim release: water and soil release studies. *Journal of Environmental Science and Health Part B-Pesticides Food Contaminants and Agricultural Wastes*, *56*(7), 613–622.

BeMiller, J. N. (2011). Pasting, paste, and gel properties of starché"hydrocolloid combinations. *Carbohydrate Polymers*, *86*(2), 386–423.

Bertz, A., Wöhl-Bruhn, S., Miethe, S., Tiersch, B., Koetz, J., Hust, M., Bunjes, H., & Menzel, H. (2013). Encapsulation of proteins in hydrogel carrier systems for controlled drug delivery: Influence of network structure and drug size on release rate. *Journal of Biotechnology*, *163*(2), 243–249.

Bodart, P. R., Fouilloux, P., Rachocki, A., Lerbret, A., Karbowiak, T., & Assifaoui, A. (2022). Slow water dynamics in polygalacturonate hydrogels revealed by NMR
relaxometry and molecular dynamics simulation. *Carbohydrate Polymers*, **298**, Article 120093.

Bonnin, E., Garnier, C., & Ralet, M. C. (2014). Pectin-modifying enzymes and pectin-derived materials: Applications and impacts. *Applied Microbiology and Food Technology*, **98**(2), 519-532.

Borgogna, M., Skjåk-Bræk, G., Paoletti, S., & Donati, I. (2013). On the initial binding of alginate by calcium ions. The tilted Egg-Box hypothesis. *The Journal of Physical Chemistry B*, **117**(24), 7277-7282.

Braccini, I., & Perez, S. (2001). Molecular basis of Ca²⁺-Induced gelation in alginates and pectins: The egg-box model revisited. *biomacromolecules*, **2**(4), 1089-1096.

Brijwani, K., & Mutilangi, W. (2021). Mouthfeel modulation in reduced and sugar-free beverages using a blend of pectin and xanthan gum. (Vol. 11812772). Purchase, NY: US: PepsiCo, Inc.

Caccavo, D., Ström, A., Larsson, A., & Lamberti, G. (2016). Modeling capillary formation in calcium and copper alginate gels. *Materials Science & Engineering: C: Biomimetic and Supramolecular Systems*, **58**, 442-449.

Cakmak, H., & Sogut, E. (2020). Functional biobased composite polymers for food packaging applications. In T. J. Gutiérrez (Ed.), *Reactive and functional polymers volume one : biopolymers, polyesters, polyurethanes, resins and silicones* (pp. 95-136). Cham: Springer International Publishing.

Cao, J., Yang, J., Wang, Z., Lu, M., & Yue, K. (2020). Modified citrus pectins by UV/H2O2 oxidation at acidic and basic conditions: Structures and in vitro anti-inflammatory, anti-proliferative activities. *Carbohydrate Polymers*, **247**, Article 116742.

Cao, L., Lu, W., Mata, A., Nishinari, K., & Fang, Y. (2020). Egg-box model-based gelation of alginate and pectin: A review. *Carbohydrate Polymers*, **242**, Article 116389.

Cao, Y., Li, S., Fang, Y., Nishinari, K., Phillips, G. O., Lerbret, A., & Assifaoui, A. (2018). Specific binding of trivalent metal ions to λ-carrageenan. *International Journal of Biological Macromolecules*, **109**, 350-356.

Capel, F., Nicolai, T., Durand, D., Boulenguer, P., & Langendorff, V. (2006). Calcium and acid induced gelation of (amidated) low methoxyl pectin. *Food Hydrocolloids*, **20**(6), 901-907.

Carbinatto, F. M., de Castro, A. D., Cury, B. S. F., Magalhaes, A., & Evangelista, R. C. (2012). Physical properties of pectin-high amylose starch mixtures cross-linked with sodium trimetaphosphate. *International Journal of Pharmaceutics*, **423**(2), 281-288.

Carbinatto, F. M., de Castro, A. D.r., Evangelista, R. C., & Cury, B. S. F. (2014). Insights into the swelling process and drug release mechanisms from cross-linked pectin/high amylose starch matrices. *Asian Journal of Pharmaceutical Sciences*, **9**(1), 27-34.

Cargill, UniPECTINE® Pectin's "a-peeling" future. (2022). https://www.cargill.com/doc/1432212800659/pectin-ingredient-iq.doc.pdf Accessed.

Cargin, M. A., Gasparin, B. C., dos Santos Rosa, D., & Paulino, A. T. (2021). Performance of lactose encapsulated in pectin-based hydrogels during lactose hydrolysis reactions. *LWT*, **150**, Article 111863.

Celus, M., Kyomugasho, C., Van Loey, A. M., Grauwet, T., & Hendrickx, M. E. (2018). Influence of pectin structural properties on interactions with divalent cations and its associated functionalities. *Comprehensive Reviews In Food Science and Food Safety*, **17**(6), 1576-1594.

Cervantes-Paz, B., Ornelas-Paz, J. J., Ruiz-Cruz, S., Rios-Velasco, C., Ibarra-Junquera, V., Yahia, E. M., & Gardea-Béjar, A. A. (2017). Effects of pectin on lipid digestion and possible implications for carotenoid bioavailability during pre-absorptive stages: A review. *Food Research International*, **99**(Pt 2), 917-927.

