In Vitro Pepsin Digestion Characteristics of Silver Carp (Hypophthalmichthys molitrix) Surimi Gels with Different Degrees of Cross-Linking Induced by Setting Time and Microbial Transglutaminase

Surimi gels are favored for their abundant proteins and unique taste. In this study, the pepsin digestion behaviors of surimi gels with different degrees of cross-linking induced by microbial transglutaminase (MTGase) and different setting times were investigated. For gels without (CK group) and with (TG group) MTGase, the slowest digestion rate (tM/2 = 20.13 and 79.19 min for CK and TG group, respectively), the least amino acid concentration (5.32 and 3.73 μmol/mL for CK and TG group, respectively), and the peptide amounts (1355 and 1788 for CK and TG group, respectively) were obtained at a moderate setting time (1–4 h) with the finest microstructure. However, the excessive setting time (8–12 h) formed an inhomogenous network, which accelerated the hydrolysis of gel proteins (tM/2 = 9.40 and 52.33 min for CK and TG group, respectively) and produced more amino acids (6.63 and 5.15 μmol/mL for CK and TG group, respectively) and peptide amounts (1644 and 2143 for CK and TG group, respectively). The above results also demonstrated that the presence of MTGase strengthened the compactness of gels as well as slowed down the digestion process with the release of less amino acids but more peptides. A large proportion of unique peptides were from the tail domain of myosin heavy chain. The discrepancy in bioactive peptides between different gels might be reduced in the subsequent intestinal digestion according to the in silico methods, demonstrating the diminished difference in the gastrointestinal digestion process in the aspect of releasing functional peptides. This study provides the theoretical basis and guideline in the field of gelation food digestion and surimi food industry to produce healthier surimi-based food.