2.3.1. Microparticles

Higuera-Ciapara et al. [44] developed non-homogeneous-sized AST microcapsules with a diameter of 5–50 μm, using a chitosan matrix cross-linked with glutaraldehyde by the multiple emulsion/solvent evaporation method. The system stability was evaluated based on retained pigment quantity during microcapsule storage at 25, 35 and 45 ◦C, which was quantified weekly by HPLC. For any of the treatments, the results did not show a

marked decrease in AST concentration in the microcapsules, and AST was maintained in stable conditions, as evidenced by poor isomerization and pigment degradation.

Oil bodies (OB) are minute plant organelles similar to liposomes, with 0.5–2.0 μm diameter, consisting of an oil core surrounded by a phospholipid monolayer with a proteinaceous membrane, and these are used to deliver phytohormones and other hydrophobic compounds in plants. These structures, which have been isolated from rapeseeds, have been shown to constitute a novel type of microcapsule that is suitable for the extraction of hydrophobic organic compounds from aqueous environments [52]. Hydrophobic compounds like AST that are used in cosmetics have been loaded into these systems, to protect them from oxidation. Acevedo et al. [43] developed AST microcapsules (AST-M) with OB extracted from *Brassica napus* seeds with high microencapsulation efficiency (>99%) and used a response surface methodology to optimize the microencapsulation conditions. The AST-M were examined by optical microscopy, which evidenced morphological stability, autofluorescence, spherical structures and an AST presence in the core. Their larger mean diameter (3.4 ± 0.5 mm) compared to those containing OB alone (1.56 ± 0.06 mm) was likely due to the AST intercalation into microcapsule monolayer, as previously described by other authors. Stability studies showed high stability of microcapsules to aggregation and coalescence, as well as a double half-life in the presence of air and light exposure compared with free AST, thereby highlighting the protective role of OB against AST degradation. After 2 h of cell incubation (CRL1730 endothelial cell line), antioxidant assays demonstrated the higher antioxidant power of AST-M in comparison with free AST, which was dose- and time-dependent. The cell viability assay did not show any cell toxicity, and microencapsulated AST displayed higher oxidative stability than its free counterpart. The authors suggested that the use of OB as a new delivery system is promising for the cosmetic field because it joins once in contact with the skin, releasing the antioxidant safely, and offers a new and natural carrier to deliver stable AST.

Lin et al. [45] searched for the best conditions to prepare AST that is encapsulated in sodium alginate beads, varying the concentrations of calcium chloride solution, medium, sodium alginate solution as the encapsulation agent, and Tween 20 as a surfactant, and selecting the average yield weight, microencapsulation yield, the average size of beads and loading efficiency as the responses. It seemed that the higher the alginate concentration, the higher the average weight and size of the beads. Different conditions of three-week storage were tested for free AST, AST encapsulated in various formulations, and a commercial product with 10% AST, in terms of bioactive content. The percentage of AST amount retained after storage was higher (90%) for beads compared to the controls without encapsulation, which suggests that the matrix covering the molecule protected it from thermal degradation and oxygen attack.

AST microspheres were developed by Liu et al. [46] using the supercritical anti-solvent (SAS) process and poly (L-lactic acid) as the polymeric carrier. The authors believe that this alternative method has grea<sup>t</sup> potential for preparing encapsulation systems, thanks to its single-pass process and mild operating conditions, to prevent the degradation of AST and other sensitive molecules. SAS operating conditions were varied according to an orthogonal experimental design to elucidate encapsulation circumstances. Optimal conditions ensured an encapsulation efficiency of 91.5% and a mean particle size of 954.6 nm. Characterization assays proved the formation of uniform particles and the amorphous state of AST encapsulated in the matrix, while 6-month storage tests at 40 ◦C showed the enhancement of its stability.
