EFFECTS OF TEMPERATURE AND pH ON THE ACTIVITIES OF DIGESTIVE ENZYMES IN APOSTICHOPUS JAPONICUS

Activities of digestive enzyme reflect the digestive level of Apostichopus japonicus to different nutritional ingredients. Any changes in ambient factors would affect the activity of a digestive enzyme. Studying different ambient factors on the digestive enzymes in the A. japonicus is important for understanding the behavior of the enzymes. Among ambient factors,temperature and pH are the most two important affecting factors. Enzyme activities were analyzed including protease,lipase,amylase,and cellulase by Folin-phenol method,turbidimetric method,and colorimetric assay of salicylic acid. The results showed that temperature and pH had notable effects on the activities of digestive enzymes in foregut and midgut of Apostichopus japonicus(P 0.05) . The optimum temperature of protease,lipase,and cellulase was 50 ℃,40 ℃ and 40 ℃ respectively in both foregut and midgut,while the optimum temperature of amylase was 40 ℃ in foregut and 30 ℃ in midgut. The protease activity in foregut was higher than that of midgut in an acidic condition at pH 5.0-5.8,while in an alkalescence condition at pH 7.0-8.6,the protease activity was higher in midgut than that in foregut. The lipase activity of foregut was high and stable in two pH ranges:4.2-5.0 and 6.2-7.0,and that of midgut was high at pH 3.8,while the lipase lost enzyme activity at pH over 9.0. The amylase activity was high and stable at pH 6.6-7.4 in both foregut and midgut. The cellulase activity of foregut and midgut was high and stable at pH 6.2-7.4 and 5.4-7.0 respectively. Therefore,the protease activity was the highest among all digestive enzymes,followed by cellulase and amylase activities,and the lipase activity was the lowest.