Optimization of Enzymatic Hydrolysis of Atlantic Salmon Frame Proteins by Alcalase Using Response Surface Methodology: Degree of Hydrolysis and Nitrogen Recovery

The valorization of salmon farming by-products is an essential strategy within the circular economy. This study optimized the enzymatic hydrolysis of salmon frame proteins using Alcalase 2.5L and response surface methodology (RSM). The effects of temperature (50–60 °C), substrate concentration (50–100% w/w), and protease dose (1–13 mAU/g salmon frames) were evaluated on two key responses: degree of hydrolysis (DH) and nitrogen recovery (NR). The 20 experimental assays showed that substrate concentration and enzyme dosage strongly influenced both responses, whereas temperature had a moderate effect. The fitted models exhibited R2adjusted values above 70% and met statistical assumptions, confirming their predictive reliability. Optimal conditions for maximizing DH were 55 °C, 50% w/w substrate, and 13 mAU/g protease, yielding a predicted DH of 6.65%. In contrast, the highest NR (48.35%) was observed at 50 °C, 50% w/w substrate, and 13 mAU/g protease, indicating that solubilization does not depend solely on hydrolysis intensity. Validation experiments showed no significant differences between predicted and experimental values (p > 0.05), supporting the robustness of the models. These results demonstrate the usefulness of RSM for optimizing enzymatic hydrolysis and advancing sustainable valorization of salmon by-products.