# Algae Protein Creates Sustainable Alternatives for Various Food Matrices: From Function to Nutrition

Shaozong Wu, Paul Menut, Song Miao, Christelle Turchiuli

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Shaozong Wu, Paul Menut, Song Miao, Christelle Turchiuli. Algae Protein Creates Sustainable Alternatives for Various Food Matrices: From Function to Nutrition. Comprehensive Reviews in Food Science and Food Safety, 2025, 24 (5), pp.e70264. 10.1111/1541-4337.70264. hal-05235068

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COMPREHENSIVE REVIEW

OPEN ACCESS

# Algae Protein Creates Sustainable Alternatives for Various Food Matrices: From Function to Nutrition

Shaozong Wu¹,² | Paul Menut¹ | Song Miao³ | Christelle Turchiuli¹

¹Université Paris-Saclay, INRAE, AgroParisTech, UMR SayFood, Palaiseau, France | ²Guangdong Provincial Key Laboratory of Food Quality and Safety, National-Local Joint Engineering Research Center for Processing and Safety Control of Livestock and Poultry Products, College of Food Science, South China Agricultural University, Guangzhou, P. R. China | ³Teagasc Food Research Centre, Moorepark, Cork, Ireland

**Correspondence:** Christelle Turchiuli (christelle.turchiuli@agroparistech.fr)

**Received:** 24 February 2025

| **Revised:** 1 August 2025

| **Accepted:** 5 August 2025

**Funding:** Financial support was provided by the Marie Skłodowska-Curie Actions ALGAPOW Project 101067859.

**Keywords:** algae | algae protein food | alternative protein | protein functionalities | protein processing | protein profile

## Abstract

Protein deficiency and environmental deterioration are pressing and complex issues in traditional agriculture system. Algae, which can grow without the need of land and with minimal water, offer a rich source of protein. Recently, large-scale algae cultivation and advanced extraction techniques have been developed, positioning algae protein as a promising alternative to traditional animal proteins in various food categories. This review explores the global development of algae protein in the food industry, emphasizing its potential in association with animal protein or as a substitute for animal protein in foods. It highlights the importance of algae protein extraction and quality in food structuring and nutrition. Algae protein can be tailored to create a wide range of food products, though its properties are not fully understood and depend on cultivation conditions and extraction methods. Currently, the utilization of algae protein can be achieved through the use of entire biomass or of protein concentrates, which may contain a variety of proteins and non-protein components. Despite the challenges associated with non-purified algae protein, the field is advancing toward efficiently extracting protein from the algae matrix and incorporating it into new food matrices. This progress makes the application of algae protein in "blue foods" increasingly promising. However, like plant proteins, algae protein faces the dual challenges of sustainability and functionality.

## 1 | Introduction

The relentless pursuit of new food sources and high-yield agricultural production has been fundamental to the evolution of human civilization. Despite global hunger levels remaining stable in 2021 and 2022, the COVID-19 pandemic exacerbated food insecurity, affecting 9.2% of the population in 2022 (UNICEF 2023). This highlights the fragility of the current global food supply chain and underlines the importance of alternative foods to supplement the food source. Protein, an essential nutrient for human health, is crucial for bodily functions and development.

With the anticipated population growth, the global demand for protein is expected to surge, necessitating the expansion of food protein sources as well. Algae present a promising solution, being rich in protein and other micronutrients such as pigments, vitamins, and minerals. Compared to plant-based proteins, algae protein offers a higher yield upon extraction (Benelhadj et al. 2016; Teuling et al. 2019). Meanwhile, algal peptides also possess various functional benefits (Custódio et al. 2012), as well as a balanced profile of essential amino acids, making it a suitable alternative protein source in food. The growing awareness of health benefits has significantly boosted the European algae

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© 2025 The Author(s). Comprehensive Reviews in Food Science and Food Safety published by Wiley Periodicals LLC on behalf of Institute of Food Technologists.
<figure><img src="image_3.png" /><figcaption>**FIGURE 1** | Comparison of the characteristics of microalgae and macroalgae (European Parliament 2023).</figcaption></figure>

market, which grew by approximately 43% from 2016 to 2023 and is projected to reach 1240 million euros, compared to a global market value of 4810 million euros in 2023 (Mendes et al. 2022).

Regarding the sustainability of algae as a food source, algae production is environmentally friendly due to its lower land and water requirements compared to animal protein production or plant protein cultivation. As a source of essential nutrients, algae can be cultivated at a lower cost compared to traditional farming. Additionally, algae demonstrate greater adaptability in farming compared to crops and livestock (Fu et al. 2021). Over 70% of the Earth's surface is covered by water bodies such as oceans, seas, rivers, and lakes (Water Science School 2019). Algae could survive well in these vast water areas of Earth. Remarkably, algae can also be cultivated in deserts, utilizing less valuable land for food production. However, challenges such as exposure to excessive UV light and high salt concentrations due to intense evaporation must be addressed (Sikkema 2021). Furthermore, algae can be integrated into urban agriculture without occupying arable land, which could contribute to carbon neutrality by converting atmospheric CO₂ into carbohydrates, lipids, and other valuable bioproducts through photosynthesis (Sadvakasova et al. 2023). It is expected that the increased demand for algae in food production could help mitigate environmental greenhouse gas issues. Consequently, algae represent a sustainable protein source for humanity.

Microalgae are eukaryotic photosynthetic microorganisms, primarily unicellular plants, encompassing various types such as dinoflagellates, green algae (Chlorophyta or Chlorophyceae), golden algae (Chrysophyceae), and diatoms (Bacillariophyceae), each offering distinct benefits for humans. In contrast, macroalgae are multicellular plants, typically yielding higher outputs than terrestrial crops. Common macroalgae, such as seaweed, are rich in protein, minerals, and vitamins (Boukid et al. 2021; Packer et al. 2016) (Figure 1). Barba (2017) identified four major challenges for utilizing microalgae and seaweeds in food applications: defining molecules of interest, developing extraction techniques and processing methods, identifying the relationship between the algae matrix and yield, and optimizing algae extraction processes.

In recent years, the industrial use of algae has expanded significantly from animal feed to human food. Figure 2A illustrates the rapid development of algae protein in the food sector. From the 1960s to 2019, the algae industry evolved from initial discovery and scaling-up phases to becoming a recognized source for health products since 2013. Subsequently, algae experienced a substantial leap in development as a potential ingredient in plant-based food, such as in meat analogs. Although a number of research projects were conducted on algae between 2018 and 2024, it should be noted that those focusing on food applications are comparatively fewer, which suggests an important place for the study of algae for food purposes (Figure 2B). To foster the growth of the algae industry, global policies regarding algae food products have become more prevalent. Notably, algae species without a prior consumption record before 1997 require authorization, with food safety considerations in mind.

1. In EU, in 2022, 22 algae species were approved as novel food resources, but strict regulation of food safety issues, particularly contaminants and pathogens, remains essential (Su et al. 2023). In line with the Paris Agreement, the EU is leveraging the bioeconomy to reduce its carbon footprint, and European policies strongly support a sustainable food system to protect the environment and increase yields through alternative food sources. Thus, projects such as “Food and Natural Resources” have been funded under the Horizon Europe program (European Commission 2018). In 2020, European Commission has set a long-term goal of achieving carbon neutrality by 2050 (Araújo et al. 2021).

2. As for Asia, Asians have a long-standing tradition of algae consumption and are witnessing rapid growth in alternative food development from both marine sources and fermentation processes. Looking ahead, algae are expected to be consumed not only as a traditional dish but also as a novel protein source (Mendes et al. 2022). A significant policy introduced by the central government of China in 2023 emphasized the importance of diversifying the food supply system by developing microorganisms, edible fungi, and algae-based foods alongside traditional plant and animal sources (Grahame 2023).

3. In the United States, New York Mayor Eric Adams has committed to reducing the city's food-based emissions by 30% by 2030. The government is closely monitoring the safety of algae as a food source, where some are deemed Generally Recognized as Safe (GRAS) and some others are looking to be declared GRAS (Su et al. 2023).

Algae can function as an efficient bio-factory for producing protein. Following cultivation and harvesting, algae undergo extraction processes to utilize their protein content effectively. This process involves complex steps of cell disruption and protein enrichment by mechanical, chemical, or biological methods. Isolated algae protein holds significant potential for expanding its application in food. Innovative extraction methods, such as ultrasound-assisted extraction, pulsed electric fields, and microwave-assisted extraction, enhance protein extraction quality compared to traditional methods. These new techniques improve the yield and quality of bioactive peptides, which have applications in human nutrition, animal feed, and aquaculture (Bleakley and Hayes 2017). The quality and quantity of algae protein significantly impact the final product, which is also
<figure><img src="image_4.png" /><figcaption>**FIGURE 2** | Algal protein development in the food sector analyzed by MyLens.AI in a topic "The Rise of Algae Protein in Human Nutrition" (A). Published studies in all research fields dealing with "algae protein" between January 2018 and January 2024 in the Web of Sciences (VOS VIEWER software) (red: biology; blue: healthiness; green: biomass production; yellow: diet) (B).</figcaption></figure>

determined by the target consumers. Several factors potentially influence the quality of algae protein: 1. anti-nutritional factors like lectins; 2. cultivation conditions; 3. proximate biochemical composition; 4. type of algae species. Additionally, considerations such as protein content and amino acid profile, protein and essential amino acid digestibility, and biological performance evaluation of protein utilization are crucial (Bhatnagar et al. 2023).

