Improvement of Ileal Digestibility of DM and Gross Energy By Commercial Carbohydrases Is Associated with Depression of Fermentability in an in Vitro Digestibility Determination System

Efficacy of 11 commerical carbohydrases added to wheat middlings (WM) and corn distillers dried grains with solubles (cDDGS) samples was evaluated using an in vitro enzymatic digestion system coupled with gas production analysis. For in vitro enzymatic digestion, prepared carbohydrase and phytase (Quantum Blue 5 G) solutions were added to WM and cDDGS samples at 20 times of the recommended doses before gastric hydrolysis (2 h, pH = 2.0 with 4mL, 100 mg/mL pepsin solution). Small intestinal hydrolysis occurred for 4 h at pH 6.8 in a phosphate buffer with prepared pancreatin solution (4mL, 100 mg/mL). After enzymatic digestion, the hydrolyzed residues were filtered, dried, and pooled within treatment for subsequent in vitro inocubation in a buffered mineral solution with pig feces inoculum. The enzymatic digestion and fermentation procedures were repeated 16 and 8 times for each treatments, respectively. Gas production was measured for 72 h and kinetics were estimated by fitting data in an exponential model. Fermentation residues were filtered and the supernatant was analyzed for VFA concentrations. Carbohydrases increased (P < 0.05) in vitro ileal digestibility of DM and gross energy in WM by 3.2% and 4.2%, respectively, but not in cDDGS. The concentrations of glucose (73.2 vs. 54.1 mg/dL) and soluble protein (1.27 vs. 1.10 mg/mL) released during hydrolysis were increased (P < 0.05) by the addition of several sources of carbohydrases to WM compared with the non-enzyme treated control. Gas production (262 vs. 365 mL/g DM) was less (P < 0.05) and required more (P < 0.05) time (6.3 vs. 4.8 h) to reach half assyntote T/2^-1 in the hydrolysis residue from WM treated with carbohydrases compared to WM control. For cDDGS, the total gas production (358 vs. 416 mL/g DM) decreased (P < 0.05) and T/2^-1 (13.9 vs. 17.6 h) increased (P < 0.05) when several carbohydrase sources were added compared with the control. The WM control had greater disappearance of DM (45.1 vs. 49.8%) during fermentation than WM supplemented 5 out 11 carbohydrases, whereas there were no differences observed among cDDGS with or without carbohydrases. These results suggest that exogenous carbohydrases increase in vitro ileal digestibility of DM and GE in WM, but decrease fermentation in both WM and cDDGS. This implies that fiber structure may be modified by carbohydrases supplementation in small intestine and may become more resistant to bacteria fermentation in hindgut.