pH-stat method to predict protein digestibility in white shrimp (Penaeus vannamei)

In aquaculture, feeding trials are the most dependable method of measuring nutritive value of feeds. However, these methods are time consuming, expensive, and the results may be affected by environmental factors. In vitro methods to evaluate protein digestibility are rapid and allow close observation of how far bonds are cleaved using only small amounts of raw materials. We developed a pH-stat assay using an enzyme fraction from shrimp hepatopancreas. We used the assay to evaluate the degree of hydrolysis (DH) and estimate protein quality in menhaden, anchovy, white fish, tuna waste, soybean protein, and langostilla meals. Data obtained by the pH-stat method were compared with those obtained by chemical analysis and an in vivo apparent protein digestibility (APD) assay. The pH-stat method predicted the protein quality better than chemical analysis. The APD of the experimental diets ranged from 64-91%. A significant correlation (P < 0.05) between DH and APD was observed (r² = 0.77 for enzymes from shrimp hepatopancreas and r²= 0.71 for a commercial enzyme mixture). The pH-stat method has the potential for estimating the digestibility of alternative protein sources for shrimp feeds.