In vitro digestibility of dietary protein sources for white shrimp (Penaeus vannamei)

In vitro methods to evaluate protein digestibility are rapid and allow close observation of the peptide bonds cleaved while using only small amounts of raw materials. The pH-stat assay using an enzyme preparation from shrimp hepatopancreas, recently developed by us was used to evaluate the degree of hydrolysis (DH) and estimated protein quality in menhaden, anchovy, white fish, tuna waste, soybean protein, and langostilla meals at 23, 25, and 27°C. Data were obtained by the pH-stat method and were compared with those obtained by the pH-drop method and in vivo assays. The arginine content of the meals was compared with shrimp growth and DH by the pH-stat method. The test showed no significant differences between DH obtained at 23, 25, and 27°C. The pH-stat method predicted protein digestibility better than the pH-drop method. A significant correlation between DH and apparent protein digestibility (APD) was observed. Although a significant correlation between the pH-drop method and APD was observed, the value was low. Arginine showed a significant correlation with shrimp growth but not with APD. The relationship between DH by pH-stat at 25 and 27°C and growth, although significant, had a low correlation. The equations obtained from DH had a very high predictive ability. The standard error in percentage was low. The pH-stat assay has a potential for the estimation of growth and digestibility of shrimp feed.