To apply algae protein into food, it is necessary to clarify the functionalities of algae protein after extraction. The functionalities of algae protein encompass a wide range of properties, including solubility, emulsification, gelation, and foaming. These functionalities form the foundation for developing algae-based food products and depend on the extraction processes applied to the algae protein. Despite significant challenges in optimizing these functionalities, advancing algae applications in food requires an interdisciplinary approach that integrates science, technology, engineering, and product processing. Although health concerns related to algae protein are important, the potential benefits of incorporating algae into various food matrices should not be overlooked. The limited current application of algae in food means that many of these benefits have not been fully explored or clarified (Ahmad and Ashraf 2023).

The objective of this review article is to provide an updated overview of the use of algae proteins for applications in the food industry, while highlighting the relationship between protein functional properties and nutrition. It will therefore:

1. Compare algae protein to other sources regarding the composition and amino acid profile;

2. Highlight the effects of environment and processing conditions on the functionality of protein;

3. Show the barriers for algae protein to partially or totally replace animal protein in food.

After highlighting the potential of algae proteins in food, we will focus on extraction methods, both from a qualitative and quantitative point of view, for the production of algae proteins with ideal functional and nutritional properties for use in food.

## 2 | Literature Selection Criteria

The literature relating to this review article were collected comprehensively, especially the latest research about algae in food. The keywords searching the literatures were as follow: "algae," "algae protein," and "alternative protein." An amount of 135 literatures were selected from the searching, where are at least 70 studies about algae protein, 16 studies about plant protein, 26 studies about animal protein, and the rest studies about the background of alternative protein. The important results of the literatures were discussed to enlighten the potentials of algae protein in food from function to nutrition. The reliability and quality of literatures and citation were ensured during the review article writing.

## 3 | Protein and Amino Acid Profile of Algae

Algae protein is an ideal food source that meets both the quantity and quality requirements for human nutrition. It provides a rich
supply of protein, along with a comprehensive amino acid profile that includes all essential amino acids.

## 3.1 | Protein

The protein classes and types in algae are diverse and complex, similar to those found in leguminous seeds (Teuling et al. 2017). SDS-PAGE analysis reveals that the protein composition of *Tetraselmis* sp. includes molecular weights of 50, 40, 25, and 15 kDa, with a distinct band observed at 50 kDa, whereas the bands smaller than 50 kDa could be the enzymes (e.g., RuBisCo) of polypeptide structure (Schwenzfeier et al. 2011). The soluble protein isolates of *Nannochloropsis gaditana* and *Tetraselmis impellucida* are abundant in RuBisCo, comprising approximately 20%-40% of the total protein. In contrast, the protein isolate from *Arthrospira maxima* is predominantly composed of C-phycocyanin. Additionally, the protein isolates of *N. gaditana* and *T. impellucida* contain a higher proportion of multimeric proteins compared to *A. maxima*. Notably, high levels of monomeric proteins are found in these soluble protein isolates (Teuling et al. 2019). Generally, the protein content remains stable within the same algae strains. An important point to take into account for protein quantification is that compared to animal proteins, algae proteins contain a portion of non-protein nitrogen. Recent studies indicate that non-protein nitrogen contributes an average of 5.3% to the protein calculation (Sägesser et al. 2023).

## 3.2 | Amino Acids

Amino acids, particularly essential amino acids, are fundamental for human protein synthesis and food formulation (Le Roux 2019). According to the FAO dietary requirements for adults (WHO 2007), alternative protein sources must provide a balanced amino acid profile. Algae proteins offer a well-balanced profile of essential amino acids compared to certain plant, animal, and insect proteins (Table 1). For instance, the essential amino acid scores for *Chlorella* sp. and *Spirulina Bio* are 107.5 and 102.6, respectively (Mišurcová et al. 2014). For comparison, the amino acid scores of casein, minced beef, and soy protein are 99, 93, and 69, respectively (Friedman 1996). This indicates that their amino acid profiles are comparable to those of some animal proteins, such as milk protein (Fu et al. 2021). Regarding the distribution of amino acids within the algae matrix, non-essential amino acids are predominantly located in the internal regions of the algae (Safi, Charton, et al. 2014). The overall amino acid content of brown seaweed *Himanthalia elongata* (Linnaeus) S. F. Gray is reported to be 54.02 ± 0.46 g/kg dry matter, with particularly high levels of lysine and methionine (Garcia-Vaquero et al. 2017). Ideal amino acid profiles are characterized by high content and consistency. Two strains of *Galdieria sulphuraria* exhibit comparable amino acid compositions, demonstrating significant intraspecies biological conservation across different strains (Canelli et al. 2023). This high level of conservation is evident regardless of the trophic mode. Furthermore, the amino acid profiles of *G. sulphuraria* strains outperform those of some food-grade primary algae (e.g., *Arthrospira* and *Chlorella*) and plant proteins (e.g., soybean) (Abiusi et al. 2022; Canelli et al. 2023). Thus, the quality of algae protein is closely related to the species and processing strategies employed (Table 2).

# 4 | Functional Properties of Algae Proteins

The next generation of plant-based foods will likely face challenges related to quantity, diversity, cost, quality, and innovative processing. These challenges are heavily dependent on the structure-function relationship and nutritional profiles of proteins in product development (McClements and Grossmann 2023). The functional properties of proteins are determined by their structure and assembly state, which are influenced by environmental factors and processing techniques (Figure 3), also known as techno-functional properties (Buchmann et al. 2019; Waghmare et al. 2016). Gentle processing methods are preferred for protein extraction in food development to preserve protein functionality. Practically, harsh extraction procedures, whether physical or chemical, can significantly alter the hierarchical structures of algae proteins, thereby affecting their functional properties. For example, chemical methods that disrupt protein structures can enhance emulsification abilities. Both the initial protein production process and subsequent post-processing steps can significantly modify protein functionality. For instance, sonication facilitates the formation of protein aggregates through free sulfhydryl bonds and surface hydrophobic groups (Dabbour et al. 2024). To gain a comprehensive understanding of algae protein production and its impact on protein quality, Waghmare et al. (2016) analyzed *Chlorella pyrenoidosa* as a model algae. The effects of various factors, such as solvent type, ammonium sulfate concentration, solid load, pH, incubation time, slurry-to-butanol ratio, and enzymatic treatment, on protein yield were investigated. They also examined how these factors influence protein characteristics, including composition, dried mass color, water and oil holding capacity, foaming capacity and stability, and thermal properties (Waghmare et al. 2016). Subsequently, it is of great importance to elucidate the relationship between protein structure and processing methods.

## 4.1 | Solubility

### 4.1.1 | Mechanisms of Protein Solubility

Protein solubility is a crucial determinant of both the functionality and techno-functional properties of proteins (Schwenzfeier et al. 2011). Low protein solubility can adversely affect the functionality of proteins, leading to reduced performance in various applications. Grossmann and McClements (2022) provided a comprehensive analysis of how environmental conditions, such as temperature, pH, ionic strength, and solvents, affect protein solubility by modifying the protein's surface properties and structural conformation (Figure 3B). For example, elevated temperatures can alter protein mobility and cause structural denaturation, leading to increased protein aggregation.

