The Effect of Protease Inhibitors on Proteolysis in Parasitized Pacific Whiting, Merluccius Productus, Muscle

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 productus, 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 Nethylmaleimide. 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 productus, 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 portions) where the temperature of inactivation is achieved before proteolysis destroys the texture IUtilization Research Division Northwest and Alaska Fisheries Center, National Marine Fisheries Service, NOAA, 2725 Montlake Boulevard East, Seattle, WA 98112. Manuscript accepted November 1981. FISHERY BULLETIN: VOL. BO. NO.2. 1982. of the fish (Patashnik et al.). 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.