Effect of feed diet on aminopeptidase activities from the hepatopancreas of white shrimp (Penaeus vannamei)

White shrimp (Penaeus vannamei) were fed one of seven diets for 30 days. Diets contained 85% of a reference ration and 15% of either anchovy, tuna waste meal, deboned fish meal, langostilla crab meal, soybean meal, menhaden meal A, or menhaden B as a protein replacer. At the end of the feeding trial, animals were sacrificed and 10 aminopeptidase activities of the hepatopancreas tissue were assayed. The hepatopancreas tissues contained Arg-, Leu-, His-, Ile-, Lys-, Met-, Thr- and Val-aminopeptidase activities but no activity was detected for Phe-aminopeptidase. Leu-aminopeptidase activity was inhibited by Zn(+2) and Mg(+2) salts and activity was also inhibited when more than a 0.2 mg hepatopancreas extract protein was included in the assay. Principal component analysis was used to determine whether diet had an influence on hepatopancreas aminopeptidase activities. The aminopeptidase activities were greater for animals fed a diet containing menhaden fish meal B. This was principally the result of the higher levels of Met-, Val-, Pro-, Lys-, and Leu-aminopeptidase activities in animals fed menhaden fish meal. Menhaden fish meal B had a lower nutritional quality for shrimp than the other protein replacers. Seven of the 10 essential amino acids for shrimp were present at less than 100% of the recommended values. On the other hand, shrimp fed soybean meal replacer contained lower amounts of aminopeptidase activity, notably Gly- and Met-aminopeptidase activities, and the meal was of excellent quality having only one limiting amino acid. The results indicate that the shrimp diet can influence proteolytic activity of the hepatopancreas tissue. This is significant to the seafood technologist since previous studies showed that hepatopancreas proteases can leach into the meat postmortem and cause tissue softening.