### 4.1.2 | Comparative Analysis With Other Proteins

The aggregation of algae polypeptides is notably influenced by the pH of solution, as evidenced by Bernaerts et al. (2017), who observed increased aggregation at pH 6 when subjected to thermal treatment. This behavior underscores the significant role of solution conditions in determining protein aggregation. In particular, ionic strength and pH have profound effects on protein
<table><caption>TABLE 1 | Essential amino acids composition of some microalgae, macroalgae, animal, and insect food (DW%, on dry weight basis; %, on wet weight basis).</caption><thead><tr><th>Categories</th><th>Threonine</th><th>Valine</th><th>Methionine</th><th>Isoleucine</th><th>Leucine</th><th>Phenylalanine</th><th>Lysine</th><th>Histidine</th><th>Tryptophan</th><th>References</th></tr></thead><tbody><tr><td><strong>Animal</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Bovine milk. %</td><td>0.24</td><td>0.23</td><td>0.14</td><td>0.19</td><td>0.42</td><td>0.23</td><td>0.38</td><td>0.24</td><td>–</td><td>Landi et al. (2021)</td></tr><tr><td>Angus Beef, %</td><td>0.92</td><td>0.82</td><td>0.50</td><td>0.79</td><td>1.34</td><td>0.79</td><td>1.78</td><td>0.91</td><td>0.41</td><td>Alekseeva and Kolchina (2019)</td></tr><tr><td>Egg, %</td><td>0.613</td><td>0.7818</td><td>0.3943</td><td>0.6983</td><td>1.100</td><td>0.6798</td><td>0.923</td><td>0.2968</td><td>0.147</td><td>Attia et al. (2020)</td></tr><tr><td>Chicken breast, %</td><td>1.05</td><td>1.02</td><td>1.06</td><td>0.83</td><td>1.51</td><td>0.79</td><td>2.12</td><td>0.74</td><td>0.44</td><td>Dalle Zotte et al. (2020)</td></tr><tr><td><strong>Microalgae</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Spirulina (Arthrospira platensis), DW%</td><td>3.961</td><td>2.789</td><td>0.807</td><td>2.534</td><td>3.969</td><td>1.902</td><td>2.262</td><td>2.739</td><td>–</td><td>Raczyk et al. (2022)</td></tr><tr><td>Scenedesmus sp., DW%</td><td>1.208</td><td>1.499</td><td>0.519</td><td>1.04</td><td>2.124</td><td>1.403</td><td>1.717</td><td>0.524</td><td>–</td><td>Noreen et al. (2021)</td></tr><tr><td>Chlorella vulgaris, DW%</td><td>1.268</td><td>1.571</td><td>0.549</td><td>1.011</td><td>2.29</td><td>1.45</td><td>1.698</td><td>0.561</td><td>–</td><td></td></tr><tr><td>Chlorella sp., DW%</td><td>5.1</td><td>6.8</td><td>2.8</td><td>4.8</td><td>9.9</td><td>6.0</td><td>6.6</td><td>2.3</td><td>1.0</td><td>Pereira et al. (2019)</td></tr><tr><td>Tetraselmis sp. CTP4, DW%</td><td>1.27</td><td>1.55</td><td>0.61</td><td>1.12</td><td>2.28</td><td>1.44</td><td>1.70</td><td>0.04</td><td>0.37</td><td></td></tr><tr><td>Tetraselmis chui, DW%</td><td>4.1</td><td>4.9</td><td>2.5</td><td>3.5</td><td>7.5</td><td>4.8</td><td>5.7</td><td>1.6</td><td>2.4</td><td></td></tr><tr><td>Arthrospira sp., DW%</td><td>5.1</td><td>6.0</td><td>2.0</td><td>5.5</td><td>8.5</td><td>4.8</td><td>5.2</td><td>1.9</td><td>1.6</td><td></td></tr><tr><td><strong>Macroalgae</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Saccharina japonica (Kelp), DW%</td><td>–</td><td>6.5</td><td>0.6</td><td>1.9</td><td>2.4</td><td>0.9</td><td>1.3</td><td>0.4</td><td>8</td><td>Nie et al. (2023)</td></tr><tr><td>Himanthalia elongata (Sea Spaghetti), DW%</td><td>0.23</td><td>0.25</td><td>0.14</td><td>0.20</td><td>0.35</td><td>0.30</td><td>0.31</td><td>0.09</td><td>–</td><td>Mohammed et al. (2021)</td></tr><tr><td>Alaria esculenta (Irish wakame), DW%</td><td>0.50</td><td>0.53</td><td>0.13</td><td>0.39</td><td>0.74</td><td>0.51</td><td>0.57</td><td>0.13</td><td>–</td><td></td></tr><tr><td>Palmaria palmata (Dulse), DW%</td><td>0.84</td><td>0.98</td><td>0.20</td><td>0.62</td><td>1.16</td><td>0.73</td><td>1.19</td><td>0.20</td><td>–</td><td></td></tr></tbody></table>

(Continues)
<table><caption>TABLE 1 | (Continued)</caption><thead><tr><th>Categories</th><th>Threonine</th><th>Valine</th><th>Methionine</th><th>Isoleucine</th><th>Leucine</th><th>Phenylalanine</th><th>Lysine</th><th>Histidine</th><th>Tryptophan</th><th>References</th></tr></thead><tbody><tr><td><strong>Plant</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td><em>Porphyra umbilicalis</em> (Nori), DW%</td><td>1.75</td><td>1.70</td><td>0.29</td><td>1.06</td><td>2.20</td><td>1.25</td><td>1.63</td><td>0.47</td><td>–</td><td></td></tr><tr><td>Pea, DW% of protein</td><td>2.5</td><td>2.7</td><td>0.3</td><td>2.3</td><td>5.7</td><td>3.7</td><td>4.7</td><td>1.6</td><td>–</td><td>Gorissen et al. (2018)</td></tr><tr><td>Hemp, DW% of protein</td><td>1.3</td><td>1.3</td><td>1.0</td><td>1.0</td><td>2.6</td><td>1.8</td><td>1.4</td><td>1.1</td><td>–</td><td></td></tr><tr><td>Soy, DW% of protein</td><td>2.3</td><td>2.2</td><td>0.3</td><td>1.9</td><td>5.0</td><td>3.2</td><td>3.4</td><td>1.5</td><td>–</td><td></td></tr><tr><td>Chickpea, DW% of protein</td><td>3.0</td><td>4.6</td><td>1.1</td><td>4.8</td><td>8.5</td><td>5.3</td><td>7.0</td><td>3.2</td><td>–</td><td>Rachwa-Rosiak et al. (2015)</td></tr><tr><td><strong>Insect</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Bombay locust, DW%</td><td>1.21</td><td>2.65</td><td>0.38</td><td>1.48</td><td>2.91</td><td>0.94</td><td>1.71</td><td>0.76</td><td>0.23</td><td>Köhler et al. (2019)</td></tr><tr><td>Scarab beetle, DW%</td><td>1.07</td><td>1.87</td><td>0.45</td><td>1.28</td><td>2.12</td><td>0.92</td><td>1.55</td><td>0.73</td><td>0.47</td><td></td></tr><tr><td>House cricket, DW%</td><td>1.20</td><td>2.01</td><td>0.44</td><td>1.09</td><td>2.34</td><td>1.03</td><td>1.73</td><td>0.69</td><td>0.29</td><td></td></tr><tr><td>Mulberry silkworm, DW%</td><td>1.10</td><td>1.36</td><td>0.77</td><td>0.95</td><td>1.70</td><td>1.15</td><td>1.69</td><td>0.68</td><td>0.34</td><td></td></tr><tr><td>Lesser mealworm, DW%</td><td>2.41</td><td>3.80</td><td>0.88</td><td>3.10</td><td>4.16</td><td>2.63</td><td>3.76</td><td>2.04</td><td>0.69</td><td>Malla et al. (2022)</td></tr><tr><td>Yellow mealworm, DW%</td><td>1.94</td><td>3.30</td><td>0.60</td><td>2.63</td><td>3.68</td><td>1.75</td><td>2.45</td><td>1.41</td><td>0.55</td><td></td></tr><tr><td>Black soldier fly, DW%</td><td>1.65</td><td>2.70</td><td>0.66</td><td>2.23</td><td>2.98</td><td>1.67</td><td>2.16</td><td>1.14</td><td>0.62</td><td></td></tr></tbody></table>
<table><caption>TABLE 2 | Algae protein extraction methods: Conditions and effect on protein yield and quality for different algae.</caption><thead><tr><th>Extraction method</th><th>Parameters</th><th>Protein yield</th><th>Protein quality and functionality</th><th>Algae</th><th>References</th></tr></thead><tbody><tr><td>Physical method</td><td>Homogenization</td><td>5% protein concentrate, 50 MPa, and 100 MPa; cell disruption rate and energy consumption</td><td>Along with the pressure and passing times</td><td>Improve thermal gelation</td><td>Carullo et al. (2018), Geada et al. (2021), Shkolnikov et al. (2021)</td></tr><tr><td></td><td>Bead milling</td><td>pH 6.5, 0.6 kWh/kg DW; be aware of heating and energy consumption</td><td>50.4% (DW) in the extract</td><td>High surface activity; excellent gelation</td><td>Geada et al. (2021)</td></tr><tr><td></td><td>High shearing</td><td>20,000 rpm, 96 kJ/kg<sub>SUSP</sub>; high efficiency</td><td>25.8% (w/w) of total proteins</td><td>Improved recover yields of intracellular compounds, including pigments; partial fragmentation of the trichomes</td><td>Carullo et al. (2021), Geada et al. (2021)</td></tr><tr><td></td><td>Sonication</td><td>0%-100% power, 35-130 kHz; limited application scale, high energy consumption</td><td>25.3%-76.6%, dependent on pH; maximum 82.1%, with protease</td><td>High level of umami-taste free amino acids; 50% flavored; free radical reaction</td><td>Geada et al. (2021), Hildebrand et al. (2020)</td></tr><tr><td></td><td>Pulsed electric field</td><td>Electric field strength 7.5-30 kV/cm each 5 s at batch mode; 20 kV/cm for 2 µs at continuous mode; mild cell disruption; energy input not relating to protein release; not competitive with mechanical method</td><td>Max 13% in <i>Neochloris oleabundans</i> at batch mode; 2.5%-3.5% in C. <i>vulgaris</i> and 1.9%-2.5% in N. <i>oleabundans</i> by continuous flow mode</td><td>\</td><td>Carullo et al. (2018), Lam et al. (2017)</td></tr><tr><td></td><td>Micro-fluidization</td><td>0-120 MPa</td><td>12% at 120 MPa</td><td>Protein degraded; released intracellular protein; reduced molecular weight; increased 20% digestibility in vitro</td><td>Ke et al. (2023)</td></tr></tbody></table>

