Enzymatic protein hydrolysis of residual raw material from Atlantic cod: Selectivity of proteases, outcome and bioactivities

Abstract

Global trends show that interest in fish products and fish consumption are increasing, while marine fishery resources are decreasing. Fish processing industry produces a high amount of residual raw materials that have nutritious proteins and other valuable compounds. An optimization of residual raw materials’ utilization can help meet the growing demand for fish products and help reduce environmental problems. A promising valorization method is enzymatic protein hydrolysis. In this project, enzymatic protein hydrolysis was performed to produce protein hydrolysates from complex material of Atlantic cod heads. Three types of material from cod heads (muscle, skin and bone) were hydrolyzed by 23 different proteases. The produced hydrolysates were analyzed and evaluated based on yield, molecular weight (determined by SEC and SDS-PAGE), selectivity of proteases towards collagen and myofibrillar proteins (selectivity ratio), and bioactivity properties (anti-proliferative, antioxidant and anti-inflammatory). It was determined that the highest yield from muscle was produced by Tail 191, from skin by Tail 194, and from bone by Tail 190. Different proteases produced hydrolysates with different average MW. Notably, Tail 189 produced hydrolysates with the lowest average MW from all three types of raw material. The SDS-PAGE patterns of the hydrolysates from skin indicated that Tail 193 and Endocut 01 might have selectivity towards peptide bonds they cleave. The selectivity ratio identified that Endocut 01 had the highest selectivity towards myofibrillar proteins and Flavourzyme was the only enzyme selective to collagen. The results of bioactivity assays showed no antiproliferative or anti-inflammatory activity of the hydrolysates, however, all hydrolysates demonstrated antioxidant activity. The hydrolysates made from muscle showed higher antioxidant activity than the hydrolysates prepared from skin and bone. Based on the results, conditions for a scale-up experiment (from 5 g of raw material to 250 g) were suggested, which included recommendation of several enzymes per material, adjustment of temperature to optimal for each enzyme, monitoring of hydrolysis process and determination of ash content in the product.