Collagen Hydrolysate Prepared from Fish Skin as a Functional Biopolymer in Biomimetic Cosmetic Formulations

Collagen is one of the main constituents of cosmetic formulations because of its moisturizing, regenerating, and film-forming properties. The aim of the present study was to obtain biocompatible collagen hydrolysates from Hypophthalmichthys molitrix skin, using a neutral inexpensive hydrolysis process involving low temperature (135 °C) and pressure values (315 kPa) and by using various pretreatment procedures (in order to eliminate the scales, fat, and meat). Comprehensive characterization of the hydrolysate samples confirmed their high purity, evidenced by a protein content exceeding 10%, undetected ash levels, and a pH between 6 and 7. This was further supported by optical microscopy and SEM imaging, which revealed the characteristic fibril structure. Additionally, FTIR analysis and CD spectroscopy verified a specific random coil structure and the complete absence of the triple helix characteristic of denatured collagen. EDX results confirmed the presence of C, O, N, and traces of S in all collagen hydrolysate samples. The results of the microbiological analysis for E. coli and S. aureus show either the complete absence or negligible amounts of fungi and bacteria in all hydrolysate samples, thereby demonstrating the effectiveness of the extraction process. The in vitro biocompatibility assessment established a non-cytotoxic concentration range between 1.25 mg/mL and 10 mg/mL for the tested samples, with cell viability above 70% and LDH release below 5%. Furthermore, clinical patch tests of the obtained fish collagen hydrolysates revealed no irritation reactions. Neutral hydrolysis of silver carp skin collagen hydrolysates with determined characteristics and favorable biocompatibility proves to be suitable for cosmetic applications.