(Continues)
<table><caption>TABLE 2 | (Continued)</caption><thead><tr><th>Extraction method</th><th>Parameters</th><th>Protein yield</th><th>Protein quality and functionality</th><th>Algae</th><th>References</th></tr></thead><tbody><tr><td rowspan="3">Chemical method</td><td>pH adjustment</td><td>Alkalization</td><td>98% protein in pH 12; 71% protein in pH 7</td><td>lower functionalities than in pH7</td><td>C. vulgaris</td><td>Ursu et al. (2014)</td></tr><tr><td rowspan="2">Isoelectric precipitation</td><td rowspan="2">Protein solubilization at pH 11, protein precipitation at pH 4.2 (with the aid of high-speed homogenizer)</td><td>83.9 ± 1.7 wt% protein in protein concentrate; 91.3 ± 1.2 wt% protein in protein isolate</td><td>Increased solubility and foaming ability; resistant to thermal denaturation</td><td>Spirulina sp.</td><td>Pereira et al. (2018)</td></tr><tr><td>35.2%; effective extraction</td><td>Taurine (43% in Fucus vesiculosus) is a sulfonic acid but similar to amino acid; Aspartic acid (10.9%-12.1%) and glutamic acid (12.1%-12.3%) are the predominant amino acids in the other algae</td><td>Fucus vesiculosus, Alaria esculenta, Palmaria palmata, and Chondrus crispus. F. vesiculosus</td><td>O' Connor et al. (2020)</td></tr><tr><td>Osmotic shock</td><td>20 g algae suspended in 1 L ultrapure water at 4°C</td><td></td><td></td><td></td><td></td></tr><tr><td>Alcohol treatment</td><td>Methanol, solid to liquid ratio 20 g/mL; homogenization 120 MPa; washed with ethanol (~20 g/100 mL)</td><td>25.8%</td><td>Increased whiteness; higher level of protein denaturation; reduced water solubility; decreased alanine and proline; higher digestibility; increased oil holding capacity and water holding capacity; higher foaming stability; higher level of chewiness, hardness, and gumminess</td><td>C. pyrenoidosa</td><td>Yang et al. (2024)</td></tr></tbody></table>

(Continues)
<table><caption>TABLE 2 | (Continued)</caption><thead><tr><th>Extraction method</th><th>Parameters</th><th>Protein yield</th><th>Protein quality and functionality</th><th>Algae</th><th>References</th></tr></thead><tbody><tr><td rowspan="2">Biological method</td><td>Cellulase</td><td>M. pyrifera (74.6%) and C. chamissoi (36.1%)</td><td>Antioxidant activity (M. pyrifera 83 µmol/TE g, C. chamissoi 35 µmol/TE g); antihypertensive activity (M. pyrifera)</td><td>M. pyrifera and C. chamissoi</td><td>Vásquez et al. (2019)</td></tr><tr><td>Xylanase</td><td>54.9% (conversion factor 6.25)</td><td>Enhanced amino acid content</td><td>P. palmata</td><td>Bjarnadóttir et al. (2018)</td></tr></tbody></table>

structure and solubility. Like many plant-based proteins, the solubility of algae proteins is highly pH-dependent (Schwenzfeier et al. 2013; Waghmare et al. 2016). Algae proteins generally exhibit high solubility within the pH range of 6–11, with the lowest solubility occurring around pH 4. For example, when the pH of *Nannochloropsis oculata* protein was adjusted, the solubility plateaued between pH 5.5 and 8.5. At alkaline pH levels, the solubility of algal proteins averaged around 51%, whereas at pH levels lower than 5.5, solubility dropped below 9%. Therefore, pH levels of 7 and 10 are often considered optimal for maximizing protein solubility. Cavonius et al. (2015) optimized the pH shifting strategy for protein recovery, determining that precipitation at pH 3 while alkalization to pH 7 or pH 10 was optimal when balancing protein solubility, pellet sedimentation, and acid addition. *Arthrospira platensis* proteins displayed a U-shaped solubility curve, with the lowest solubility (6.2% w/w) at pH 3 and the highest (59.6% w/w) at pH 10, reflecting its isoelectric point (pI) (Benelhadj et al. 2016). Studies on *Chlorella protothecoides* found that water-soluble proteins had over 84% solubility across a broad pH range (2–12), with the minimum solubility observed at pH 2. Conversely, the water-insoluble protein fraction showed low solubility over the entire pH range, without a distinct pI, with a maximum solubility 26.9% ± 2.8% observed at pH 12 (Grossmann et al. 2019). Schwenzfeier et al. (2011) reported that *Tetraselmis* sp. protein isolates achieved 64% w/w protein content, with the isolates being colorless and independent of ion conditions, unlike plant proteins (Schwenzfeier et al. 2011). In summary, pH shifting is a potent method for modulating the solubility of algae proteins. For instance, *Kappaphycus alvarezii* protein concentrates showed pH and salt-dependent solubility, with the lowest nitrogen solubility (33.72% ± 1.23%) at pH 4, attributed to the destabilizing effect of the pI (Suresh Kumar et al. 2014). Additionally, *Chlorella sorokiniana* dry powder, when dispersed at an alkaline pH of 8 post-homogenization, exhibited enhanced protein solubility (Li et al. 2024).

## 4.2 | Emulsifying Ability

### 4.2.1 | Mechanisms of Protein Emulsifying Ability

The emulsifying properties of algal proteins are intrinsically linked to their structural characteristics. The extraction process can enhance these emulsification properties simultaneously. For instance, protein extracted from brown seaweed demonstrated a water-holding capacity of 10.27 ± 0.09 g H₂O/g and an oil-holding capacity of 8.1 ± 0.07 g oil/g (Garcia-Vaquero et al. 2017). Despite this, the algal proteins with clearly known structure, even after filtration, can complicate their interfacial behavior. Algae can stabilize Pickering emulsions by acting as solid particles within the emulsion (Ebert et al. 2019; Mishra et al. 2020; Teuling et al. 2019).

Interestingly, purified algal extracts have been shown to improve emulsifying ability, but crude algal extracts also perform well in stabilizing emulsions. For example, emulsions prepared with crude extracts (0.5 w/w%) had a mean droplet size (d43) of 5.0 ± 0.1 µm, whereas those made with purified algae protein at the same dry mass concentration had a larger droplet size of 10.6 ± 0.2 µm (Figure 3A–C) (Böcker et al. 2021). However, Pickering emulsions stabilized with insoluble algal proteins were
found to be unstable due to flocculation during storage (Dai et al. 2020a, 2020b).

### 4.2.2 | Comparative Analysis With Other Proteins

Soluble protein isolates from *Tetraselmis* sp. exhibited superior emulsifying performance and stability compared to whey protein isolate at pH 5, attributed to the co-absorption of polysaccharides. This high emulsifying capacity is also due to the elevated protein content and stability (Schwenzfeier et al. 2013). Long-term stability of algal protein isolates is crucial, with *C. sorokiniana* proteins maintaining a monomodal droplet size distribution ($d43 = 232 \pm 22$ nm) and stability over 7 days. In contrast, *Phaeodactylum tricornutum* proteins, despite higher protein content (3.7 wt%), showed less stability, with a droplet size of $d43 = 334 \pm 12$ nm, but better performance under storage or salt conditions. However, *C. sorokiniana* protein demonstrated superior stability compared to *P. tricornutum* across pH treatments (Ebert et al. 2019).

The solution characteristics of algal proteins during rehydration are closely linked to their emulsifying ability. For example, *A. platensis* protein isolate, with an oil absorption capacity of $252.7 \pm 9.9$ g, exhibited lower emulsifying ability ($44.1\% \pm 0.9\%$) at its pI, which increased when deviated from this pH (Benelhadj et al. 2016). *Haematococcus pluvialis* protein showed significant emulsification potential both at its native pH and when adjusted to neutral pH (Ba et al. 2016).

The protein structure affects emulsifying ability through its behavior at interfaces. At a protein concentration of 6 g/L, algae proteins exhibited emulsifying capabilities similar to, though slightly lower than, sodium caseinate, which is known for its high emulsification capacity due to its unfolded and dissociated structure (Ba et al. 2016). This suggests that improving the emulsifying ability of algal proteins might be achievable by disrupting and stretching their structures. This insight parallels findings in plant proteins, where gentle chemical or enzymatic modifications enhance surface activity by exposing hydrophobic groups (Wojciechowski 2022). Plant proteins typically have a high $\beta$-sheet and low $\alpha$-helix content (Le Roux 2019). Additionally, acid-hydrolyzed insoluble microalgae proteins from *C. protothecoides* were effective in stabilizing emulsions against salt changes, indicating that electrostatic forces are not the sole factor in flocculation. Emulsions prepared at extreme pH conditions (2–3 or 8–9) were more stable compared to those at the pI (Dai et al. 2020a). The polarity of proteins can shift from polar to nonpolar at the oil-water interface due to protein unfolding (McClements 2023). The emulsifying capacity of proteins from various photosynthetic unicellular organisms depends critically on the protein concentration that covers the droplet surface (Teuling et al. 2019). Dai et al. (2021) investigated the effectiveness of insoluble algal proteins and their hydrolysates in stabilizing oil-rich emulsions containing over 50% oil. The hydrolysis was conducted using 0.5 mol/L HCl at temperatures of 65°C or 85°C for 4 h. Compared to those hydrolyzed at 65°C, the hydrolysate obtained at 85°C, characterized by its gel-like structure, demonstrated a superior ability to emulsify and stabilize emulsions more concentrated in

fats (Dai et al. 2021). These findings underscore the need for a comprehensive database on the surface activity of algal proteins to enhance our understanding and application of these proteins in various emulsification processes.

## 4.3 | Foaming Ability

### 4.3.1 | Mechanisms of Protein Foaming Ability

The foaming properties of proteins are primarily due to their ability to migrate to the air-water interface, reducing surface tension and stabilizing the foam to prevent coagulation (Waghmare et al. 2016). Proteins in food can function as either foam-forming or foam-stabilizing agents. For example, the foaming capacity of egg white protein is attributed to the combined effects of lysozyme, ovomucin, and ovalbumin. Similarly, algal proteins, being a mixture of various proteins, may exhibit comparable foam formation mechanisms (Murray 2020).

