EFFECTS OF TEMPERATURE AND pH ON ACTIVITY OF DIGESTIVE ENZYMES IN SHRIMP PENAEUS VANNMEI

Using temperature/pH two-factor cross method,activily of three digestive enzymes in liver,intestine and stomach of shrimp Penaeus vannmei with wet weight of (6.58±0.78)g were examined to find out the best temperature/pH environment. The resuhs showed that when pH value ranges was between 5.2—8.7,the most favorable temperature for the amylase in liver,intestine and stomaeh were 30,35 and 30—35℃ respectively. When temperature range was between 15—40℃,the most favorable pH values were all 6.2. The results indicated also that the amylase was conducive in weak acidic condition. The best temperatures in liver,intestine and stomach for the protease were 50—65℃,55—65℃ and 60℃ respectively when the reacting pH values range was between 4.5—9.0 in liver,intestine protease and 1.5—6.5 in stomach protease,The best pH values for the protease of liver were 8.5—9.0,and of intestine were 7.5—8.5,and of stomach were 2.0 and 5.0—6.5 when the reacting temperature range was 25—65℃. These resuhs indicated that the most favorable temperatures in liver,intestine and stomach for protease were higher than growth temperature of P. vannmei Furthermore,the protease in liver and intestine were conducive to alkaline condition while the protease in stomach was conducive to acidic condition. The activny of lipase was weak and lower than that of protease and amylase. The oplimum temperature in liver,intestine and stomach for the lipase all were 37℃ when the reacting pH values range was between 5.7—8.2,and the optimum pH values all were 7.7 when the reacting temperature range was between 25—45℃. The result indicated that the lipase was conductive to weak alkalinity. The pH values in intestine,liver and stomach of P. vannmei measured in our experiment were 5.9—6.1 (6.08±0.04),6.7—7.0 (6.82±0.04) and 5.1—5.3 (5.22±0.04) respectively. This result indicated that the pH values in digestive organs of P. vannrnei were weak acidic. All the activity of three digestive enlzymes was in an order of from strong to weak:protease,amylase,lipase in liver,intestine and stomach at the most favorable reacting temperature and pH.