A new strategy for maintaining the thermal stability of phycocyanin under acidic conditions: pH-induced whey protein isolate-phycocyanin coprecipitation forms composite with chitosan

Phycocyanin is prone to degradation under acidic conditions and unstable at high temperatures, which is a key scientific issue limiting its application in food. Many methods have been used to maintain the stability of phycocyanin, but no excellent method has emerged. In order to achieve the application of phycocyanin in food (especially in beverages), this study innovatively utilized an effective method to combine phycocyanin with whey protein isolate by protein coprecipitation, and then coat it with chitosan to form composite particles. The composite particles not only maintained the blue color of phycocyanin, but also had colloidal stability. By simulating the conditions of pasteurization, high temperature short-term sterilization (HTST) and ultrahigh temperature transient sterilization (UHT), the color of the whey protein isolate (WPI) - phycocyanin (PC) chitosan (CS) composite solutions (pH = 3) changed slightly before and after heating, without significant apparent differences. The UV-vis spectra showed that the highest and lowest pigment retention rates of WPI-PCCS composite can reach 96.41% and 81.63%, respectively. The results of particle size, zeta-potential, SDS-PAGE, intrinsic fluorescence and FTIR analysis showed that phycocyanin was encapsulated in the helical structure of whey protein isolate, and chitosan was effectively attached to the surface of coprecipitated particles. Meanwhile, WPI-PC-CS composite also had excellent antioxidant capacity after heating. WPI-PC-CS composite had broken through the limitations of other materials in food applications and expanded the application of phycocyanin in acidic beverages and other food forms.