Foam-stabilizing molecules can be categorized by their size, with proteins as larger molecules attaching to the foam interface (Figure 3F). The flexibility of these proteins affects the formation of the interfacial film. A strong film covering the interface enhances foam stability (Amagliani et al. 2021).

### 4.3.2 | Comparative Analysis With Other Proteins

High flexibility in algae proteins can potentially be achieved by disintegrating their structure. For instance, globular plant proteins require greater flexibility for effective interfacial absorption (Amagliani and Schmitt 2017). Compared to whey protein and egg white albumin, the foaming ability of soluble algae protein is superior within a pH range of 5–7. Protein adsorption increases at high ionic strength and decreases near the isoelectric pH (Schwenzfeier et al. 2013). Acid-hydrolyzed algae protein at 85°C enhances foam formation, achieving a half-life of 2–3 h at concentrations as low as 0.1% and producing the largest foam volume with the smallest bubble diameter. At 5% protein concentration, the foam’s half-life extends to 5 h (Dai, Shivananda et al. 2020). Residues remaining after protein extraction, such as polysaccharides, can also affect the solubility and gelation ability of algae proteins (Schwenzfeier et al. 2014). The foaming ability of algae protein is pH-dependent. For instance, *H. elongata* protein concentrate shows the lowest foaming ability at pH 2 ($6.98\% \pm 0.16\%$) and the highest at pH 10 ($71.52\% \pm 4.81\%$), with intermediate values at pH 6 ($64.44\% \pm 2.22\%$) and pH 8 ($55.56\% \pm 6.92\%$) (Garcia-Vaquero et al. 2017).

## 4.4 | Gelation Ability

### 4.4.1 | Mechanisms of Protein Gelation Ability

Gelation is a common feature in various foods, enhancing taste and mouthfeel. Examples of gelled foods include yogurt, emulsified sausage, pudding, jam, and soft cheese. Integrating algae into these gelled foods as a nutrient enhancer or creating novel gelled algae-based foods is meaningful. Gelation can be achieved through heat treatment, enzymatic action, or acidification. The
<figure><img src="image_5.png" /><figcaption>**FIGURE 3** | Functional properties of algal protein from extraction to solution and use in emulsification, gelation, and foaming: influence of process and conditions of use. Influence of extraction and purification on color (A); influence of pH on solubility (B); mechanism of emulsion stabilization, influence of algae protein concentration (C) and purity (D); algae protein gelation regulated by temperature, microstructure of gel network observed by scanning electron microscopy (E); foam stabilization by algae, interfacial behaviors of algae observed by confocal laser scanning microscopy (F). Source: (A) Adapted from Böcker et al. (2021). (B) Adapted from Böcker et al. (2021). (C) Adapted from Dai et al. (2020b) and Böcker et al. (2021). (D) Adapted from Böcker et al. (2021). (E) Adapted from Grossmann et al. (2019). (F) Adapted from Amagliani and Schmitt (2017) and Buchmann et al. (2019).</figcaption></figure>

protein gelation like whey is well-known, whereas the gelation of algal proteins is less explored. Food gel formation can be classified into physical methods (heat, pressure), chemical methods (acid, ions), and biological methods (microorganisms, enzymes). Algal proteins require unfolding to change their original structure. Amino acids like histidine, lysine, and arginine exhibit pH-dependent effects on protein gelation (Wang et al. 2020).

The formation of an algal protein network involves both non-covalent and covalent bonds, bridging proteins or proteins with other components. Dominant forces in gel structure formation include hydrophobic interactions, hydrogen bonds, and disulfide bridges formed by cysteine residues.

### 4.4.2 | Comparative Analysis With Other Proteins

Aggregates may embed into the gel matrix, contributing to the unique gelation behavior of algal proteins. For instance, *Spirulina* protein denatures at temperatures above 60°C, forming initial crosslinking interactions related to the degree of aggregation. Although intermolecular disulfide bonds are not essential for forming the gel structure, they can strengthen it. Compared

to other food proteins, the critical gelling concentration of *Spirulina* protein isolate is relatively low, which is around 1.5% wt (Chronakis 2001). Grossmann et al. (2019) demonstrated that algae protein extracted from *C. sorokiniana* could form a stable gel structure with as little as 9.9 g protein per 100 mL at 61°C (Figure 3E). The gelation of algae protein is also influenced by environmental conditions. The gel structure is adversely affected by intensified ionic conditions and pH deviations from the native value (Grossmann et al. 2019). A flexible application of gelation properties is in 3D printing technology, which can tailor nutritional food for people at different ages. Notably, high dry mass *Spirulina* slurry mixed with vegetable oil was found to be printable as a viscoelastic emulsion gel with a plastic-like response (Feng et al. 2023).

## 5 | Applications and Technological Barriers of Proteins

The traditional consumption of algae often involves direct incorporation into dishes or cuisines, such as using kelp in Asian cooking. However, broadening the methods of algae consumption is essential for advancing its application in the food industry. For
instance, recent innovations have incorporated algae into noodles to enhance their protein content (Rodríguez De Marco et al. 2014). The successful application of algae protein largely depends on advances in protein processing technology. Algal protein has the potential to substitute animal-based proteins in various major food categories, including meat, milk, and eggs (Table 3). In the context of plant-based meat alternatives, algae are typically used in powdered form and processed through high-moisture or low-moisture extrusion. Similarly, for milk analogs, a powder matrix is crucial for easy handling and storage but requires adapted formulation and good rehydration properties. However, powder form may not be as critical for egg alternatives, especially at market for customers.

In addition to liquid forms, algae products or derivatives are frequently used in powdered form (Su et al. 2023). Drying processes are employed to remove water from algae, reducing water activity and facilitating long-term storage. However, intensive drying methods can compromise the nutritional value of the algae. For example, sun drying led to the disintegration of antioxidant components like vitamin C (Khaled et al. 2024). In addition, the properties of the powdered matrix are influenced by the drying technique used. Spray drying is commonly employed for producing food powders due to its ability to provide consistent quality and support continuous production. Factors such as feed viscosity, droplet size, and drying temperature can affect the properties of the powder matrix and the bioactivity of the microalgae (Vilatte et al. 2023). Freeze drying can also be considered for algae powder production, but reports from some companies indicate that freeze-drying can reduce the level of biomolecules in the biomass by up to 50%. A promising alternative is electrostatic spray drying, allowing drying under lower air temperature (Jayaprakash et al. 2023).

## 5.1 | Meat Analog

Between 1961 and 2014, global average meat consumption increased more rapidly than the population growth, rising from 20 to 43 kg per person per year (Ritchie et al. 2017). Red meat has been associated with adverse health effects, including cardiovascular disease and cancer (Aykan 2015). In response to these concerns, there has been a surge in the development of plant-based meat analogs, driven by their potential benefits for the environment, animal welfare, and nutrition (Ryu et al. 2023).

Meat analogs from algae can generally be categorized into two types. The first category involves using algal protein as a primary ingredient in high-moisture extrusion processes to create fibrous meat substitutes (Figure 4). This method replaces animal proteins entirely with plant proteins or algae biomass. However, challenges in this approach include replicating the appearance and texture of traditional meat. For instance, red-colored algae can be used to mimic the color of meat because of its red color, which is similar to hemoglobin (Fu et al. 2021). Although high-moisture extrusion of *Spirulina* can produce a fibrous structure, it may result in a darker color, a stronger earthy flavor, and reduced elasticity and firmness (Grahl et al. 2018). Combining algae protein with plant proteins can help refine the texture of meat analogs. Research has shown that the microalgal cell wall and fat

can hinder the formation of a fibrous structure, with the cell wall impeding protein interactions. A 30% addition of microalgae at 60% moisture content has been found effective in high-moisture extrusion processes after optimization (Figure 4B) (Caporgno et al. 2020). Recent studies on high-moisture extrusion combining algae with pea protein have highlighted that microalgal proteins with smaller molecular weights, higher solubility, and fewer hydrophobic sidechains may be less effective for forming a fibrous structure, underscoring the importance of protein composition, properties, and the electrolyte environment (Figure 4A) (Sägesser et al. 2024). Additionally, replicating the fat content in meat analogs is crucial. Companies like Profilet are focusing on algae-based alternatives to fish, indicating a growing market and continued innovation in meat analogs.

The second category of meat analogs incorporates algae as an additive to traditional meat products (Žugčić et al. 2018). Algae can be included in various meat products, such as sausages, burgers, and patties (Figure 5) (de Medeiros et al. 2021; Marti-Quijal et al. 2019). Different algae formulations affect the composition and characteristics of the final product. For example, chicken roti with 5.82 g/100 g *Spirulina* has a higher fat content compared to a sample with 5.04 g/100 g soy, which was ascribed to the lipid in algae. Generally, substituting plant proteins with algae can reduce the hardness, elasticity, and chewiness of meat products (Marti-Quijal et al. 2019; Marti-Quijal et al. 2018; Parniakov et al. 2018). Additionally, whole algal biomass can serve as a natural salt replacer in meat products, offering a potential reduction in sodium content (Espinosa-Ramírez et al. 2023).

