Effects of κ-carrageenan addition and chlorogenic acid covalent crosslinking on protein conformation and gelling properties of soy protein hydrogels

This paper reports the effects of κ-carrageenan (KC) additions (0.6% w/v) and covalent crosslinking by chlorogenic acid (CA) on the protein conformation and gelling properties of soybean protein isolate (SPI) hydrogels. Treatment with KC and CA changed the conformation of the SPI and improved the antioxidant capacity and gel properties, as confirmed by fluorescence spectroscopy, Fourier-transform infrared spectroscopy, antioxidant capacity analysis, and rheology measurements. The addition of CA (0.01 g/g-SPI) decreased the number of free amino groups, free sulfhydryl content, tryptophan fluorescence intensity, and surface hydrophobicity of SPI by 44.22%, 10.05%, 30.47%, and 44.61%, respectively, and increased the DPPH and ABTS radical scavenging activities by 30.29% and 40.69%, respectively. The addition of KC (0.6% w/v) enhanced the DPPH radical scavenging activities of the SPI-CA (0.002 and 0.01 g/g-SPI) conjugates by 11.29–16.50%, and improved the viscoelasticity, water immobilization, density, and thermal stability of the SPI–CA gels.