Yuhao Zhang

Background: Transglutaminase-crosslinked collagen gel (CHG) is a collagen product cross-linked with transglutaminase (TGase) that exhibits good thermal stability and has potential applications in functional food formulations. However, it remains unclear whether the gelation of CHG alters the metabolic fate of collagen-derived bioactive peptides in the gastrointestinal tract and their distribution within the body. Methods: This study investigated the retention of CHG in the gastrointestinal tract of male C57BL/6J mice, as well as its serum peptide levels and antioxidant activity. Results: Compared with unhydrolyzed (CNS) and hydrolyzed collagen (CHS) sols, CHG significantly prolonged gastric retention and slowed intestinal transit, while gastric contents exhibited larger particle sizes and a more sustained release of protein. The CHG also increased the expression of genes associated with Cajal interstitial (ICC) cells in the gastric antrum (HCN1, Trpm7, CX43, and c-kit) and prolonged the secretion of leptin, cholecystokinin, serotonin, and vasoactive intestinal peptide. Serum peptide analysis showed that the concentrations of most collagen dipeptides and tripeptides, peaked between 0.5 and 1.5 h and then gradually declined; notably, the concentration of Pro-Hyp in the CHG group remained higher than that in the control group at 3 h, indicating prolonged serum appearance. Serum peptides from CHG group (particularly Pro-Hyp) exhibited total antioxidant capacity and hydroxyl radical scavenging activity, and the mixed-peptide solution significantly reduced the accumulation of reactive oxygen species in H₂O₂-induced skin fibroblasts (p < 0.001). Conclusions: These findings suggest that the cross-linked structure of CHG alters gastrointestinal metabolic processes and is associated with the persistent presence of collagen-derived dipeptides and tripeptides in serum.

Pork belly is widely favored for its alternating fat-lean layers, yet the raw material characteristics of different cuts-upper (UPB), middle (MPB), lower (LPB), and second-knife meat (SKM)-remain unclear. This study selected twice-cooked pork belly (TPB) as the model dish to systematically compare the texture, collagen, microstructure, and flavor of four cuts from raw to cooked stages. Texture analysis showed that the skin layer was mainly related to collagen, while the fat layer was influenced not only by collagen content and composition but also by the extracellular matrix network, as revealed by Masson staining. Lean meat texture was primarily determined by its proportion, resulting in 57.55 ~ 124.45% higher chewiness in SKM. Flavor and precursor analysis revealed that UPB was characterized by higher proline and C20:4n6 and was associated with higher relative abundance of sweet/citrus aldehydes. MPB generated fatty aroma linked to C18:1n9c. LPB delivered complex meaty/roasted flavors from C18:1n9c, C18:2n6c, and Phe. SKM exhibited a flavor profile dominated by 2,3-butanedione due to its high branched-chain amino acid content. Furthermore, biplot analysis elucidated the relationships between raw material characteristics and final quality attributes, providing a theoretical basis for selecting the pork belly cuts in industrial production.