A bioretanning agent was developed as an alternative to conventional synthetic retanning agents to pave the way for sustainability in the leather industry. Tanned solid waste shavings obtained from leather processing was utilized to produce a proteinic sub-structure for constitution building block of the bioretanning agent's backbone. The protein hydrolyzates were acquired with different molecular weights and the hybrid biopolymers were obtained by grafting the hydrolyzates with acrylic acids (AAc) and acrylamides (AAm). To evaluate the properties imparted by the designed bioretanning agent, it was incorporated into the leather in the retanning processes and compared to the control samples fabricated with conventional procedures. Penetration of hybrid biopolymer into the matrix for retanning was achieved easily, and using low and high molecular weight biopolymers have been recorded by 20% and 23% of improvement on the mechanical performance of the leather samples, respectively. The ratio of the hydrolyzate and AAm/AAc was found to be fitted at 1:2 for both. Furthermore, as per the evaluation of the leathers retanned by novel biopolymer, the results were promising in terms of technical viability and revealed that the biopolymer usage could enhance the mechanical performance of the leather while benefiting from the waste-to-wealth approach.

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.