Effects of Various Salts on IMPase Activity and IMP Quantity in Coho Salmon, Oncorhynchus kisutch (Walbaum 1792), Salmonidae

Coho salmon, Oncorhynchus kisutch (Walbaum 1792), Salmonidae is a fast growing species that is reared for food worldwide. After harvest, coho salmon is often salted and stored. When a fish dies, adenosine triphosphate (ATP) is degraded in the muscles to inosinic acid (IMP), the taste component that gives the fish its flavour. During storage, IMP is degraded to non-taste components by the IMP-degrading enzyme (IMPase), resulting in a loss of flavour. Therefore, it is crucial to suppress IMPase activity in order to maintain IMP levels. In this study, IMPase activity was investigated at various pH levels and with salts used for storage of coho salmon, along with the resulting amount of IMP and changes in pH level. The results showed that the amount of IMP significantly decreased from 9.5 µmol·g -1 on day 0 to 4.6 µmol·g -1 on day 4 (p< 0.05) in fish stored at 4 o C in our laboratory but the pH level remained constant at 6.1±0.1. The enzyme activity was the highest at pH 6 and decreased sharply at pH 7-8. The salts that effectively maintained IMP in coho salmon were in the following order, MgSO4 and Na2SO4 at pH 4-5; MgCl2, CaCl2, MgSO4, and Na2SO4 at pH 6; and NaCl, CaCl2, and Na2SO4 at pH 7-8. These results indicated that the amount of IMP present after several days of storage was significantly higher with the addition of these salts.