Chan, S. Y., Choo, W. S., Young, D. J., & Loh, X. J. (2017). Pectin as a rheology modifier: Origin, structure, commercial production and rheology. *Carbohydrate Polymers*, **161**, 118-139.

Chen, R., Williams, P. A., Shu, J., Luo, S., Chen, J., & Liu, C. (2022). Pectin adsorption onto and penetration into starch granules and the effect on the gelatinization process and rheological properties. *Food Hydrocolloids*, **129**, Article 107618.

Christiaens, S., Van Buggenhout, S., Houben, K., Jamsazadeh Kermani, Z., Moelants, K. R. N., Ngouémazong, E. D., Van Loey, A., & Hendrickx, M. E. G. (2016). *Process-Structure-Function relations of pectin in food. Critical Reviews in Food Science and Nutrition*, **56**(6), 1021-1042.

Ciriminna, R., Albanese, L., Meneguzzo, F., & Pagliaro, M. (2021). IntegroPectin: A new citrus pectin with uniquely high biological activity. *Biology and Life Sciences Forum*, **6**(1), 76.

Ciriminna, R., Fidalgo, A., Scurria, A., Ilharco, L. M., & Pagliaro, M. (2022). Pectin: New science and forthcoming applications of the most valued hydrocolloid. *Food Hydrocolloids*, **127**, Article 107483.

Colodel, C., Vriesmann, L. C., Teófilo, R. F., & de Oliveira Petkowicz, C. L. (2020). Optimization of acid-extraction of pectic fraction from grape (Vitis vinifera cv. Chardonnay) pomace, A Winery Waste. *International Journal of Biological Macromolecules*, **161**, 204-213.

Cooper, C., Dubin, P. L., Kayitmazer, A. B., & Turksen, S. (2005). Polyelectrolyte-protein complexes. *Current Opinion in Colloid & Interface Science*, **10**, 52-78.

Cui, J., Zhao, C., Feng, L., Han, Y., Du, H., Xiao, H., & Zheng, J. (2021). Pectins from fruits: Relationships between extraction methods, structural characteristics, and functional properties. *Trends in Food Science & Technology*, **110**, 39-54.

Da Silva, J. L., & Rao, M (2006). Pectins: structure, functionality, and uses. *Food polysaccharides and their applications*, 353.

Das, I., & Arora, A. (2021). Kinetics and mechanistic models of solid-liquid extraction of pectin using advance green techniques- a review. *Food Hydrocolloids*, **120**, Article 106931.

Dhalleine, C., Assifaoui, A., Moulari, B., Pellequer, Y., Cayot, P., Lamprecht, A., & Chambin, O. (2011). Zinc-pectinate beads as an in vivo self-assembling system for pulsatile drug delivery. *International Journal of Pharmaceutics*, **414**(1), 28-34.

Donati, I., Asaro, F., & Paoletti, S. (2009). Experimental evidence of counterion affinity in alginates: The case of nongelling ion Mg²⁺. *Journal of Physical Chemistry B*, **113**(39), 12877-12886.

Donati, I., Benegas, J. C., & Pauletti, S. (2006). Polyelectrolyte study of the calcium-induced chain association of pectate. *Biomacromolecules*, **7**(12), 3439-3447.

Dupont, C., & Vandenplas, Y. (2020). Different thickening complexes with pectin in infant anti-regurgitation formula. *Acta Paediatrica*, **109**(3), 471-480.

Einhorn-Stoll, U., Hatakeyama, H., & Hatakeyama, T. (2012). Influence of pectin modification on water binding properties. *Food Hydrocolloids*, **27**(2), 494-502.

Endreb, H. U., & Christensen, S. H (2020). Pectins. In G. O. Philips, & P. A. Williams (Eds.), *Handbook of hydrocolloids* (pp. 274-297). Cambridge: Woodhead Publishing Limited.

Espinal-Ruiz, M., Parada-Alfonso, F., Restrepo-Sánchez, L. P., Narváez-Cuenca, C. E., & McClements, D. J. (2014). Interaction of a dietary fiber (pectin) with gastrointestinal components (bile salts, calcium, and lipase): a calorimetry, electrophoresis, and turbidity study. *Journal of Agricultural and Food Chemistry*, **62**(52), 12620-12630.

Fang, Y., Al-Assaf, S., Phillips, G. O., Nishinari, K., Funami, T., & Williams, P. A. (2008). Binding behavior of calcium to polyuronates: Comparison of pectin with alginate. *Carbohydrate Polymers*, **72**(2), 334-341.

Fang, Y., Al-Assaf, S., Phillips, G. O., Nishinari, K., Funami, T., Williams, P. A., & Li, L. (2007). Multiple steps and critical behaviors of the binding of calcium to alginate. *The Journal of Physical Chemistry B*, **111**(10), 2456-2462.

Flutto, L. (2003). PECTIN | properties and determination. Ed. In B. Caballero (Ed.), *Encyclopedia of food sciences and nutrition (Second edition)* (pp. 4440-4449). Oxford: Academic Press

Fraeye, I., Colle, I., Vandevenne, E., Duvetter, T., Van Buggenhout, S., Moldenaers, P., Van Loey, A., & Hendrickx, M. (2010). Influence of pectin structure on texture of pectin-calcium gels. *Innovative Food Science & Emerging Technologies*, **11**(2), 401-409.