## 5.2 | Dairy Analog

Global milk consumption increased significantly from 2017, reaching 828 million tons, with 83% of this total attributed to bovine milk (Górska-Warsewicz et al. 2019). A notable advancement in the development of milk alternatives has been made by Sophie's Bionutrients, a Singaporean company that claims to have produced the world's first microalgae-based milk. Additionally, incorporating seaweed extract into milk has been reported to enhance its antioxidant properties, improve shelf life, and fortify both its nutritional profile and texture (Figure 6). Microalgae have also been integrated into fermented dairy products such as cheese and yogurt to offer additional health benefits (Figure 6C-E) (Beheshtipour et al. 2013; Hernández et al. 2022; O'Sullivan et al. 2014; Roohinejad et al. 2017). In the dairy industry, proteins are typically isolated from raw milk and tailored for specific functionalities. However, algae proteins require an initial extraction process (Figure 6A,B). To use algae, the formulation and design of milk analogs must carefully address emulsion stability and overall nutritional content.

The physical and functional stability of milk analogs against environmental factors involves complex considerations. Factors such as small particle size and the addition of thickening agents can enhance the physical stability of milk analogs. Extreme pH levels, temperature fluctuations, and excessive shearing or shaking can lead to flocculation. Common defects in milk analogs include gravitational separation, creaming, sedimentation, flocculation, and coalescence (McClements 2020). For high-demand products like infant formula, which require stringent food safety and
<table><caption>TABLE 3 | Algae as a protein replacer in meat product or dairy product (L*: lightness; a*: red/green value; b*: blue/yellow value in CIELAB color chart).</caption><thead><tr><th>Food</th><th>Algae species</th><th>Protein and amino acids</th><th>Food quality</th><th>References</th></tr></thead><tbody><tr><td>Meat</td><td>Sausage</td><td>Spirulina and Chlorella</td><td>Higher level of glutamic acid, aspartic acid, lysine, and leucine</td><td>Marti-Quijal et al. (2019)</td></tr><tr><td>Chicken breast formulation</td><td>Spirulina and Chlorella</td><td>Higher level of total amino acids and glutamic acid in Spirulina; higher level of essential amino acids; good alternative protein in meat</td><td>Higher pH than non-algae samples; lower a*; higher ash level; good water holding capacity >4.30 g/100 g; deteriorated texture</td><td>Marti-Quijal et al. (2019)</td></tr><tr><td>Patties</td><td>Spirulina and Chlorella</td><td>High in total amino acids and essential amino acids; good source of sulfur containing amino acids</td><td>Higher pH; lower L* and a*, higher b*; decreased hardness, lower elasticity; deteriorated cohesiveness, gumminess, and chewiness</td><td>Marti-Quijal et al. (2018)</td></tr><tr><td>Extruding meat analog</td><td>Auxenochlorella prototocoides and soy protein concentrate</td><td>Undisrupted microalgae cells limit intracellular protein; hinder fibrous protein cross-linking</td><td>Lower a* and b*; slightly higher pH; texture not affected; no obvious taste change</td><td>Žugčić et al. (2018)</td></tr><tr><td>Extruding meat analog</td><td>Spirulina and soy protein concentrate</td><td>Suitable for partial replacement of soy protein</td><td>Decreasing cutting strength; reduced harness; resemble to chicken</td><td>Caporgno et al. (2020)</td></tr><tr><td>Dairy</td><td>Yoghurt</td><td>Isochrysis galbana</td><td>Intensified chicken flavor; darker product; fibrous, elastic, firm and layered product with 30%-50% Spirulina; juicy and soft mouthfeel; affect springiness</td><td>Grahl et al. (2018)</td></tr><tr><td>Liquid milk</td><td>Ascophyllum nodosum</td><td>Higher protein content</td><td>Rich in DHA; innovative green tonality</td><td>Matos et al. (2021)</td></tr><tr><td>Cheese</td><td>Spirulina platensis</td><td>Protein-polyphenol interaction</td><td>Stable solution; DPPH and ferrous-ion-chelating activities; increased a* and b*, decreased L*; negative sensory, fishy taste less intense odor and taste</td><td>O'Sullivan et al. (2014)</td></tr><tr><td></td><td></td><td></td><td></td><td>Bosnea et al. (2021)</td></tr></tbody></table>
<figure><img src="image_6.png" /><figcaption>**FIGURE 4** | Meat analog by high moisture extrusion: Influence of formulation on physico-chemical properties and fibrillary structure for soy, pea, and algae protein extrudates (Sägesser et al. 2024) (A); soy protein and algae extrudate (Caporgno, et al. 2020) (B).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**FIGURE 5** | Meat replaced by algae: turkey breast formulation (Marti-Quijal et al. 2018) (A), fresh pork sausages (Marti-Quijal et al. 2019) (B), and beef patties (Žugčić et al. 2018) (C).</figcaption></figure>

nutritional standards, alternative proteins are being explored (Le Roux 2019). Le Roux et al. (2020) found that pea and faba proteins resulted in reduced emulsion stability compared to real milk, exhibiting flecking upon powder rehydration. In contrast, soluble fractions of algae proteins are recommended for developing alternative infant formulas. Fortunately, the remaining algae protein isolates are often rich in charged polysaccharides, which contribute to improved emulsion stability (Teuling et al. 2019). The structure of algae proteins also affects their emulsifying abilities, with disrupted proteins showing better emulsification properties compared to less soluble fractions (Dai et al. 2020a, 2020b). Algae proteins are typically dark green, but alkaline conditions can protect chlorophyll while acidic conditions can degrade it, depending on the desired color (Cavonius et al. 2015). Decolorization can also be achieved through acidification sediment, as demonstrated with *Tetraselmis* sp. at pH 3.5 (Schwenzfeier et al. 2011). The shelf life of milk analogs depends on the stability of the product during storage. Seaweed extracts have been shown to provide DPPH radical scavenging activity, enhancing emulsion oxidative stability (Figure 6C) (O'Sullivan et al. 2014). However, research on the shelf life of algae milk analogs

remains limited due to the nascent stage of alternative protein development.

Despite their unique nutritional profiles, algae-based milk analogs often require supplementation to match the critical nutrients found in traditional milk. Comparative studies show that bovine milk excels as a natural calcium carrier, a nutrient often deficient in dairy analogs (Tangyu et al. 2019). Therefore, plant-based milk alternatives should be fortified with calcium. Zhou et al. (2021) found that while calcium fortification is crucial, excessive levels can negatively impact vitamin D bioaccessibility, highlighting the need for careful nutrient formulation. Additionally, incorporating lactic acid bacteria into dairy analogs can reduce anti-nutrient factors (Erem and Kilic-Akyilmaz 2024).

In dairy products, the food matrix can be either liquid or solid. Semi-solid dairy products include yogurt, whereas solid dairy typically refers to powder-based foods. Gelation in real milk is driven by the cross-linking of casein micelles. The addition of *Nannochloropsis salina* can hinder this gelation process due to ruptured cells and insoluble debris. Enhancing the solubility
<figure><img src="image_8.png" /><figcaption>**FIGURE 6** | Algae protein extracted from biomass (A); Microalgae processed into microalgal protein isolates followed by emulsions (B); algae added into dairy milk (C), in yoghurt (D), in cheese (E). *Source:* (A) Adapted from Chen et al. (2019). (B) Adapted from Teuling et al. (2019). (C) Adapted from O'Sullivan et al. (2014). (D) Adapted from Matos et al. (2021). (E) Adapted from Bosnea et al. (2021).</figcaption></figure>

of algal debris can improve gel structure (Muñoz-Tebar et al. 2022). Replacing casein with algae or algae combined with plant proteins results in a different gelation process, often requiring thermal treatment. For instance, a 9.9 g/100 mL algae sample could form a gel structure when heated to 61°C. Small algae protein-rich particles formed by high shearing can improve gel structure when combined with soy protein isolate (Grossmann et al. 2019; Wang et al. 2023).

## 5.3 | Egg Analog

Alongside meat and milk analogs, egg analogs occupy a significant share of the alternative food market. The future of this market is promising, with expectations of high production volumes, targeted marketing, and clear regulations to drive growth. Consumers are increasingly choosing vegan eggs for their cholesterol-free and clean label benefits (Boukid and Gagaoua 2022). High-quality algae protein contributes to the appeal of vegan eggs. However, processing algae protein to effectively substitute real eggs presents some challenges. Besides the difficulty in achieving the desired color for egg analogs, identifying key volatile compounds in algae remains a significant hurdle (Urlass et al. 2023). Currently, egg analogs are primarily available in liquid form, sterilized by pasteurization, and requiring further cooking to form a gel-like structure. This liquid form must mimic the gelation process of real eggs, which is heat-induced and irreversible upon cooling. Real eggs contain ovotransferrin and ovalbumin, which exhibit two distinct gelation peaks at 66°C and 81°C (Liu et al. 2020). The critical point for protein denaturation and gelation at 66°C must be replicated in egg analogs. So far, mung bean protein has shown promise in mimicking this gelation process, a development accelerated by the protein platform of JUST EGG, which combines science lab and kitchen lab to select

protein sources. Additionally, plant-based emulsion gels can be used to create egg yolk alternatives (Li et al. 2024). Inspired by plant-based eggs, algae-protein eggs could be developed on the basis of their gelation abilities. Research by Zhou et al. (2022) explored the potential of RuBisCo proteins, finding that despite a gelation peak around 66°C, RuBisCo proteins exhibited a single denaturation thermal peak and produced a more fragile gel. RuBisCo proteins are found not only in higher plants but also in algae, indicating significant potential for using algae-derived proteins in egg analogs. But this requires experimental result to check the possibility of egg analog by RuBisCo proteins from algae.

