Functional improvement and characterization of protein hydrolysates prepared by the fermentation of irradiated tilapia skin

Gamma irradiation (γ-irradiation) sterilizes and modifies proteins. This study aimed to enhance the performance of protein hydrolysates of fermented tilapia fish skin using irradiation. The results showed that γ-irradiation could effectively kill harmful microorganisms in fish skin at 6 kGy. Irradiation at 1–6 kGy dose disintegrated the internal structure of fish skin proteins, thus increasing the degree of hydrolysis after fermentation by Bacillus subtilis L4; however, irradiation at 9–12 kGy caused cross-linking and aggregation of fish skin proteins. The solubility, and water and oil holding capacity of the protein hydrolysates were significantly improved compared to those of the non-irradiated sample. The maximum emulsifying activity (164.61±16.28 m²/g), foaming activity (91.13±2.30 mL), and surface hydrophobicity index (5766.43±770.56) were observed in the protein hydrolysates fermented from fish skin irradiated at 12 kGy. The antioxidant activity of the protein hydrolysates increased with increasing irradiation doses. This suggested that the functional properties and antioxidant activity of protein hydrolysates from fish skin fermentation can be improved by appropriate irradiation pretreatment, providing a feasible method for improving the utilization and quality of proteins in fishery waste.