Fraeye, I., Duvetter, T., Dounga, E., Van Loey, A., & Hendrickx, M. (2010). Fine-tuning the properties of pectin-calcium gels by control of pectin fine structure, gel composition and environmental conditions. *Trends in Food Science & Technology*, **21**(5), 219-228.

Fu, C., Li, Z., Sun, Z., & Xie, S. (2021). A review of salting-out effect and sugaring-out effect: driving forces for novel liquid-liquid extraction of biofuels and biochemicals. *Frontiers of Chemical Science and Engineering*, **15**(4), 854-871.

Gallery, C., Agoda-Tandjawa, G., Bekaert, D., & Gitto, L. (2024). Understanding structure/rheology relationships of amidated low-methoxyl citrus and apple pectin gels: Implications of sucrose, pectin types and characteristics. *Food Hydrocolloids*, **152**, Article 109950.

Garnier, C., Axelos, M. A. V., & Thibault, J. F. (1993). Phase diagrams of pectin-calcium systems: Influence of pH, ionic strength, and temperature on the gelation of pectins with different degrees of methylation. *Carbohydrate Research*, **240**, 219-232.

Georgiev, Y., Ognyanov, M., Yanakieva, I., Kussovski, V., & Kratchanova, M. (2013). Isolation, characterization and modification of citrus pectins. *Journal of Bioscience and Biotechnology*, **2012**, 223-233.

Gilsenan, P. M., Richardson, R. K., & Morris, E. R. (2000). Thermally reversible acid-induced gelation of low-methoxyl pectin. *Carbohydrate Polymers*, **41**(4), 339-349.

Gilsenan, P. M., Richardson, R. K., & Morris, E. R. (2003). Associative and segregative interactions between gelatin and low-methoxyl pectin: Part 1. Associative interactions in the absence of Ca²⁺. *Food Hydrocolloids*, **17**(6), 723-737.

Günchedi, P., Conte, U., Chetoni, P., & Saettone, M. F. (1999). Pectin microspheres as ophthalmic carriers for piroxamic: evaluation in vitro and in vivo in albino rabbits. *European Journal of Pharmaceutical Sciences*, **9**(1), 1-7.

Grant, G. T., Morris, E. R., Rees, D. A., Smith, A. M., & Tho, D. (1973). Biological interactions between polysaccharides and divalent cations: the egg-box model. *Fehs Letters*, **32**, 195-198.

Guillotin, S. E., Bakx, E. J., Boulenguer, P., Schols, H. A., & Voragen, A. G. J. (2007). Determination of the degree of substitution, degree of amidation and degree of blockiness of commercial pectins by using capillary electrophoresis. *Food Hydrocolloids*, **21**(3), 444-451.

Guimaraes, G. C., Coelho Júnior, M. C., & Garcia Rojas, E. E. (2009). Density and kinematic viscosity of pectin aqueous solution. *Journal of Chemical & Engineering Data*, **54**(2), 662-667.

Guo, Q., Bayram, I., Shu, X., Su, J., Liao, W., Wang, Y., & Gao, Y. (2022). Improvement of stability and bioaccessibility of I²⁻-carotene by curcumin in pea protein isolate-based complexes-stabilized emulsions: Effect of protein complexation by pectin and small molecular surfactants. *Food Chemistry*, **367**, Article 130726.

Guo, Q., Su, J., Shu, X., Yuan, F., Mao, L., & Gao, Y. (2020). Development of high methoxyl pectin-surfactant-pea protein isolate ternary complexes: Fabrication, characterization and delivery of resveratrol. *Food Chemistry*, **321**, Article 126706.

Guo, Y., Wei, Y., Cai, Z., Hou, B., & Zhang, H. (2021). Stability of acidified milk drinks induced by various polysaccharide stabilizers: A review. *Food Hydrocolloids*, **118**, Article 106814.

Han, W., Meng, Y., Hu, C., Dong, G., Qu, Y., Deng, H., & Guo, Y. (2017). Mathematical model of Ca²⁺ concentration, pH, pectin concentration and soluble solids (sucrose) on the gelation of low methoxyl pectin. *Food Hydrocolloids*, **6**, 37-48.

Hayrapetyan, G., Trchounian, K., Buon, L., Noret, L., Pinel, B., Lagrue, J., & Assifaoui, A. (2023). Sequential extraction of high-value added molecules from grape pomaces using supercritical fluids with water as a co-solvent. *RSC Sustainability*, **1**(8), 2014-2023.

Hellin, P., Ralet, M. C., Bonnin, E., & Thibault, J. F. (2005). Homogalacturonans from lime pectins exhibit homogeneous charge density and molar mass distributions. *Carbohydrate Polymers*, **60**(3), 307-317.

Heumann, A., Assifaoui, A., Da Silva Barreira, D., Thomas, C., Briandet, R., Laurent, J., Beney, L., Lapaquette, P., Guzzo, J., & Rieu, A. (2020). Intestinal release of biofilm-like microcolonies encased in calcium-pectinate beads increases probiotic properties of Lacticaseibacillus paracasei. *Npj Biofilms and Microbiomes*, **6**(1), 44.
Hills, B. P., Godward, J., Debatty, M., Barras, L., Satario, C. P., & Ouwerx, C. (2000). NMR studies of calcium induced alginate gelation. Part II. The internal bead structure. *Magnetic Resonance in Chemistry*, 38(9), 719–728.

