Fabrication of gallic acid-soy protein isolate conjugates to stabilize O/W emulsions for vitamin D3 delivery

To enhance the bioaccessibility of vitamin D3 in fortified food systems, hydrodynamic cavitation, ultrasonic cavitation, and an ascorbic acid/hydrogen peroxide system were employed to generate free radicals that mediated the formation of gallic acid-soy protein isolate (GA-SPI) conjugates. The resulting conjugates were used to stabilize emulsions. The emulsion properties and their effects on vitamin D3 delivery were investigated. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that covalent conjugation between GA and SPI was promoted by free radical generation in all three treatments. Compared with emulsions prepared with soy protein isolate alone, significant improvements were observed for emulsions stabilized by GA-SPI conjugates, including smaller particle size, higher absolute zeta potential, higher storage modulus, and improved storage stability and antioxidant capacity. These improvements were attributed to GA incorporation and the processing methods. More importantly, when used to encapsulate vitamin D3, bioaccessibility ranged from 53.36 ± 0.57% to 80.06 ± 0.12% for GA-SPI stabilized emulsions prepared by these methods, compared with the untreated group. These findings confirm that emulsion delivery performance can be improved by the three free radical-mediated treatments through promotion of polyphenol-protein conjugation.