# Microencapsulation of Anthocyanins--Critical Review of Techniques and Wall Materials
###### Abstract  
Anthocyanins are value-added food ingredients that have health-promoting impacts and biological functionalities. Nevertheless, there are technological barriers to their application in the food industry, mainly because of their poor stability and susceptibility to harsh environmental conditions, such as oxygen, temperature, pH, and light, which could profoundly influence the final food product's physicochemical properties. Microencapsulation technology is extensively investigated to enhance stability, bioaccessibility, and impart controlled release properties. There are many varieties of microencapsulation methods and diverse types of wall materials. However, choosing a proper approach involves considering the processing parameters, equipment availability, and application purposes. The present review thoroughly scrutinizes anthocyanins' chemical structure, principles, benefits, and drawbacks of different microencapsulation methods, including spray drying, freeze drying, electrospinning/electrospiraging, inclusion complexes, emulsification, liposomal systems, ionic gelation, and coacervation. Furthermore, wall materials applied in different techniques plus parameters that affect the powders' encapsulation efficiency and physicochemical properties are discussed. Future studies should focus on various processing parameters and the combination of different techniques and applications regarding microencapsulated anthocyanins in functional foods to assess their stability, efficiency, and commercialization potentials. annocyanins; microencapsulation methods; encapsulation efficiency; biopolymers; wall materials +
Footnote †: 2021: _Applied_  
also been detected. These sugars could also be acylated with various aliphatic/aromatic acids [6]. The number, type, and position of the attached sugar; the position and number of methoxyl and hydroxyl groups; the number, nature, and extent of organic acids linked to the sugar lead to the various structure of the anthocyanin molecules [7]. The incorporation of anthocyanins into food systems yet faces technological obstacles in the food industry, as these promising molecules are unstable and highly likely to degrade in the presence of light and oxygen, high temperatures between 100 and 121 \({}^{\circ}\)C, and slightly acidic to neutral conditions, resulting in poor bioavailability and color fading during processing and storage [5; 8; 9]. Microencapsulation is a satisfactory resolution regarding effectively protecting anthocyanins against adverse environmental conditions, and at the same time, providing physical stability, controlled release over time, enhanced bioaccessibility, and ease of handling and storage. In this process, a multicomponent structure is formed via entrapment of the solid, liquid, or gaseous substances as an active core material into a polymer as a wall or carrier material [10; 11; 12]. The products achieved using this process are different in size, ranging from 1 to 1000 \(\upmu\)m. The morphologies generated via microencapsulation are also diverse, including microspheres, microcapsules, and microparticles (Figure 2). In microspheres, the core material is dispersed in the matrix and on the surface, which is different from microcapsules. Microcapsules could either be mono- or polynuclear, where in the former, a single active compound is coated by a wall material, while the latter consists of two or more cores. The wall material with which the active ingredient is coated could be mono- or multilayered. Concerning microparticles, they might have an irregular shape [13]. Up to now, multifarious strategies have been successfully investigated for the microencapsulation of anthocyanins (Table 1), where the most widely employed methods are as follows:  
1. Physical methods, such as spray drying, lyophilization (freeze drying), and electro-spray/spinning. 2. Chemical methods, such as the formation of inclusion complexes. Figure 1: Chemical structures, colors, and sources of the most important anthocyanins [2]. 3.