Huang, J., Hu, Z., Hu, L., Li, G., Yao, Q., & Hu, Y. (2021). Pectin-based active packaging: A critical review on preparation, physical properties and novel application in food preservation. *Trends in Food Science & Technology, 118*, 167–178.

Huynh, U. T. D., Assifaoui, A., & Chambin, O. (2017). Pellets based on polyuronates: Relationship between gelation and release properties. *Journal of Food Engineering, 199*, 27–35.

Huynh, U. T. D., Chambin, O., du Poset, A. M., & Assifaoui, A. (2018). Insights into gelation kinetics and gel front migration in cation-induced polysaccharide hydrogels by viscoelastic and turbidity measurements: Effect of the nature of divalent cations. *Carbohydrate Polymers, 190*, 121–128.

Jamsazadeh Kermani, Z., Shpgelman, A., Kyomugasho, C., Van Buggenhout, S., Ramezani, M., Van Loey, A. M., & Hendrickx, M. E. (2014). The impact of extraction with a chelating agent under acidic conditions on the cell wall polymers of mango peel. *Food Chemistry, 161*, 199–207.

Janrawut, P., Assifaoui, A., & Chambin, O. (2013). Influence of low methoxyl pectin gel textures and in vitro release of rutin from calcium pectate beads. *Carbohydrate Polymers, 97(2)*, 335–342.

Jiao, F., Dong, L., Qin, W., Liu, W., & Hu, C. (2019). Flotation separation of schelinite from calcite using pectin as depressant. *Minerals Engineering, 136*, 120–128.

Joshi, N., Rawat, K., & Bohidar, H. B. (2016). Influence of structure, charge, and concentration on the pectin–calcium–surfactant complexes. *The Journal of Physical Chemistry B, 120(18)*, 42494–4257.

Kalathaki, I., Alba, K., Muhamedsalih, H., & Kontogiorgos, V. (2019). Fabrication and characterization of metal-doped pectin films. *Food Hydrocolloids, 92*, 259–266.

Khedmat, L., Izadi, A., Mofid, V., & Mojtabehdi, S. Y. (2020). Recent advances in extracting pectin by single and combined ultrasound techniques: A review of techno-functional and bioactive health-promoting aspects. *Carbohydrate Polymers, 229*, Article 115474.

Khondkar, D., Tester, R. F., Hudson, N., Karkalas, J., & Morrow, J. (2007). Rheological behaviour of uncross-linked and cross-linked gelatinised waxy maize starch with pectin gels. *Food Hydrocolloids, 21(8)*, 1296–1301.

Kim, M. J., Ju, H. K., Kim, Y., Yoo, S. H., & Kim, Y. S. (2016). Effects of amidation and/or methylesterification of pectin on aroma release at different calcium concentration. *Food Hydrocolloids, 52*, 343–349.

Kohn, R. (1975). Ion binding on polyuronates—Alginate and pectin. *Pure and Applied Chemistry, 42*, 371–397.

Kumar, A., & Chauhan, G. S. (2010). Extraction and characterization of pectin from apple pomace and its evaluation as lipase (steapsin) inhibitor. *Carbohydrate Polymers, 82* (2), 454–459.

Kurita, O., Fujiwara, T., & Yamazaki, E. (2008). Characterization of the pectin extracted from citrus peel in the presence of citric acid. *Carbohydrate Polymers, 74(3)*, 725–730.

Ladaniya, M. (2023). Chapter 1 - introduction. In M. Ladaniya (Ed.), *Citrus fruit (Second edition)* (pp. 1–21). Academic Press.

Lascombes, C., Agoda-Tandjawa, G., Boulenguer, P., Le Garnec, C., Gilles, M., Mauduit, S., Barey, P., & Langendorff, V. (2017). Starch-carrageenan interactions in aqueous media: Role of each polysaccharide chemical and macromolecular characteristics. *Food Hydrocolloids, 66*, 176–189.

Laurent, M. A., & Boulenguer, P. (2003). Stabilization mechanism of acid dairy drinks (ADD) induced by pectin. *Food Hydrocolloids, 17(4)*, 445–454.

Lazaridou, A., & Biliaderis, C. G. (2020). Edible films and coatings with pectin. Ed. In V. Kontogiorgos (Ed.), *Pectin: technological and physiological properties* (pp. 99–123). Cham: Springer International Publishing

Li, D.-q., Li, J., Dong, H.-l., Li, X., Zhang, J.-q., Ramaswamy, S., & Xu, F. (2021). Pectin in biomedical and drug delivery applications: A review. *International Journal of Biological Macromolecules, 185*, 49–65.

Li, J., Yang, Z.-l., Ding, T., Song, Y. J., Li, H. C., Li, D.-q., Chen, S., & Xu, F. (2022). The role of surface functional groups of pectin and pectin-based materials on the adsorption of heavy metal ions and dyes. *Carbohydrate Polymers, 276*, Article 118789.

Li, L., Fang, Y., Vreeker, R., Appelqvist, I., & Mendes, E. (2007). Reexamining the egg-box model in calcium-alginate gels with X-ray diffraction. *Biomacromolecules, 8(2)*, 464–468.

