Complex coacervation of soy protein isolate-limited enzymatic hydrolysates and sodium alginate: Formation mechanism...

The complex coacervation of soybean protein isolate and polysaccharide has been widely applied for preparing biopolymer materials like microcapsule. In this study, hydrolytic soy protein isolate (HSPI) was prepared by mild hydrolysis of soy protein isolate (SPI) with fungal protease 400 (F400). The degree of hydrolysis (DH) for the enzymatic products was controlled at 1%-5%. Emulsification, oxidation resistance, and thermal stability were used to evaluate the performances of HSPI with different DH. The results showed that the HSPI with the hydrolysis degree of 2% had the optimal property. Subsequently, the complex polymer of HSPI/SA was prepared by the coalescence reaction of HSPI and sodium alginate (SA). The turbidity curves manifested the optimal complex coacervation occurred at the ratio of 7:1 (HSPI:SA). Fourier transform infrared spectroscopy (FTIR) presented that the reaction involved electrostatic interactions between -NH₃ ⁺ in HSPI and -COO^- in SA. Isothermal titration calorimetry experiments indicated that the complex coacervation reactions of HSPI and SA arose spontaneously. The microencapsulation by complex coacervation of HSPI and SA was further produced for embedding sweet orange oil. The thermogravimetric analysis (TGA) result revealed that the microencapsulation system of HSPI/SA had a better heat resistance than that using the SPI/SA complex polymer.