Effects of citric acid, alpha-galactosidase and protease inclusion on in vitro nutrient release from soybean meal and trypsin inhibitor content in raw whole soybeans

An experiment was conducted to evaluate the effects of citric acid (CA) and commercial preparations of α-galactosidase (α-GAL) and protease on in vitro nutrient release from soybean meal (SBM) and trypsin inhibitor (TI) content in raw defatted whole soybeans. An in vitro model was used to simulate the chickenʹs digestive process in the crop, the stomach (proventriculus and gizzard) and the small intestine. Soybean meal and ground whole soybeans were used as substrates. Graded levels of either α-GAL (0–13,792 units/kg) or protease (0–888 units/kg) and 0 or 20 g CA per kg were added to the substrates in a factorial arrangement. Reducing sugars (RS) and α-amino N were measured at the end of the crop phase, the stomach phase, and the whole phase (crop through small intestine). Trypsin inhibitor content was measured at the end of the stomach phase. Increasing α-GAL levels linearly (P<0.01) increased the release of RS in both the crop and the whole phases. Addition of CA with α-GAL further increased enzyme activity, resulting in a significant interaction (P<0.01). Linear increases (P<0.05) in α-amino N occurred with increasing doses of protease at the crop, the stomach and the whole phases. Inclusion of CA in the incubation mixture also increased (P<0.05) α-amino N at all three phases. An interactive effect (P<0.01) between protease and CA was observed only in the crop phase. Neither protease nor CA had an effect on TI activity in raw soybeans. The results suggest that α-GAL and protease may be useful in hydrolyzing the carbohydrates and proteins, respectively, in SBM and the effects of these two enzymes may be enhanced by acidifying the diet.