PROTEIN AUTOLYSIS RATES AT VARIOUS pH'S AND TEMPERATURES IN 



HAKE, Merluccius productus, AND PACIFIC HERRING, Clupea harengtis pallasi, 



AND THEIR EFFECT ON YIELD IN THE PREPARATION 



OF FISH PROTEIN CONCENTRATE 



Barbara Koury, John Spinelli, and Dave Wieg' 



ABSTRACT 



The rate of protein autolysis at temperatures ranging from 30° to 80° C and at pH's ranging from 3.0 

 to 7.0 were determined on hake and Pacific herring. Autolysis rates were generally greatest at acidic 

 pH's and began to decrease after temperatures exceeded 50° C. Autolysis rates were much greater in 

 hake than in Pacific herring. The yield of fish protein concentrate prepared from hake showed a close 

 inverse correlation to the degree of autolysis. 



The production of fish protein concentrate 

 (FPC) requires a process that efficiently re- 

 moves oil and water from the fish and provides 

 high yields of protein. Although FPC can be 

 prepared by several different methods (Knobl, 

 1967), the most effective procedures developed 

 to date are based on systems in which commin- 

 uted fish is successively extracted with a suitable 

 solvent system. 



Dambergs (1969), in studying the extracting 

 efficiency of isopropyl alcohol (IPA) -water mix- 

 tures in producing FPC from herring, found 

 that low molecular weight compounds were 

 readily removed with these solvent systems. 

 Fish flesh and viscera contain highly active ca- 

 theptic enzjTTies which utilize fish tissue as a 

 substrate, forming low molecular weight pro- 

 tein degradation products (Siebert, 1962; Ting, 

 Montgomery, and Anglemeier, 1968). Normal 

 autolysis of fish tissue during storage has been 

 related to decreased yields in FPC production. 

 Dubrow, Brown, Pariser, Miller, Sidwell, and 

 Ambrose (1971) found that when ice-stored fish 

 was u.sed to make FPC, the yield was signifi- 



' ^rational Marine Fisheries Service Technological 

 Laboratoij, ''725 Montlake Boulevard East, Seattle, 

 Wash. 98102. 



Manuscript received September 1970. 



FISHERY BULLETIN: VOL. 69. NO. I, 1971. 



cantly lower than the yield obtained when FPC 

 was prepared from freshly caught fish. In an- 

 other study by Dubrow and Hammerle (1969), 

 in which FPC was prepared from samples of 

 comminuted fish held in 91 ''r IPA for various 

 lengths of time, similar results were obtained. 



Preliminary studies in this laboratory, on the 

 development of an aqueous process for FPC pro- 

 duction, indicated that under certain conditions 

 significant protein losses may also occur during 

 actual processing pi'ocedures as a result of en- 

 zymatic hydrolysis. 



In solvent extraction procedures for FPC pro- 

 duction, the yield of product (excluding physical 

 losses) is dependent upon the amount of pro- 

 teinaceous material soluble in the extracting 

 solution. While losses can be controlled to some 

 extent by the choice of solvent systems, the 

 possibility of losses due to enzymatic degradation 

 of protein must also be considered. 



The purposes of this study were as follows: 



1. To determine the eflfect of pH, time, and 

 temperature on the rate of protein autolysis 

 in two species of fish that are considered for 

 use in the ijroduction of FPC. 



2. To determine the effect of autolytic ac- 

 tivity on FPC yields. 



241 



