# Anthocyanin Delivery Systems: A Critical Review of Recent Research Findings
## 1 Introduction  
Anthocyanins (ACNs) are an important class of over 700 polyphenolic, water-soluble natural pigments within the flavonoid family, and characterize various colors, including red, purple, and blue, in a wide range of vegetables, fruits, flowers, and seeds [1, 2]. ACNs have demonstrated significant bioactive attributes, and health-promoting benefits, such as antioxidant, anticarcinogenic, anti-inflammatory, cardioprotective, and anti-neurodeggenerative properties, as well as preventative effects against diabetes and ocular diseases, and improvement of vision health [3]. Furthermore, the ACNs isolated from various fruit berries have exhibited the potential to boost cognitive brain function and prevent age-related oxidative damage [4]. These natural pigments also exhibit good potential for various food-related applications. However, a major limitation regarding the use of ACNs for such applications is their degradation owing to sensitivity to various process-associated factors, such as temperature, light, pH, oxygen, co-pigmentation, enzymes, ascorbic acid, and sulfites [5]. The structure of ACNs generally comprises a single glucoside unit, although various ACNs contain multiple glucoside unit attachments in their structure (Figure 1), occurringas simple sugars, or oligosaccharidesacharide side chains, in a characteristic tricyclic (C6-C3-C6) skeleton pattern, and, therefore, can be termed anthocyanin glycosides [6]. The polar hydroxyl group [OH] present in ACNs facilitates the ACN molecules to form hydrogen bonds with water molecules [7]. The type of color imparted by an ACN, and its intensity is dictated by the number of OH and methoxyl (O-CH\({}_{3}\)) groups present in the ACN structure, whereby a greater number of OH groups characterize a bluish shade, while more O-CH3 groups impart reddish hues [8]. All higher plants have ACNs in their various tissues, and the most widespread, naturally occurring ACNs are based on six aglycones: cyanidin (50%), pelargonidin (12%), petunidin (7%), delphinidin (12%), peonidin (12%), and malvidin (7%), differing only in terms of B-ring substitution patterns (Figure 1) [9]. ACNs present in fruits, although highly sensitive to chemical and enzymatic degradation reactions, are highly reactive molecules, with significant chemoprotective activity against various diseases, such as diabetes, obesity, and some cancers [5]. This enhanced chemical reactivity can be attributed to the presence of the specific py  
Figure 1: Chemical structures of predominant ACNs pigments present in various plants; (**a**) Basic structure of an ACN; (**b**) Pelargonidin; (**c**) Cyanidin; (**d**) Delphinidin; (**e**) Peonidin; (**f**) Petunidin. in their structure [10]. Primary factors that affect the stability of ACNs include copignments, temperature, light, oxygen, pH, enzymes, metal ions, solvents, intramolecular, and intermolecular associations, other reactive compounds, as well as the type, and structure of the ACN pigment [11]. These factors, therefore, are key considerations in terms of applications involving ACNs in the food and pharmaceutical industries. ACNs are being utilized as natural, water-soluble, Codex Alimentarius-approved food colorants (E163), and dyes for a diverse range of food and beverage products [12; 13]. Encapsulated ACNs are also used as fortifications in cereal products (cookies, wafers, biscuits, and tortillas), juices, beverages, and milk products [14; 15]. ACNs encapsulated in gelatin/CH electrospray microparticles could be used in formulating functional liquid and nutraceutical foods [16]. Additionally, ACNs are regarded as nutraceutical ingredients of considerable therapeutic potential for the development of advanced nutraceuticals and functional foods [4; 17]. Furthermore, ACNs have also found applications in the cosmetics and pharmaceutical industries, for instance, for the development of health supplements [18; 19].