Li, L., Gao, X., Liu, J., Chitrakar, B., Wang, B., & Wang, Y. (2021). Hawthorn pectin: Extraction, function and utilization. *Current Research in Food Science, 4*, 429–435.

Liew, S. Q., Teoh, W. H., Tan, C. K., Yusoff, R., & Ngoh, G. C. (2018). Subcutaneous water extraction of low methoxyl pectin from pomelo (Citrus grandis (L.) Osbeck) peels. *International Journal of Biological Macromolecules, 116*, 128–135.

Löfgren, C., & Hermansson, A. M. (2007). Synergistic rheological behaviour of mixed HM/LM pectin gels. *Food Hydrocolloids, 21(3)*, 480–486.

Löfgren, C., Walkenström, P., & Hermansson, A. M. (2002). Microstructure and rheological behavior of pure and mixed pectin gels. *Biomacromolecules, 3(6)*, 1144–1153.

Lootens, D., Capel, F., Durand, D., Nicolai, T., Boulenguer, P., & Langendorff, V. (2003). Influence of pH, Ca concentration, temperature and amidation on the gelation of low methoxyl pectin. *Food Hydrocolloids, 17(3)*, 237–244.

Lopez-Sanchez, P., Assifaoui, A., Cousin, F., Moser, J., Bonilla, M. R., & Ström, A. (2022). Impact of Glucose on the Nanostructure and Mechanical Properties of Calcium-Alginate Hydrogels. *Gels, 8(2)*.

Maire du Poset, A., Börjesson, M., Rameau, C., Madeleine-Perdrillat, C., Lerbret, A., Loupiac, C., Cousin, F., & Assifaoui, A. (2020). Controlled Loading and Release of Beta-Lactoglobulin in Calcium-Polygalacturonate Hydrogels. *Biomacromolecules, 21* (4), 1417–1426.

Maire du Poset, A., Lerbret, A., Boué, F., Zitolo, A., Assifaoui, A., & Cousin, F. (2019). Tuning the Structure of Galacturonate Hydrogels: External Gelation by Ca, Zn, or Fe Cationic Cross-Linkers. *Biomacromolecules, 20*(7), 2864–2872.

Maire du Poset, A., Zitolo, A., Cousin, F., Assifaoui, A., & Lerbret, A. (2020). Evidence for an egg-box-like structure in iron(ii)-polygalacturonate hydrogels: a combined EXAFS and molecular dynamics simulation study. *Physical Chemistry Chemical Physics*.

Martinsen, A., Skjåk-Bræk, G., & Smidsrød, O. (1989). Alginate as immobilization material: I. Correlation between chemical and physical properties of alginate gel beads. *Biotechnology and Bioengineering, 33*(1), 79–89.

Maryjose, N., Custovic, I., Chaabane, L., Lesniewska, E., Piétremont, O., Chambin, O., & Assifaoui, A. (2022). Core-shell polygalacturonate magnetic iron oxide nanoparticles: Synthesis, characterization, and functionalities. *International Journal of Biological Macromolecules, 220*, 360–370.

Massel, V., Fang, Y., & Corredig, M. (2020). Pectin nanoemulsions in multiple emulsions: Stability and encapsulation efficiency. *Food Research International, 139*, Article 109950.

Mata, Y. N., Blázquez, M. L., Ballester, A., González, F., & Muñoz, J. A. (2010). Studies on sorption, desorption, regeneration and reuse of sugar-beet pectin gels for heavy metal removal. *Journal of Hazardous Materials, 178*(1), 243–248.

May, C. D. (1990). Industrial pectins: Sources, production and applications. *Carbohydrate Polymers, 12*(1), 79–99.

Mendez, D. A., Fabra, M. J., MartAnez-Abad, A., IwartAnez-Sanz, I., Gorria, M., & LA³pez-Rubio, A (2021). Understanding the different emulsification mechanisms of pectin: Comparison between watermelon rind and two commercial pectin sources. *Food Hydrocolloids, 120*, Article 106957.

Minjares-Fuentes, R., Femenia, A., Garau, M. C., Meza-Velázquez, J. A., Simal, S., & Rosselló, C. (2014). Ultrasound-assisted extraction of pectins from grape pomace using citric acid: A response surface methodology approach. *Carbohydrate Polymers, 106*, 179–189.

Mórch, Ý. A., Donati, I., & Strand, B. L. (2006). Effect of Ca²⁺, Ba²⁺, and Sr²⁺ on alginate microbeads. *Biomacromolecules, 7*(5), 1471–1480.

Morello, G., Quarta, A., Gaballo, A., Moroni, L., Gigli, G., Polini, A., & Gervaso, F. (2021). A thermo-sensitive chitosan/pectin hydrogel for long-term tumor spheroid culture. *Carbohydrate Polymers, 274*, Article 118633.

Morris, G. A., & Ralet, M. C. (2012). The effect of neutral sugar distribution on the dilute solution conformation of sugar beet pectin. *Carbohydrate Polymers, 88*(4), 1488–1491.

Moslemi, M. (2020). Reviewing the recent advances in application of pectin for technical and health promotion purposes: From laboratory to market. *Carbohydrate Polymers, 254*, Article 117324.

Mousa, R. M. A. (2020). Simultaneous development of cloud stability and antioxidant preservation in cloudy guava juice using hydrocolloid combinations. *International Food Research Journal, 27*, 762–774.