## 6 | Quantitative and Qualitative Algae Protein Production

Before being utilized in the food industry, algal protein is extracted from both edible macroalgae and microalgae. Typically, algae protein is consumed in the form of algal biomass, which contains proteins that are not fully purified. Alternatively, algal protein can be isolated from the biomass, providing more controlled functionality. The extraction process involves careful selection between chemical and physical methods for concentrating algal protein (Pereira et al. 2018). The general protocols for obtaining algal protein include fractionation and purification techniques such as membrane ultrafiltration and chromatographic methods, often combined with ion-exchange and gel-permeation chromatography (Ejike et al. 2017). Among some algae (A. (Spirulina) maxima, N. gaditana, T. impellucida, and Scenedesmus dimorphus), these methods generally yield protein isolates with a concentration of 62%-77% w/w in dry mass, resulting in a protein yield of 3%-9% w/w by mild isolation, irrespective of the protein sources and extraction methods used.
Protein concentration processes depend significantly on protein solubility, which is influenced by pH and the solution environment. Efficient and rapid recovery of protein is crucial for novel applications in protein utilization (Teuling et al. 2017).

## 6.1 | Cultivation and Production of Algae Biomass

The species of algae significantly impact the yield of protein after cultivation. For instance, *Spirulina* spp., *Chlorella* spp., and *Dunaliella salina* are frequently utilized due to their high protein content (Boukid et al. 2021). Algae are valuable for food production because they offer high protein levels, rapid growth rates, and adaptability to various water sources (Deepika et al. 2022). The scale of algae cultivation plays a critical role in determining the yield and applicability of algae. Small-scale cultivation can substantially increase the cost of developing algae-based food products. Consequently, scaling up cultivation operations can be advantageous for cost control. Additionally, algae absorb carbon from air or water to produce protein biomass, contributing to sustainable and carbon-neutral food production (Ahmad and Ashraf 2023). After cultivation, algae can be dried using various methods, including freeze-drying, hot-air drying, convective drying, infrared drying, spray drying, and tray drying. Drying enhances the algae's storage stability, transportation efficiency, and suitability for processing within the food industry (de Farias Neves et al. 2019).

## 6.2 | Protein Extraction and Enrichment

Extraction is the process of isolating and concentrating algal proteins from biomass (Figure 6A). Advances such as thermal treatment and high-speed centrifugation have simplified and improved protein extraction methods (Wang et al. 2022). However, low protein recovery rates may result from complex and inefficient extraction processes during refinement. Therefore, a more sustainable and straightforward method for extracting components from algae cells is needed.

Recovering soluble proteins from microalgae remains challenging due to the need to balance algal biomass quality with energy consumption. The efficiency of protein extraction is influenced by factors such as biomass concentration, physicochemical conditions during cell disruption, and subsequent processing steps, including bead milling, centrifugation, and microfiltration. Optimizing these processes can reduce the cost of microalgal protein extraction and purification to approximately €0.35/g of protein (Liu et al. 2021). Minimal processing methods, such as cell disruption followed by centrifugation and lyophilization, have also been reported to be effective for extracting water-soluble proteins (Grossmann et al. 2018).

Algae protein extraction can be achieved through physical, chemical, or biological methods (Table 2). The choice of method depends on the specific characteristics of the algae and the conditions used. Mechanical methods are particularly crucial for enhancing protein yield. For example, the effectiveness of various extraction techniques is ranked as follows: high-pressure cell disruption > chemical treatment > ultrasonication > manual grinding. Algae with more delicate cell structures are more

easily disrupted, with the following order of susceptibility: *H. pluvialis* < *N. oculata* < *Chlorella vulgaris* < *Porphyridium cruentum* ≤ *A. platensis* (Safi, Ursu, et al. 2014).

### 6.2.1 | Physical Methods

Physical methods are commonly employed to disrupt the protective structures of plant cells, including algal cell membranes, which inhibit protein release during extraction. Among these methods, homogenization has been shown to be more effective than enzymatic treatments for disrupting algal cells and enhancing protein extraction. However, the efficiency of protein recovery can be influenced by the type of filtration membrane used. Interestingly, large cut-off membrane (1000 KDa) had more severe fouling compared to smaller pore membrane (300 KDa), which resulted from the readily blocking of the large pores by polysaccharides (Safi et al. 2017). For instance, algae concentration in inlet feed, such as for *Nannochloropsis* sp., can reach up to 25% (w/w). Interestingly, the effectiveness of homogenization is more dependent on the pressure applied rather than on the feed concentration (Yap et al. 2015). Microfluidization is another technique that generates high energy by fluids collision in a high speed, which breaks particles down to micro- and nanoscale sizes. This method improves digestion of algae by breaking down cell walls, with pressures of 120 MPa resulting in 98% cell breakage and a 12% protein extraction rate. Furthermore, this process yields proteins with smaller molecular weights (Ke et al. 2023). The extraction process significantly affects the surface activity of crude *A. platensis* powder, although pigments often remain in the biomass post-extraction. Pulsed electric fields can mitigate negative impacts on the techno-functional properties of protein isolates (Buchmann et al. 2019). For optimal solubility and functionality, membrane filtration is recommended over sedimentation (Bleakley and Hayes 2017). Bead milling is another effective method for cell disruption, particularly for robust algae species like *N. oculata* and *P. cruentum*. High-pressure effects are analyzed using residence time distribution modeling to assess and optimize operating parameters, including stress intensities and stress numbers (Montalescot et al. 2015). Additionally, steam explosion is a cost-effective method for achieving complete cell disruption, which reduces overall extraction costs (Lorente et al. 2017).

### 6.2.2 | Chemical Method

Chemical methods play a crucial role in modifying the protein structure during extraction to enhance concentration. One widely adopted approach is pH shifting on the basis of the pI of the algal protein. This method often involves acid extraction followed by alkaline extraction, which can achieve a combined recovery efficiency of up to 59%, outperforming the 57% recovery obtained through a combination of alkalization and ultrasound treatment. Alkalization is a critical component of effective combined extraction strategies (Kadam et al. 2017). In another study, algae protein was first solubilized under alkaline conditions (pH = 11) and then precipitated by acidification (pH = 4.2), reaching the pI with the aid of homogenization. This method resulted in protein concentrates and isolates with purity levels of 83.9% ± 1.7% w/w
and 91.3% ± 1.2% w/w, respectively (Pereira et al. 2018). Bertsch et al. (2023) demonstrated that hydrochloric acid could effectively precipitate soluble algae protein. Sodium hydroxide is particularly effective in penetrating the cellulose microcrystalline structure and dissolving hemicelluloses protected by cellulose-rich cell walls, as observed in species like *C. vulgaris* and *N. oculata* (Safi, Charton, et al. 2014). Temperature also influences extraction efficiency; for instance, solubilizing *Nannochloropsis* biomass at 60°C and pH 11, followed by recovery at pH 3.2, can yield protein levels ranging from 40.5% to 56.9%, depending on the degree of biomass defatting (Gerde et al. 2013).

### 6.2.3 | Biological Method

Biological methods rely on enzymatic activity to facilitate the extraction of protein from algae. Enzymes play a crucial role in degrading the algal cell wall, thereby releasing protein components for further processing. Research indicates that enzyme-assisted disruption of the algae cell wall, often combined with other extraction techniques, enhances protein recovery. For example, after optimizing enzymatic treatment and incorporating three-phase partitioning, protein concentration achieved 78.1% w/w (Waghmare et al. 2016). Additionally, specific enzymes, such as xylanase, can significantly improve the yield and amino acid profile of algal proteins. For instance, xylanase treatment increased the extraction yield of protein from red seaweed (*Palmaria palmata*) to 80% after enzymatic pre-treatment (Bjarnadóttir et al. 2018). Cellulase could effectively degrade fibrillar skeleton whose matrix is of sulfated galactans, which reached a 36.1% protein yield in *Chondracanthus chamissoi* (Vásquez et al. 2019).

### 6.2.4 | Integrated Methods

Single-method approaches often fall short in effectively releasing protein from algal cells. Consequently, integrating multiple methods can significantly enhance protein extraction efficiency. For instance, combining alkaline treatment with mechanical methods can produce a synergistic effect, as demonstrated by Safi (2013). The integration of mechanical treatment and pH shifting has been shown to increase the yield of water-soluble biomolecules in *H. pluvialis* (Ba et al. 2016). High-pressure homogenization, in particular, has proven highly effective, releasing approximately 49% of proteins compared to 35% achieved through enzyme treatment alone. Additionally, integrating filtration with enzymatic processing has been found to enhance protein recovery, achieving a protein concentration of 24.8% (Safi et al. 2017). A multi-step approach can also significantly improve protein quality. For example, the protein quality of *Tetraselmis* spp. was greatly enhanced through a series of processes, including bead milling, centrifugation, ion exchange chromatography, and decolorization, resulting in a protein level of 64% w/w in soluble isolates (Schwenzfeier et al. 2011). Overall, combined methodologies, even within the same category, tend to yield higher protein extraction levels. Chemical and biological methods often soften the algal structure, whereas intensive physical methods further maximize protein extraction from algal cells.

