# Microencapsulation of Anthocyanins--Critical Review of Techniques and Wall Materials
## 2 Microencapsulation Techniques
### Physical Methods
#### 2.1.2 Freeze Drying
[51] revealed that the anthocyanin content and EE were 116.89 mg/100 g and 20.45%, respectively, with an anthocyanin-to-polymer wall material proportion of 2:1, followed by an increase to 151.68 mg/100 g and 21.11% in the ratio of 2:3. The EE, stability, and physical properties of the powder can be profoundly impacted by the composition and type of wall material. Maltodextrin is the most popular wall material that has been widely used in this technique. Mixing this wall material with other encapsulating agents has been examined to effectively preserve anthocyanins and produce better physical properties. To illustrate, anthocyanins from jaboticaba pomacewere microencapsulated with a different mixture of wall materials, namely maltodextrin (MD), MD-pectin (PEC), MD-soy protein isolate (SPI), and MD-pectin-SPI [52]. The most desirable physical properties in terms of the lowest hygroscopicity and solubility were recorded for maltodextrin-pectin-SPI, followed by maltodextrin-soy protein isolate and maltodextrin-pectin. This observation was connected to the interaction of different wall materials with anthocyanins during the process. On the one hand, amine and carbonyl groups of proteins form hydrogen bonds with the anthocyanins' hydrophilic region. On the other hand, the hydrophobic region of proteins interacts with the benzene ring of the anthocyanin. In water, microcapsules' solubility diminishes because the nonpolar parts of anthocyanins and proteins interact via van der Waals forces, reducing the nonpolar region exposed to water. Furthermore, the wall materials protect the adverse effect of UV on the total monomeric anthocyanins and antioxidant capacity, with the best performance being reported for MD-PEC-SPI (up to 99%). In the study of [PERSON] et al. [53], the combination of carboxymethyl starch (CMS) and xanthan (XG) gum resulted in an EE of over 96%. Still, there was no considerable impact when incorporating various xanthan gum ratios. It was concluded that if the wall material's viscosity surpassed the optimal value, the change in viscosity could not notably enhance the EE. The highest DPPH scavenging activity during incubation at 50 \({}^{\circ}\)C was reported for CMS/XG (30/1), followed by CMS/XG (60/1) and CMS/XG (90/1). Furthermore, the highest anthocyanin retention was observed for CMS/XG (150/1), which was 90.47% at 5 \({}^{\circ}\)C and 76.11% at 37 \({}^{\circ}\)C after 30 days. In the study of [PERSON] et al. [54], red aspberry anthocyanins were microencapsulated in SPI and gum Arabic. It was highlighted that using two wall materials was more effective than utilizing a single wall material in terms of the EE and stability. In this direction, blending 2.5% (w/v) of SPI and 2.5% (w/v) of gum Arabic led to the highest efficiency (98.87%) and thermal stability. Using a pure extract produced anthocyanin retentions of 26.81% and 17.32% at 37 \({}^{\circ}\)C after 30 and 60 days, respectively, whereas anthocyanins encapsulated in SPI-gum Arabic had 60.26% and 48.32% retentions after the same respective periods. In contrast, [PERSON] et al. [55] investigated the storage stability of anthocyanins from saffron petals that were microencapsulated using maltodextrin and gum Arabic conjugates. The outcome revealed no significant difference in the protective effect when using a single wall material and various compositions over 10 weeks at 35 \({}^{\circ}\)C.  
The DE of maltodextrin is of paramount importance in the stability and physical properties of pigments, and it has been investigated in the freeze-dried microencapsulation of anthocyanins. Maltodextrin with a lower DE might lead to the production of powder with lower water absorption due to the lower number of hydrophilic branches than maltodextrin with a higher DE [56]. Nevertheless, a higher DE might enhance the stability of anthocyanins because of the superior T\({}_{\text{g}}\)[6].