A comparative study on the physicochemical characteristics and protein digestibility of tofu induced by magnesium chloride or combined with transglutaminase

Summary In this study, tofu was prepared through the addition of transglutaminase (TGase) for pre‐crosslinking at varying durations (1, 2 and 3 h), followed by the addition of magnesium chloride (MgCl 2 ) to soymilk. The physicochemical properties and protein digestibility were analysed. Results indicated that, with the prolongation of TGase pre‐crosslinking time, the zeta‐potential absolute value and the average particle size of soymilk increased gradually. In contrast, the pH value remained unchanged ( P > 0.05), suggesting that the colloidal stability of soymilk improved with TGase treatment. Both the water‐holding capacity (WHC) and gel strength of tofu gels exhibited a first increasing and then decreasing trend with prolonged pre‐crosslinking time. Notably, the highest WHC and hardness values of tofu gels prepared by adding MgCl 2 after pre‐crosslinking with TGase for 1 h were 96.5 ± 0.5% and 363.9 ± 28.3 g, respectively. Subsequently, in vitro simulated gastrointestinal digestion of tofu samples prepared under this condition was conducted to determine changes in soluble protein content, small peptide content and protein hydrolysis spectrum. Gastric and intestinal digestion phases were the primary stages of protein hydrolysis, and the bioavailability of proteins in TGase+MgCl 2 ‐induced tofu was higher than in MgCl 2 ‐coagulated tofu. Therefore, tofu prepared through TGase pre‐treatment was more conducive to soybean protein digestion and absorption.