Determination of collagen types and mineral contents in fish skin and collagen-containing skin-derived protein hydrolysates before and after <i>in vitro</i> simulated digestion

An <i>in vitro</i> digestion model was established to characterize the types of collagens in skin of cod, white fish, and salmon as well as their collagen-containing skin-derived protein hydrolysates (CSPH) before and after digestion. Moreover, the mineral content and their bioaccessibility were evaluated. Finally, the presence of heavy metals was evaluated to assess the safety of these products. The results showed that white fish protein exhibited a high digestibility, reaching up to 92%. Among the collagen products, salmon collagen had the highest digestibility (∼73%). Protein identification revealed that the emPAI of type I collagen in digested skin and CSPH was higher than that of undigested samples. In addition, raw skins had higher contents of P, K, Ca and Mg, and the mineral content of CSPH was lower than that of unprocessed skins. Among the minerals studied, Ca and Cu showed the highest bioaccessibility in raw skin cod, being 32% and 26%, respectively. The bioaccessibility of Cu in raw skin salmon was also higher (∼34%). Moreover, in CSPH, Mg, K and Cu can be easily digested and absorbed. Regarding heavy metals, As and Pb were below the respective safe limits in all raw skins and CSPH, while Hg and Cd were not detected in the fish CSPH. Fish-derived collagen has gained significant attention due to its numerous health benefits, high bioavailability, and superior sustainability compared to animal collagen. Moreover, different types of collagens offer distance roles and advantages in the body. However, there are limited reports on how collagen structure and type may change during the digestive process. This study seeks to deepen our understanding of the economic value of fish collagen, as well as the mechanisms of its absorption and digestion. By investigating processes, the research aims to provide a clearer insight into the physiological effects of fish-derived collagen, which can inform the development of tailored collagen supplementation programs based on specific health needs.