Thermal inactivation characteristics of acid and alkaline phosphatase in fish and shellfish

To provide information about the roles of acid and alkaline phosphatase (ACP, ALP) activities, as the degree of working indicators of marine foods, the effect of heating (55 and 65 °C) on phosphatase activities, in the edible part of selected species was investigated. Twenty-nine out of 49 fresh fish, shellfish and crustacea samples, such as mackerel Scomber japonicus, showed maximum activity at pH 5 or 6 and very low activity at pH 11. The other 20 species showed various ALP activities. Particularly, in the case of gurnard Lepidotrigla microptera, sea robin Chelidonichthys spinosus and Glyptocephalus stelleri, a flounder, the ALP activity was higher than the ACP activity. The phosphatase activities were reduced to 10% or less of the activity in unheated samples by heating at 55 °C for 10 min. The heat-stability of ALP in intestines was far higher than that in dorsal muscle. These results suggest that the measurement of ACP and ALP activities in marine foods can be used as a quality check.