## 6.3 | Protein Degradation and Bioactivities

The degradation of algae protein can be achieved through physical, chemical, or biological methods, each altering the protein's structure. This degradation can be a prerequisite for protein digestion and amino acid absorption. The effectiveness of algae protein digestion is closely related to the extent of its structural denaturation and degradation. Additionally, the bioactivity of algae protein is influenced by its degraded state. The bioactivities of peptides include anti-inflammatory, antioxidant, antidiabetic, antiobesity, and so forth. To evaluate the bioactivity of algae protein, several methods can be employed. In vitro methods: These include simulated gastrointestinal digestion, artificial membranes, Caco-2 cell cultures, and isolated or reconstituted cell membranes. Ex vivo methods: These involve lab-scale gastrointestinal organs. In situ methods: These use animal intestinal perfusion. In vivo methods: These include studies conducted in animals or humans. Each of these approaches provides insights into the bioactivity and functional potential of algae protein in different biological contexts (Carbonell-Capella et al. 2014).

### 6.3.1 | Digestion

Digestion involves the physical and biochemical breakdown of algae protein, which is essential for its subsequent absorption in the human body. Key organs involved in the degradation of algae protein include the mouth, stomach, and intestine. Initially, the algae food matrix is broken down by chewing in the mouth. This is followed by degradation by pepsin and pepsinogens in the stomach, and by pancreatin in the small intestine (Cian et al. 2015; Wells et al. 2017). To assess the extent of protein digestion, the degree of protein hydrolysis and amino acid bioaccessibility are evaluated (Le Roux 2019). A novel industry-scale microfluidization technique has been utilized, resulting in a 20% improvement in in vitro digestibility (Ke et al. 2023). Algae protein generally exhibits high digestibility, and novel methods can further enhance this process. For instance, the protein from the microalgae *Spirulina platensis* has been found to be digested at rates as high as 87.5%-97.8% (Ahmad and Ashraf 2023; Yucetepe et al. 2018).

The digestion of algae protein is typically compared to that of animal proteins to assess its potential as an alternative protein source. Algae protein generally has a weaker digestion ability compared to animal protein, such as casein (Wells et al. 2017). Despite this, microalgae-derived peptides with antihypertensive and antioxidant properties have been produced, which are closely related to peptide extraction methods. For algae protein to become a viable commercial alternative, large-scale microalgae cultivation, effective peptide release within food products, and evidence of health benefits through digestion are necessary (Ejike et al. 2017). Algae-derived peptides could offer various health benefits, including antioxidative, antihypertensive, immunomodulatory, anticancer, hepatoprotective, and anticoagulant properties. The potential health benefits of algae peptides have garnered significant research interest. However, most verification studies are still in the laboratory phase, and further research is needed to confirm these benefits on a larger scale (Caporgno and Mathys 2018).
## 6.3.2 | Bioavailability

The bioavailability of proteins is determined by the digestion and absorption of nutrients in the human body. In Becker's (2007) study, the protein efficiency ratio, biological value, net protein utilization, and digestibility of plant proteins were compared to those of animal proteins. Algae protein demonstrated a slightly lower degree of protein digestion compared to casein and egg protein (Becker 2007). In addition, protein bioavailability could be assessed by the protein digestibility corrected amino acid score (PDCAAS) (Jareonsin et al. 2024). The PDCAAS of algae is generally lower than the reference (Shabaka and Moawad 2021). Comparatively, the animal protein like milk, egg, beef, and fish had a higher PDCAAS values (0.92–1.00) than algae protein, which had a wide range of PDCAAS (0.29–0.84) (El Obeid et al. 2025). As for the algae species of low PDCAAS, it is suggested to combine these algae with other plant-based or animal-based protein to improve the overall protein digestion in food. In addition, some techniques could be developed to break down the cell wall or protein structure of algae. The bioavailability of algae protein also depends on cultivation conditions. Under mixotrophic conditions, the protein bioaccessibility of *G. sulphuraria* (SAG 108.79) and *G. sulphuraria* (ACUF 064) was 55.3% ± 1.8% and 16.0% ± 1.5%, respectively; in autotrophic conditions, it was 69.3% ± 2.8% and 12.1% ± 1.0%, respectively (Canelli et al. 2023).

## 6.3.3 | Bioactivity

The bioactive compounds in algae are not only proteins; other components such as phenolic compounds also play a significant role (Custódio et al. 2012). Moreover, the bioactivity of algae protein is primarily linked to degraded peptides (Fu et al. 2021; Le Roux 2019). Despite issues related to bitterness, bioavailability, and stability in different environments (Chakrabarti et al. 2018), algae remain a crucial nutritional supplement with numerous health benefits. Extracting protein from biomass can improve its bioaccessibility (Silva et al. 2025). Additionally, bioactive peptides can be recovered from algae protein waste (Sheih et al. 2009). *Spirulina*, for example, has significant applications in peptide products, offering functional activities such as ACE inhibition, antihypertensive effects, DPP-IV inhibition, and antimicrobial properties (Villaró et al. 2023). To obtain high-purity bioactive peptides, lipids and colorants are removed before hydrolysis. Peptides smaller than 3 KDa can then be concentrated by filtration, enhancing their bioactivity. Bread, a commonly consumed cereal-based product, is an ideal matrix for encapsulating bioactive compounds. Similarly, the bioactivity of flour-based foods is enhanced in some Asian dishes (Prabhasankar et al. 2009). Microalgae from different phyla exhibit antioxidant, metal-chelating, and acetylcholinesterase-inhibiting activities (Custódio et al. 2012). Polyphenols, released from disrupted algae cells, enhance antioxidant capabilities, with concentrations increasing alongside algae biomass. Notably, peptides degraded from proteins also possess antioxidant properties (Ejike et al. 2017; Lafarga et al. 2019). For instance, pasta enriched with *Spirulina* exhibits higher antioxidant activity (Rodríguez De Marco et al. 2014). The chelation of Fe²⁺ and Cu²⁺ is influenced by the concentration of algae extracts and species, with a 1 mg/mL concentration

achieving a minimum 73% chelating ability. Among various algae species, *N. oculata* demonstrates the best chelating ability (Custódio et al. 2012). Natural peptides from *Tetraselmis suecica* exhibit antibacterial activity without enzymatic effects (Guzmán et al. 2019). Additionally, the antihypertensive activity of algae peptides has proven effective, varying according to algae species and peptide types (Jiang et al. 2021).

# 7 | Conclusions and Future Perspectives

Algae represent a sustainable and promising food source due to their production efficiency, functional properties, and nutritional benefits. Unlike traditional agriculture, algae cultivation requires minimal land and has a high capacity for carbon dioxide adsorption, making it an environmentally friendly alternative. Microalgae, in particular, grow rapidly and can survive in extreme environments, making algae farming feasible even in outer space. Consequently, microalgae are promising for interstellar agriculture, serving as a food source for astronauts. The unique functionalities of algae protein form the foundation for its application in food development, offering distinct advantages over plant proteins. Algal protein can be utilized in mixing with animal protein or other plant protein, which has demonstrated unexpectedly superior functionality compared to many isolated proteins. This insight encourages food producers to consider two primary approaches for incorporating algae into food products: using the whole protein biomass or isolated proteins. Ultimately, leveraging the potential of algae protein could enhance the nutritional value of various foods and contribute to more sustainable food production practices.

## 7.1 | Cultivation and Production

The cultivation of algae for food purposes is advancing, requiring stringent hygienic conditions. Waste products from algae food processing can be repurposed for biofertilizers, biofuels, or bioplastics. Algae cultivation can be scaled up using unexploited areas such as deserts.

## 7.2 | Protein Extraction

Extreme chemical treatments may disrupt the original structure of algae proteins. However, mechanical methods should also be considered to enhance protein extraction. Clarifying the origins and methods of algae protein extraction is crucial, as understanding the relationship between extraction techniques and protein structure is necessary for optimizing the functionality of algae protein. High-protein biomass or isolated protein products are essential for large-scale application in the food industry. Future protein extraction efforts should focus on preserving protein functionality rather than solely on extraction efficiency.

## 7.3 | Protein Functionality

Enhancing protein functionality can expand the applications of algae. Solubility and emulsification are key functionalities, often prioritized over others. The functional properties of protein iso-
lates differ from those of whole biomass proteins. Isolated algae
proteins offer stable functionalities, whereas biomass proteins
provide a broader range of functional benefits. The functionality
of algae protein is heavily influenced by extraction methods and
environmental conditions.

7.4 | Algae-Based Food

The development of algae-based foods is in its early stages,
with algae protein primarily used in meat substitutes. Increasing
research is being conducted on aquaculture feed and pet food,
where techniques from plant-based foods can be adapted. How-
ever, developing algae foods involves addressing complex issues of
color, flavor, and taste. Currently, filtration and isolation of algae
proteins appear to be feasible solutions. Beverages fortified with
hydrophilic amino acids demonstrate enhanced nutritional value.

7.5 | Food Safety

Food authorities in various countries ensure the safety of algae as a food source. Special attention must be given to the cultivation environment, particularly when algae are grown in open spaces like ponds. If chemical extraction methods are used, it is crucial to manage salt intake or employ filtration techniques to reduce salt levels in the final product.

Author Contributions

Shaozong Wu wrote the manuscript. Shaozong Wu and Christelle Turchi-
uli collected and reviewed the literature while acting on the acquisition of
funding. Christelle Turchiuli, Paul Menut, and Song Miao contributed to
the analysis of the documents used and to the revision of the manuscript.
All co-authors read and approved the final manuscript.

Acknowledgments

It is appreciated that this research was financially supported by Marie
Skłodowska-Curie Actions (ALGAPOW Project 101067859).

Conflicts of Interest

The authors declare no conflicts of interest.

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