Naqash, F., Masoodi, F. A., Rather, S. A., Wani, S. M., & Gani, A. (2017). Emerging concepts in the nutraceutical and functional properties of pectin—A Review. *Carbohydrate Polymers, 168*, 227–239.

Nastasi, J. R., Kontogiorgos, V., Daygon, V. D., & Fitzgerald, M. A. (2022). Pectin-based films and coatings with plant extracts as natural preservatives: A systematic review. *Trends in Food Science & Technology, 120*, 193–211.

Neckebroeck, B., Verkempinck, S. H. E., Bernaerts, T., Verheyen, D., Hendrickx, M. E., & Van Loey, A. M. (2021). Investigating the role of the different molar mass fractions of a pectin rich extract from onion towards its emulsifying and emulsion stabilizing potential. *Food Hydrocolloids, 117*, Article 106735.

Neckebroeck, B., Verkempinck, S. H. E., Vaes, G., Wouters, K., MagnAèe, J., Hendrickx, M. E., & Van Loey, A. M. (2019). Advanced insight into the emulsifying and emulsion stabilizing capacity of carrot pectin subdomains. *Food Hydrocolloids, 102*, Article 105594.

Neckebroeck, B., Verkempinck, S. H. E., Van Audenhove, J., Bernaerts, T., de Wilde d'Estmael, H., Hendrickx, M. E., & Van Loey, A. M. (2020). Structural and emulsion stabilizing properties of pectin rich extracts obtained from different botanical sources. *Food Research International, 141*, Article 110087.

Ngouémazong, E. D., Christiaens, S., Shpgelman, A., Van Loey, A., & Hendrickx, M. (2015). The Emulsifying and Emulsion-Stabilizing Properties of Pectin: A Review. *Comprehensive Reviews in Food Science and Food Safety, 14*(6), 705–718.

Noreen, A., Nazli, Z.-I.-H., Akram, J., Rasul, I., Mansha, A., Yaqoob, N., Iqbal, R., Tabasum, S., Zuber, M., & Zia, K. M. (2017). Pectins functionalized biomaterials; a new viable approach for biomedical applications: A review. *International Journal of Biological Macromolecules, 101*, 254–272.

Norziah, M. H., Foo, S. L., & Karim, A. A. (2006). Rheological studies on mixtures of agar (Gracilaria changii) and κ-carrageenan. *Food Hydrocolloids, 20*(2), 204–217.

Pagliaro, M., Ciriminna, R., Fidalgo, A., Delisi, R., & Ilharco, L. (2016). Pectin production and global market. *Agro Food Industry Hi Tech, 27*.

Panahirad, S., Dadpour, M., Peighambardoust, S. H., Soltanzadeh, M., Gullón, B., Alirezalu, K., & Lorenzo, J. M. (2021). Applications of carboxymethyl cellulose- and pectin-based active edible coatings in preservation of fruits and vegetables: A review. *Trends in Food Science & Technology, 110*, 663–673.

Plazinski, W. (2011). Molecular basis of calcium binding by polygalacturonate chains. Revising the egg-box model. *Journal of Computational Chemistry, 32*(14), 2988–2995.

Potter, K., Balcom, B. J., Carpenter, T. A., & Hall, L. D. (1994). The gelation of sodium alginate with calcium ions studied by magnetic resonance imaging (MRI). *Carbohydrate Research, 257*(1), 117–126.

Powell, D. A., Morris, E. R., Gidley, M. J., & Rees, D. A. (1982). Conformations and interactions of pectins: II. Influence of residue sequence on chain association in calcium pectate gels. *Journal of Molecular Biology, 155*(4), 517–531.
Prakash Maran, J., Sivakumar, V., Thirugnanasambandham, K., & Sridhar, H. (2014). Microwave assisted extraction of pectin from waste Citrullus lanatus fruit rinds. *Carbohydrate Polymers, 101*, 786-791.

Protte, K., Weiss, J., Hinrichs, J., & Knaapila, A. (2019). Thermally stabilised whey protein-pectin complexes modulate the thermodynamic incompatibility in hydrocolloid matrices: A feasibility-study on sensory and rheological characteristics in dairy desserts. *LWT, 105*, 336-343.

Qi, X., Lin, L., Shen, L., Li, Z., Qin, T., Qian, Y., Wu, X., Wei, X., Gong, Q., & Shen, J. (2019). Efficient Decontamination of Lead Ions from Wastewater by Salecan Polysaccharide-Based Hydrogels. *ACS Sustainable Chemistry & Engineering, 7*(12), 11014-11023.

Qi, X., Liu, R., Chen, M., Li, Z., Qin, T., Qian, Y., Zhao, S., Liu, M., Zeng, Q., & Shen, J. (2019). Removal of copper ions from water using polysaccharide-constructed hydrogels. *Carbohydrate Polymers, 209*, 101-110.

Qi, X., Tong, X., Pan, W., Zeng, Q., You, S., & Shen, J. (2021). Recent advances in polysaccharide-based adsorbents for wastewater treatment. *Journal of Cleaner Production, 135*, Article 128221.

Ralet, M. C., Crépeau, M. J., & Bonnin, E. (2008). Evidence for a blockwise distribution of acetyl groups onto homogalacturonans from a commercial sugar beet (Beta vulgaris) pectin. *Phytochemistry, 69*(9), 1903-1909.

