Effects of Catechins on Structural, Functional and in Vitro Digestion Characteristics of Soybean Protein Isolate under Spray Drying

After the commercial soybean protein isolate (SPI) treated by high-temperature spray drying, the proteins were prone to undergo a certain degree of denaturation and aggregation, which reducing the solubility and other functional properties. The present study was aimed to investigate the interaction between different concentrations of catechins and SPI under spray drying treatment and the effects on the structural and functional properties of proteins. The results showed that the loading rate and loading content of catechin increased gradually with the increasing of catechin content, and the surface hydrophobicity and sulfhydryl content decreased gradually after the combination of SPI and catechin. The functional characteristics of spray drying SPI were improved after interacted with catechin. When the addition of catechin was 1%, the solubility of SPI was increased by 36.4%, and the emulsifying property and emulsifying stability were increased by 13.7% and 14.3% respectively. The hardness of gel was increased by 43.6% with the addition of 0.25% catechin. Correlation analysis showed that the network structure of gel mainly depended on disulfide bonds, followed by hydrogen bonds and ionic bonds. Furthermore, the storage modulus of gel rheological properties was significantly higher than that of other treatment groups (P < 0.05). It was found by atomic force microscope that the microstructure of the gel changed to homogeneous and dense in each group of proteins with the complexation of catechin. The addition of catechin at 0.25% could promoted minimal aggregation of gel when compared to the other samples. However, the interaction between catechin and protein led to the decrement of the digestibility of spray dried SPI. These results showed that catechin prevented the heat-induced aggregation and improved the structural and functional properties of SPI after spray drying.