Complex coacervation of soy protein with chitosan: Constructing antioxidant microcapsule for algal oil delivery

- Soy protein(SP)/chitosan(CS) coacervation was driven by both entropy and enthalpy.
- SP/CS coacervates had a viscoelastic solid behavior with gel-like microstructures.
- SP/CS coacervated microcapsules had the advantage of higher encapsulation efficiency.
- SP/CS coacervates showed improved stability against algal oil oxidation.

Complex coacervation of soy protein isolate (SPI) with chitosan (CS) and the microencapsulation of algal oil using the SPI-CS coacervate were investigated. The ζ-potential and coacervate yield data showed that the optimal complexation pH and CS/SPI ratio were 6.0 and 0.125 g g−1, respectively. Isothermal titration calorimetry further confirmed that per molecule of SPI was saturated with 0.104 molecules of CS at pH 6.0, suggesting this binding was high affinity (Ka = 4.16 × 105 ± 0.09 × 105 M−1) and driven by both entropy and enthalpy. The rheological and microstructure measurement indicated that the SPI-CS coacervates had a viscoelastic solid behavior (G′ > G″) with highly interconnected gel-like network structures. The algal oil microcapsule fabricated by the SPI-CS coacervate showed advanced encapsulation efficiency and improved oxidative stability compared to the one encapsulated by SPI alone. The transglutaminase cross-linking could further improved the oxidative stability of SPI-CS microcapsule which proved by the reduced lipid hydroperoxides and volatile hexanal. This improvement was believed to be attributed to the antioxidant properties of CS as well as the increase of protection against oxidation by providing an oxygen barrier after complex coacervation and cross-linking.