Optimizing angiotensin I-converting enzyme inhibitory activity of Pacific hake (Merluccius productus) fillet hydrolysate using response surface methodology and ultrafiltration.

The in vitro angiotensin I-converting enyzme (ACE) inhibitory activity of Pacific hake hydrolysates was investigated as a function of hydrolysis conditions, starting material variability, and ultrafiltration. Hake fillets were hydrolyzed using Protamex protease under various conditions of pH, hydrolysis time, and enzyme-to-substrate ratio (% E/S) according to a response surface methodology (RSM) central composite design. The hydrolysate produced at pH 6.5, 125 min, and 3.0% E/S had an IC 50 of 165 +/- 9 microg of total solids/mL. ACE-inhibitory activity was not significantly different (P < 0.05) for hydrolysates produced using higher time-enzyme combinations within the model or from fish of different catches. Ultrafiltration (10 kDa molecular mass cutoff) resulted in an IC50 value of 44 +/- 7 microg of peptides/mL, 2.5 times more potent than the commercial product PeptACE Peptides (IC50 = 114 +/- 8 microg of peptides/mL). These results suggest that hydrolysates prepared with minimal fractionation from Pacific hake, an undervalued fish, may be a commercially competitive source of ACE-inhibitory peptides.