Enhancement of foamability parallel with foam stability of rice dreg protein by ions-induced treatment based on pH shifting: Interfacial properties and interaction mechanism

This work investigated the effect of pH shifting with NaOH/Ca(OH)2, as well as its combination with ion addition (Na+, K+, Ca2+, and Mg2+), on the regulating mechanism of foaming properties of rice dreg protein (RDP). The results showed that the foam ability of RDP, RDP subjected to pH shifting with NaOH and Ca(OH)2 (Na3 and Ca3), and RDP subjected to pH shifting combined with ion addition (Na3+KCl, Na3+CaCl2, and Na3+MgCl2) was 33%, 108%, 300%, 123%, 245%, and 177%, respectively. Notably, the Ca3 (73%) and Na3+CaCl2 (72%) samples also displayed exceptional foam stability among all samples. The SEM-EDS results revealed that Ca2+ gradually covered the bubble surface to form a smooth film within 30 min. The results of the interfacial properties showed that Ca2+ promoted the adsorption of protein molecules to the air-water interface at the fastest rate and induced the strongest interaction between protein molecules involved in forming the interface film. Besides, the particle size, zeta potential, FTIR, and amino acid composition analysis confirmed that Na+ bound to the amino groups of Asp and Phe, while Ca2+ primarily bound with RDP through interactions with the carboxyl oxygen and amino nitrogen of Gly, Tyr and Glu. Different ways of binding between protein molecules and ions resulted in differences in foam stability. This study can provide the theoretical basis for the ion-binding protein in interface-dominated food systems.