Kappa-carrageenan improves the gelation and structures of soy protein isolate through the formation of hydrogen bonding and electrostatic interactions

Protein-polysaccharide interactions are crucial for developing plant-based food products. This study evaluated the impacts of κ-carrageenan (KC) on the gelling behaviors, viscoelastic properties, molecular interactions, and microstructures of the soy protein isolate (SPI)/KC complex gels. Our results showed that as the SPI/KC ratio increased from 100:0 to 95:5, the gelling process was prolonged. This facilitated the molecular interactions, aggregations, and crystallized structure reservation within the networks. The complex gels were therefore strengthened (γmax increased from 0% to 3%; Sg increased from 28.8 to 93.0 kPa·sn). However, excessive KC (SPI/KC = 90:10) would over-compact the gel (γmax = 8%; Sg = 165.5 kPa·sn). This could be ascribed to the evolutional SPI-KC interactions from the SPI/KC ratio of 100:0 to 95:5, and the predominant segregated SPI-KC interactions at 90:10. The microstructure observations further supported that KC induced complex coacervates formation at SPI/KC = 97:3 and 95:5 but caused phase separation at SPI/KC = 90:10. Through the deepened understanding of the SPI-KC interactions, this study serves as a theoretical support for the further industrial applications of the SPI/KC complexes in the plant-based food category.