THE EFFECT OF PROTEASE INHIBITORS ON PROTEOLYSIS IN 

 PARASITIZED PACIFIC WHITING, MERLUCCIUS PRODUCTUS, MUSCLE 



Ruth Miller and John Spinelli 1 



ABSTRACT 



Since the enactment of the Fishery Conservation and Management Act of 1976, the U.S. fishing 

 industry has intensified its interest in Pacific whiting, Merluccius products, as an additional food 

 resource. In some fishing areas, Pacific whiting is infected with a protozoan parasite, Myxosporidia 

 kudoa, which produces a proteolytic enzyme that degrades the textural quality of muscle as it is 

 processed or cooked. 



Several enzyme inhibitors were evaluated for their potential to inactivate the enzyme, thereby 

 preserving the texture of the fish during processing. It was found that protease inhibitors such as 

 those found in egg white, potato, and soy and lima beans were ineffective as inhibitors. Compounds 

 that react with sulfhydryl groups, on the other hand, were found to be active inhibitors. These 

 compounds include hydrogen peroxide (free and alkaline), potassium bromate, iodoacetate, and N- 

 ethylmaleimide. The most promising results were obtained with potassium bromate or 

 combinations of dibasic phosphate peroxide and potassium bromate. These reagents mixed into 

 ground parasitized pacific whiting muscle inhibited proteolysis sufficiently during frozen storage 

 and later cooking to maintain texture comparable with nonparasitized fish. 



The Fishery Conservation and Management Act 

 of 1976 has intensified the interest of the fishing 

 industry in Pacific whiting, Merluccius produc- 

 tus, as an additional food resource. Although 

 Pacific whiting has been extensively fished by 

 the Russian and Polish fishing fleets, it has 

 attracted only slight commercial interest in the 

 United States, primarily because its texture and 

 color are somewhat less desirable than that of 

 other gadoid species such as cod and haddock. In 

 1970, Dassow et al. observed that the textural 

 change in cooked Pacific whiting was due to the 

 presence of a protozoan parasite, Myxosporidia 

 kudoa. This parasite produces a proteolytic 

 enzyme capable of breaking the chemical bonds 

 of the muscle fibers which are responsible for the 

 characteristic texture of fresh fish. The activity 

 of the enzyme increases as the temperature 

 increases. Thus, during conventional processes 

 such as baking, broiling, or pan frying, the 

 gradual increase in heat enhances proteolysis 

 until the product reaches the temperature of 

 inactivation of the enzyme. One method of 

 handling the problem of the parasitic enzyme is 

 rapid cooking (deep-fat frying of sticks and por- 

 tions) where the temperature of inactivation is 

 achieved before proteolysis destroys the texture 



'Utilization Research Division Northwest and Alaska 

 Fisheries Center, National Marine Fisheries Service, NOAA, 

 2725 Montlake Boulevard East, Seattle, WA 98112. 



of the fish (Patashnik et al. 2 ). Another possibility 

 would be to inactivate the enzyme with an 

 inhibitor. 



In the work presented here, several enzymic 

 inhibitors were evaluated to determine their 

 effectiveness in inhibiting proteolysis in Pacific 

 whiting muscle. The concentration of enzyme 

 inhibitor sufficient to prevent organoleptic 

 textural alteration was also determined. 



METHODS 



Pacific whiting were caught off the coast of 

 Astoria, Oreg., by commercial trawlers, filleted 

 and frozen within 24 h, and stored at — 20°C. 



The presence of the parasite was determined 

 directly by visual evidence of black and white 

 spores, by microscopic identification of the 

 spores, or, indirectly, by baking a segment of 

 muscle in a covered container for 20 min at 

 162°C. Soft or mushy muscle indicated the 

 presence of the parasitic enzyme. 



To ascertain the effects of enzyme inhibitors 

 under uniform conditions, tests for proteolytic 

 activity were carried out on diluted blends of fish 



Manuscript accepted November 1981. 

 FISHERY BULLETIN: VOL. 80. NO. 2. 1982. 



2 Patashnik, M.. H.S. Groninger. H. Barnett, G. Kudo, and B. 

 Koury. 1981. Pacific coast whiting (Merlucciuit productus). 

 I. Abnormal muscle texture caused by myxosporidian-induced 

 proteolvsis. In prep., 34 p. Northwest and Alaska Fisheries 

 Center* Natl. Mar. Fish. Serv., NOAA, 2725 Montlake Blvd. 

 E., Seattle. WA 98112. 



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