Determination of the Quality of Oil Obtained from Protein Hydrolysate Produced Using Rainbow Trout (Oncorhynchus mykiss) By-Products

The growing demand for sustainable food sources requires the efficient use of aquaculture by-products. This study aimed to optimize enzymatic hydrolysis conditions for the simultaneous recovery of fish protein hydrolysate (FPH) and oil from rainbow trout (Oncorhynchus mykiss) processing by-products. Hydrolysis was performed at different temperatures (30–50 °C), enzyme concentrations (0.5–1.5%), and durations (30–90 min), and the optimal conditions were determined as 40 °C, 1% enzyme concentration, and 60 min. Under these conditions, oil yield reached 11.46%, while quality indices remained within acceptable limits (peroxide value: 1.78–3.47 meq O2/kg; thiobarbituric acid reactive substances: 0.41–1.41 mg MDA/kg; free fatty acids: 0.27–4.12%). Fatty acid analysis revealed 22.5% saturated, 46.31% monounsaturated, and 23.52% polyunsaturated fatty acids, including notable levels of EPA and DHA. The protein hydrolysates obtained under optimized conditions contained 22.61% protein and essential amino acids, accounting for 52.4% of the total amino acid content, confirming their high nutritional value. Overall, the findings demonstrate that rainbow trout by-products can be effectively valorized through enzymatic hydrolysis to produce oil and protein hydrolysates of acceptable quality, which may serve as alternative ingredients for food and feed applications.