Evaluation of antibacterial and antioxidant activities of rainbow trout (Oncorhynchus mykiss) skin protein hydrolysate

The present study aimed to investigate antibacterial and antioxidant properties of proteins produced by the enzyme hydrolysis of rainbow trout (Oncorhynchus mykiss) skin produced by alcalase and flavourzyme enzymes. Antibacterial activity of skin protein hydrolysate were done by disc diffusion, agar pit diffusion and microdilution methods. Antioxidant activity of skin protein hydrolysate were investigated by DPPH free radical inhibitory and ferric reducing antioxidant power (FRAP) at three concentrations of 200, 500 and 800 ppm. The results showed that skin protein hydrolysate by alcalase and flavourzyme were not able to inhibit growth of Pseudomonas aeruginosa and Staphylococcus aureus strains (standard strains) but they had antioxidant activity. Degree of hydrolysis in SPH produced by flavourzyme was more than the alcalase (43.83 ± 1.75   ). The radical DPPH inhibitory power of SPH produced by alcalase was significantly higher than the flavourzyme (p<0.05). However, FRAP results in SPH produced by flavourzyme was significantly higher than the alcalase (p<0.05). By increasing protein concentrations, the antioxidant properties of the SPH increased. In the event that, the synthetic anti-oxidants BHA and BHT had radical DPPH inhibitory power and ferric reducing power higher than alcalase and flavourzyme hydrolyzed proteins.The results showed that the hydrolyzed proteins less than 3 kD of Rainbow trout skin could not inhibit the growth of bacteria but they can be offered as a natural antioxidant in the preparation of foods and health products.