Enzymatic Hydrolysis and Characterization of Protein Concentrate Obtained From Mechanically Separated Meat of Nile Tilapia ( <i>Oreochromis niloticus</i> )

The valorization of mechanically separated meat (MSM) from Nile tilapia through enzymatic hydrolysis can convert an underutilized co-product into functional ingredients; however, a practical balance between the degree of hydrolysis (DH) and techno-functional performance remains underexplored. This study aimed to optimize hydrolysis conditions and clearly define the treatments, enzyme (alcalase or papain), concentration (0.3975%-1.1025%), and time (0.385%-4.615 h), and to characterize the resulting fish protein hydrolysates (FPHs) in terms of solubility and emulsifying properties. A central composite rotatable design was used to evaluate the specified factors. Responses included solubility at pH 5.0, 7.0, and 9.0, emulsifying activity index (EAI), emulsion stability index (ESI), and qualitative FTIR. The optimized condition with alcalase (1.1025%, 4.615 h) yielded a DH of 13.80%, while the design-center condition yielded 2.06%, accompanied by improved solubility at neutral/alkaline pH and higher EAI/ESI. Papain tended to generate higher DH ranges in certain conditions but exhibited lower solubility near its isoelectric point (pI). Principal component analysis captured enzyme-dependent patterns linking DH and solubility. Collectively, the results indicate that tuning enzyme specificity, dose, and time enables the production of tailored FPH with balanced functionality, making it potentially suitable for use as clean-label emulsifiers or for protein enrichment, thereby supporting circular economy strategies by upcycling MSM. Because in-depth structural assays (e.g., peptide profiling, amino acid composition, zeta potential) were beyond the scope, we identify them as future steps to strengthen structure-function interpretation and validation in real food matrices. Standardized reporting of units (% DH) and clear treatment definitions can facilitate comparability across studies and accelerate the translation of findings.