Study of Freshness of Shell-Fish Using Dehydrogenase Activity

The seasonal variations in shell-fish dehydrogenase activity was examined. Dehydrogenase activity in Akagai, Sakiaka, Aoyagi, and Shitakiri had been measured for 20 months. Akagai has no chance. Shelled Akagai is called Sakiaka, which has the viscera removed and then arranged for eating.Aoyagi is shelled Bakagai. Shitakiri is Aoyagi with the viscera removed. Dehydrogenase activity in oyster, both for whole and shelled ones, was measured twice in the winter over a period of 5 months. No seasonal variations in the dehydrogenase activity of Akagai, Sakiaka, Aoyagi and Shitakiri was observed. The variation of dehydrogenase activity in oyster was nearly constant through out the winter.The dehydrogenase activity was 252±54μg/g in Akagai, 183±66μg/g in Sakiaka, 240±78μg/g in Aoyagi, 184±94μg/g in Shitakiri, 1097±243μg/g in oyster with shell, and 825±378μg/g in shelled oyster. These values are considered to be good dehydrogenase activity ratings for fresh shell-fish, Akagai, Sakiaka, Aoyagi, Shitakiri and oyster.We have determined the criterion level of dehydrogenase activity in fresh shell-fish. The criterion level using the dehydrogenase activity is 144μg/g (mean-2sd) in Akagai, 117μg/g (mean-sd) in Sakiaka, 83μg/g (mean--2sd) in Aoyagi, 90μg/g (mean-sd) in Shitakiri, 611μg/g (mean-2sd) in oyster with shell, and 447μg/g (mean-sd) in shelled oyster, respectively. The dehydrogenase activity in fresh shell-fish is higher than this criterion level.