Effect of glycosylation on soy protein isolate–sodium carboxymethyl cellulose conjugates heat-induced gels and their applications as carriers of riboflavin

The objective of this study was to improve the rheological properties and riboflavin delivery ability of soy protein isolate (SPI) gels by incorporating sodium carboxymethyl cellulose (CMC) through glycosylation. The investigation focused on the structural and gel properties of SPI–CMC conjugates at different Maillard reaction times (30, 60, 90, 120, and 150 min). The results showed that the degree of grafting initially increased and then decreased as the Maillard reaction times increased, reaching its peak at 90 min (25.52%). The changes in the structure and conformation of the SPI–CMC conjugates were verified by Fourier transform infrared spectroscopy and surface hydrophobicity. An appropriate Maillard reaction reduced the content of highly ordered α-helix and β-sheet while increasing the content of disordered random coil and β-turn. This secondary structural change led to protein unfolding, exposure of surface hydrophobic groups, and orderly aggregation, forming a dense cross-linked gel network. When the Maillard reaction times increased, especially for 90 min, the gel strength and water-holding capacity of the SPI–CMC conjugate gels were significantly increased, along with a denser microstructure. Compared with the SPI and SPI–CMC mixture, SPI–CMC conjugate gels with 60 and 90 min reaction times exhibited notably increased viscosity and storage modulus (G′), as well as better structural recovery characteristics. The above physicochemical property improvements markedly enhanced the riboflavin encapsulation efficiency and riboflavin delivery ability of SPI–CMC conjugate gels, improving the ability to protect riboflavin from photodegradation and slowly releasing riboflavin in the simulated intestinal environment. Hence, SPI–CMC conjugate gels have significant potential for the delivery of nutrients.