Ralet, M. C., Lerouge, P., & Quemener, B. (2009). Mass spectrometry for pectin structure analysis. *Carbohydrate Research, 344*(14), 1798-1807.

Rehman, A., Ahmad, T., Aadil, R. M., Spotti, M. J., Bakry, A. M., Khan, I. M., Zhao, L., Riaz, T., & Tong, Q. (2019). Pectin polymers as wall materials for the nano-encapsulation of bioactive compounds. *Trends in Food Science & Technology, 90*, 35-46.

Rehman, Z. U., Salariya, A. M., Habib, F., & Shah, W. H. (2004). Utilization of mango peels as a source of pectin. *Journal of the Chemical Society of Pakistan, 26*, 73-76.

Reichembach, L. H., & Lucia de Oliveira Petkowicz, C. (2021). Pectins from alternative sources and uses beyond sweets and jellies: An overview. *Food Hydrocolloids, 118*, Article 106824.

Rojas, J. A., Rosell, C. M., & Benedito de Barber, C. (1999). Pasting properties of different wheat flour-hydrocolloid systems. *Food Hydrocolloids, 13*(1), 27-33.

Ropartz, D., & Ralet, M. C. (2020). Pectin Structure. In V. Kontogiorgos (Ed.), *Pectin: technological and physiological properties*. Springer.

Rubinstein, M., & Colby, R. H. (2003). *Polymer physics*. Oxford: OUP Oxford.

Ruffin, E., Schmit, T., Lafitte, G., Dollat, J. M., & Chambin, O. (2014). The impact of whey protein preheating on the properties of emulsion gel bead. *Food Chemistry, 151* (0), 324-332.

Sanchez-Gonzalez, L., Elkhoury, K., Kahn, C., Arab-Tehrany, E., Giri, T. K., & Ghosh, B. (2021). Composite hydrogels of pectin and alginate. *Plant and algal hydrogels for drug delivery and regenerative medicine* (pp. 507-533). Woodhead Publishing.

Santos, J. D. G., Espeleta, A. F., Branco, A., & de Assis, S. A. (2013). Aqueous extraction of pectin from sisal waste. *Carbohydrate Polymers, 92*(2), 1997-2001.

Savary, G., Handschin, S., Conde-Petit, B., Cayot, N., & Doublier, J. L. (2008). Structure of polysaccharide-starch composite gels by rheology and confocal laser scanning microscopy: Effect of the composition and of the preparation procedure. *Food Hydrocolloids, 22*(4), 520-530.

Secchi, E., Munarin, F., Alaimo, M. D., Bosisio, S., Buzzaccaro, S., Ciccarella, G., Vergaro, V., Petrini, P., & Piazza, R. (2014). External and internal gelation of pectin solutions: microscopic dynamics versus macroscopic rheology. *Journal of Physics: Condensed Matter, 26*(46), Article 464106.

Seisun, D., & Zalesny, N. (2021). Strides in food texture and hydrocolloids. *Food Hydrocolloids, 117*, Article 106575.

Shahrin, E. W. E. S., Narudin, N. A. H., Padmosoedarso, K. M., Kusrini, E., Mahadi, A. H., Shahri, N. N. M., & Usman, A. (2021). Pectin derived from pomelo pith as a superior adsorbent to remove toxic Acid Blue 25 from aqueous solution. *Carbohydrate Polymer Technologies and Applications, 2*, Article 100116.

Shitrit, Y., & Bianco-Peled, H. (2021). Insights into the formation mechanisms and properties of pectin hydrogel physically cross-linked with chitosan nanogels. *Carbohydrate Polymers, 269*, Article 118274.

Soares, G. A., de Castro, A. D., Cury, B. S. F., & Evangelista, R. C. (2013). Blends of cross-linked high amylose starch/pectin loaded with diclofenac. *Carbohydrate Polymers, 91* (1), 135-142.

Sobska, J., Andreiuk, B., Aparin, I. O., Reisch, A., Krezel, W., & Klymchenko, A. S. (2022). Counterion-insulated near-infrared dyes in biodegradable polymer nanoparticles for in vivo imaging. *Nanoscale Advances, 4*(1), 39-48.

Sperber, B. L. H. M., Stuart, M. A. C., Schols, H. A., Voragen, A. G. J., & Norde, W. (2009). Binding of beta-lactolobulin to pectins varying in their overall and local charge density. *Biomacromolecules, 10*(12), 3246-3252.

Suhag, R., Kumar, N., Petkoska, A. T., & Upadhyay, A. (2020). Film formation and deposition methods of edible coating on food products: A review. *Food Research International, 136*, Article 109582.

Swamy, G. J., & Muthukumarappan, K. (2017). Optimization of continuous and intermittent microwave extraction of pectin from banana peels. *Food Chemistry, 220*, 108-114.

Thakur, B. R., Singh, R. K., & Handa, A. K. (1997). Chemistry and uses of pectin - A review. *Critical Reviews in Food Science and Nutrition, 37*(1), 47-73.

Thibault, J., & Ralet, M. (2003). Physico-Chemical properties of pectins in the cell walls and after extraction. In F. Voragen, H. Schols, & R. Visser (Eds.), *Advances in pectin and pectinase research*. Dordrecht: Springer.

