Optimization of enzymatic hydrolysis of Alaska pollock frame for preparing protein hydrolysates with low-bitterness

To obtain hydrolysates with high nitrogen recovery (NR) and low-bitterness, Alaska pollock frame (APF) was treated by high-pressure cooking at 120 °C for 30 min and hydrolyzed with ten different commercial proteases. MEAP (Mixed enzymes for animal proteolysis) hydrolysates exhibited the best characteristics (high NR and low bitter taste), which had high content of oligopeptides with molecular mass lower than 1355 Da. The optimum hydrolysis conditions using MEAP were determined as follows: temperature 45 °C, hydrolysis time 300 min, enzyme to substrate ratio (E/S) of 1.2 g/100 g, liquid-solid ratio 6:1, and initial pH 8.0. The NR and DH (degree of hydrolysis) of the hydrolysates were 76.89% and 18.09%, whereas the bitterness value was lower than that of 0.1 g/L tea alkaloid. The essential amino acid chemical scores (CS) were greater than 0.8 (0.8–1.4) in pollock frame hydrolysates (PFH) which exhibited high nutritional value. It showed that APF and PFH as high-quality protein source may have a wide application.