Effects of Acids and Storage Temperatures on the Phospholipase A Activities in Oyster Digestive Glands.

Abstract

Effects of the acids and storage temperatures on the phospholipase A (PLase A) activities in oyster digestive glands (ODG) were investigated. The results were summarized as follows ; 1) Specific activities of both PLase A1 and A2 in ODG treated with acetic acid and stood at 37°C were higher than those in control group. The increase of these enzyme activities in ODG treated with 4% acetic acid (pH 2.5) was larger than those with 1% and 16% acetic acid. The enhancement of the enzyme activities in ODG was induced within 1 hr after the treatment. 2) No significant change was observed in the specific activities of PLase A1 and A2 in ODG treated with 0.01 N HCl (pH 2.2) and stood at 37°C throughout experimental period (5 h). The values were not different from those in control group. 3) Protein contents in all ODG samples treated with acids were lower than those in control group. The ODG treated with 4% acetic acid at 37°C had the lowest value. 4) Specific activities of both PLase A1 and A2 increased 3 d after the storage at 5°C. The increase of these specific activities observed until 2 weeks after the storage at 5°C was considered to be due to the decrease ofprotein contents. The degree of increase in enzyme specific activity at 3 weeks, however, was proportionally larger than that of the decrease in protein contents. No significant change was observed in PLase A activity in ODG stored at both -20°C and -70°C. 5) The optimum temperatures of PLase A1 and A2 were 37°C. The results showed that an increase of PLase A activity was induced in the early stage of oyster marination stood at 37°C. It was suggested that hydrolysis in phospholipid and protein denaturation would precede the enhancement of PLase A, and temperature could be one of the important factors on the enzyme activation.