Protein isolation from gutted herring (Clupea harengus) using pH-shift processes.

Herring ( Clupea harengus ) and other pelagic fish species are mainly used for fish meal and oil production and not for human consumption. In this study, acid pH-shift processing and alkaline pH-shift processing were used to isolate proteins from whole gutted herring with the aim to investigate the potential use of herring proteins as a food ingredient. The acid and alkaline processes gave rise to similar protein yields, 59.3 and 57.3%. The protein isolates from both processes had a significantly (p < 0.05) whiter color and higher protein and lower lipid contents than the starting material. The removal of ash was >80% for both processes, with a trend (p = 0.07) toward higher removal during the alkaline process. Also, Ca and Mg removal was significantly (p < 0.05) higher during the alkaline process. The isolated proteins from the acid process contained myosin degradation products and had a lower salt solubility than proteins from the alkaline process. Both protein isolates had an amino acid profile meeting the recommendations for adults according to FAO/WHO/UNU and could produce a surimi gel of medium strength. The results show that pH-shift processing could be a valuable method for the production of functional food proteins from gutted herring.