Changes in acid and alkaline phosphatase activities during the spoilage of raw muscle from horse mackerel Trachurus japonicus and gurnard Lepidotriga microptera

The aim of this work was to provide information on the role of acid phosphatase (Acp) and alkaline phosphatase (Alp) activities as spoilage indicators of raw fish. Horse mackerel Trachurus japonicus, a red-flesh fish, and gurnard Lepidotriga microptera, a white-flesh bottom fish, were stored at 4 °C. The aerobic bacteria count (APC) of horse mackerel skin increased from 103 to 107 CFU/cm2 in seven days, the Alp activity increased about from 10 to 150 nmol p-nitrophenol/min/g tissue with increase of volatile basic nitrogen (VBN), an index of fish spoilage. The APC of gurnard skin also reached 107 CFU/cm2 after 8 days’ storage. The Alp activity was twice that of the Acp activity in the fresh gurnard and the activity decreased slightly during the initial 4 days and increased from four days’ storage.