Enzyme pre-treatment of soybean meal: Effects on non-starch carbohydrates, protein, phytic acid, and saponin biotransformation and digestibility in mink (Neovison vison)

The study was conducted to examine if crude enzymes (E) produced from Aspergillus niger by solid state fermentation could bio-transform carbohydrates, proteins, inositol phosphate (InsP) and saponins in soybean meal (SBM) under low moisture conditions. Two experiments were performed to determine the effect of mixing, moisture content, treatment time and E levels during enzyme hydrolysis. 1) A single replicate 2 3 full factorial screening design was used to determine the effect of the independent continuous variables time (30 and 70 min), moisture (350 and 450 g kg −1 DM), and the category variable mixing (i.e. effect of static conditions vs. active mixing (X3, S/M)) during the enzyme hydrolysis. 2) A three factorial central composite design (CCD) was used to study the effects of moisture content (316–484 g kg −1 DM), time of hydrolysis (16.4–83.6 min), and E content (0.32-3.68 g kg −1 SBM dry matter (DM)). The first experiment demonstrated that hydrolysis of InsP 6 was significantly affected by time (P < 0.01), moisture content (P < 0.0001) and static vs. mixing (P < 0.01). The hydrolysis of Bb-DDMP was also significantly affected by static vs. mixing (P < 0.05). The second experiment demonstrated that the hydrolysis of InsP 6 was significantly affected by time (P < 0.001), moisture (P ˂ 0.001) and enzyme content (P ˂ 0.01). The InsP 6 content was reduced 84% after 70 min, at a moisture content of 450 g kg −1 DM with the addition of 3 g enzyme kg −1 SBM DM, the InsP 5 -InsP 3 were not accumulated at these parameter settings. The hydrolysis of the saponin group Bb was explained by the enzyme square regressor (P < 0.001) and the interaction between moisture and enzyme (P < 0.001) reaching a maximum by the addition of 2.5 g enzymes kg −1 SBM DM at 484 g kg −1 moisture content. No significant effects on soluble protein and dietary fiber were observed. Mink were fed three diets containing 50% of the protein from SBM, SBM treated without enzymes or treated with enzymes. There was a trend of improved ash apparent digestibility in mink by the enzyme treatment (P = 0.07), but not for phosphorous. The apparent digestibility of protein and amino acids (AA) in mink was improved by the heat treatment used to inactivate the enzymes (P < 0.001), however, not by the enzyme treatment itself