Thu, B., Gåserød, O., Paus, D., Mikkelsen, A., Skjåk-Bræk, G., Toffanin, R., Tittur, F., & Rizzo, R. (2000). Inhomogeneous alginate gel spheres: An assessment of the polymer gradients by synchrotron radiation-induced x-ray emission, magnetic resonance microimaging, and mathematical modeling. *Biopolymers, 53*(1), 60-71.

Tobil, M., Deh, C., Agbenorhevi, J., Sampson, G., & Kpodo, F. (2020). Effect of Okra Pectin on the sensory, physicochemical and microbial quality of yoghurt. *Food and Nutrition Sciences, 11*, 442-456.

Tolstoguzov, V. (2003). Some thermodynamic considerations in food formulation. *Food Hydrocolloids, 17*(1), 1-23.

Tolstoguzov, V. (2006). Texturising by phase separation. *Biotechnology Advances, 24*(6), 626-628.

Ventura, I., Jammal, J., & Bianco-Peled, H. (2013). Insights into the nanostructure of low-methoxyl pectin-calcium gels. *Carbohydrate Polymers, 97*(2), 650-658.

Voragen, A.G.J., Pilnik, W., Thibault, J.F., Axelos, M.A.V., & Renard, C.M.G.C. (1995). *Pectins, in: food polysaccharides and their applications*. (A.M. Stephen ed., Vol. 10, pp. 287-339). Dekker, New York (Reprinted from: Marcel Dekker, New York).

Walkenström, P., Kidman, S., Hermansson, A. M., Rasmussen, P. B., & Hoegh, L. (2003). Microstructure and rheological behaviour of alginate/pectin mixed gels. *Food Hydrocolloids, 17*(5), 593-603.

Wang, C., Liu, R., Wu, M., Zhai, Q., Sun, W., Jing, N., & Xie, F. (2021). Induced adsorption of pectin on copper-ion-modified galena surfaces: Flotation and adsorption mechanism. *Minerals Engineering, 173*, Article 107229.

Wang, C., Zhai, Q., Liu, R., Wu, M., Sun, W., Jing, N., & Xie, F. (2022). Using pectin to separate talc and molybdenite through the surface modification with Cu²⁺: Applications and mechanism. *International Journal of Mining Science and Technology*.

Wang, R., Liang, R., Dai, T., Chen, J., Shuai, X., & Liu, C. (2019). Pectin-based adsorbents for heavy metal ions: A review. *Trends in Food Science & Technology, 91*, 319-329.

Willats, W. G. T., Knox, J. P., & Mikkelsen, J. D. (2006). Pectin: new insights into an old polymer are starting to gel. *Trends in Food Science & Technology, 17*(3), 97-104.

Williams, M. A. K. (2020). Pectin gelation and its assembly into functional materials. In K. Vassilis (Ed.), *Pectin: technological and physiological properties*. Cham: Springer.

Wong, T. W., Colombo, G., & Sonvico, F. (2011). Pectin matrix as oral drug delivery vehicle for colon cancer treatment. *AAPS PharmSciTech, 12*(1), 201-214.

Wusigale, Liang, L., & Luo, Y (2020). Casein and pectin: Structures, interactions, and applications. *Trends in Food Science & Technology, 97*, 391-403.

Yapo, B. M., & Koffi, K. L. (2014). Extraction and characterization of highly gelling methoxy pectin from cashew apple pomace. *Foods, 3*(1), 1-12.

Yoo, S. H., Lee, B. H., Lee, H., Lee, S., Bae, I. Y., Lee, H. G., Fishman, M. L., Chau, H. K., Savary, B. J., & Hotchkiss Jr, A. T. (2012). Structural Characteristics of Pumpkin Pectin Extracted by Microwave Heating. *Journal of Food Science, 77*(11), C1169-C1173.

Zaitseva, O., Khudyakov, A., Sergushkina, M., Solomina, O., & Polezhaeva, T. (2020). Pectins as a universal medicine. *Fitterapia, 146*, Article 104676.

Zhou, M., Bi, J., Chen, J., Wang, R., & Richel, A. (2021). Impact of pectin characteristics on lipid digestion under simulated gastrointestinal conditions: Comparison of water-soluble pectins extracted from different sources. *Food Hydrocolloids, 112*, Article 106350.

Zykwinska, A., Boiffard, M. H., Kontkanen, H., Buchert, J., Thibault, J. F., & Bonnin, E. (2008). Extraction of green labeled pectins and pectic oligosaccharides from plant byproducts. *Journal of Agricultural and Food Chemistry, 56*(19), 8926-8935.

Zykwinska, A., Domagala, W., Czardybon, A., Pilawa, B., & Lapkowski, M. (2006). In-situ ESR spectroelectrochemical studies of overoxidation behaviour of poly(3,4-butylenedioxythiophene). *Electrochimica Acta, 51*(11), 2135-2144.

Zykwinska, A., Gaillard, C., Buleon, A., Pontoire, B., Garnier, C., Thibault, J. F., & Ralet, M.-C. (2007). Assessment of in vitro binding of isolated pectic domains to cellulose by adsorption isotherms, electron microscopy, and X-ray diffraction methods. *Biomacromolecules, 8*(1), 223-232.