Comparative Assessment of Commercial Collagen Peptides Following Simulated Gastrointestinal Digestion: Structural Stability, Bioactivity, and Digestibility

Background/Objectives: Commercial collagen peptide products may differ in their structural characteristics and in vitro biological properties depending on manufacturing processes and hydrolysis conditions. However, comparative studies integrating simulated gastrointestinal digestion with structural, physicochemical, and cell-based analyses remain limited. This study comparatively evaluated commercially available bovine collagen peptide products marketed in Türkiye before and after simulated gastrointestinal digestion. Methods: Collagen peptide samples were characterized before and after simulated gastrointestinal digestion by determining hydroxyproline content, degree of hydrolysis (DH), molecular weight (MW) distribution, antioxidant activity, and fibroblast responses to investigate digestion-induced structural and biological changes. Results: Significant differences were observed among the evaluated products in hydroxyproline content, degree of hydrolysis, molecular weight distribution, antioxidant activity, and fibroblast responses. Simulated gastrointestinal digestion further hydrolyzed all collagen peptide samples, although the extent of structural modification varied among products. Antioxidant responses also differed following digestion, with some products maintaining relatively stable radical scavenging activity, whereas others exhibited increased or decreased antioxidant responses. Cell viability assays demonstrated that all collagen peptide samples were non-cytotoxic toward L929 fibroblasts under the experimental conditions. Conclusions: The findings indicate that simulated gastrointestinal digestion influences the structural characteristics and in vitro biological responses of commercial collagen peptide products to different extents. The observed differences among products suggest differential in vitro bioactivity associated with their structural characteristics and digestion behavior. Nevertheless, these findings are limited to in vitro observations and require confirmation through peptide characterization, bioavailability studies, animal models, and well-designed clinical investigations before conclusions regarding physiological efficacy or potential health benefits can be drawn.