Enzymatic hydrolysis of by-products from the fish-filleting industry; chemical characterisation and nutritional evaluation

Fish frames without heads from Atlantic cod and Atlantic salmon were proteolysed with the industrial enzymes neutrase®, alcalase® and pepsin for 1, 15, 30, 45, 60, 90 and 120 min. After 120 min of hydrolysis, salmon treated with alcalase and cod treated with pepsin yielded significantly (p < 0.05) higher protein recoveries (67.6 and 64% respectively) as compared to salmon treated with neutrase or pepsin and cod treated with neutrase or alcalase (53–62%). To minimise bitterness in the fish hydrolysates, kojizyme™ was added after 120 min of pre-hydrolysis with alcalase, and the hydrolysis was run for additional times of 120, 240, 360, 480, 600 and 720 min. Protein recovery did not change significantly during the hydrolysis with kojizyme, but the degree of hydrolysis increased significantly (p < 0.01) in both the cod and salmon hydrolysates. A hydrolysate from cod treated with alcalase (150 min) followed by treatment with kojizyme (510 min) was produced. The final hydrolysate was freeze-dried to a fish protein hydrolysate (FPH) and chemically characterised. The nutritional value of the FPH was established in an experiment with rats. Inclusion of 10% FPH-N showed significantly (p < 0.05) higher nutritional value as compared to rats fed higher inclusion levels of FPH.