Comparative Rates of IMP Degradation in Unfrozen and Frozen‐and‐Thawed (Slacked) Fish

Abstract

SUMMARY— The comparative rates of IMP degradation between fresh and frozen‐and‐thawed (slacked) fish were compared on six different species of fish. Several factors that could contribute to a rate change of IMP degradation were evaluated. These included freezing temperatures, time in frozen storage, pre‐ and post‐rigor freezing, and method of killing the fish.English sole and rainbow trout showed slight increases in the rate of IMP degradation when they were frozen and then thawed within 48 hr. Silver salmon and halibut that were frozen and then thawed within 48 hr showed no change in the rate of IMP degradation. Halibut, however, that was frozen and stored at −20°F for 3 months showed a slight decrease in the rate of IMP degradation after it was thawed; but king salmon handled under the same conditions did not.The method of kill or freezing the fish either pre‐ or post‐rigor did not alter the rate of IMP degradation after the fish was thawed.No loss of IMP occurred in fish (halibut) stored at −20°F. Over one‐third of the original IMP content was lost in halibut stored at +15°F after 3 months of storage.These results show that there is no significant difference in the rate of IMP degradation between fresh and slacked fish. The flavor‐contributing effect of IMP in slacked fish therefore should be the same as in fresh fish, provided the fish was frozen and stored at or near a temperature of −20°F.