Comparison of 5'-inosine monophosphate and p-nitrophenyl phosphate degrading activities among red, pink, and white muscle fibers of cultured carp

As part of a study to clarify the differences in the temporal change in K-value among fish species, the temporal change in K-value and the 5′-inosine monophosphate (5′-IMP) and p-nitrophenol phosphate (p-NPP) degracling activities in the red, pink, and white muscle fibers in the dorsal muscle of the carp were compared. The temporal change in K-value was fastest in red, followed by pink, and white muscle fibers, at both 0°C and 32°C. Moreover, the 5′-IMP and p-NPP degrading activities were highest in red, followed by pink, and white muscle fibers at near optimum pH concentrations. The 5′-IMP degrading activity at pH 7.0 had a positive correlation with the increasing rate of K-values at 32°C for all types of muscle fibers. These results suggest that differences in increasing rates of K-values between red, pink, and white muscle fibers corresponded to the 5′-IMP degrading activities.