Ammonia fiber expansion increases in vitro digestibility and fermentability of corn distillers dried grains with solubles with or without carbohydrases

•Ammonia fiber expansion (AFEX) modified corn distiller’s grains with soluble (DDGS) fiber structure.•In vitro digestibility of energy increased by AFEX pretreatment.•Exogenous enzyme addition increased the in vitro digestibility in specific DDGS. A significant portion of gross energy (GE) in corn distillers dried grains with solubles (DDGS) is indigestible by non-ruminants, and the impact of ammonia fiber expansion (AFEX) on improving GE digestibility is unknown. The objective of this study was to determine the effect of AFEX and enzymes on crystallinity index and neutral detergent fiber (aNDF) degradation in DDGS using a porcine in vitro fermentation system. Two sources of DDGS samples (ICM and POET) were pretreated with liquid ammonia at 100 °C and 2069 kPa for 30 min. The DDGS samples with or without AFEX pretreatment were predigested with pepsin and pancreatin with or without carbohydrases (1500 U/g xylanase, 1100 U/g β-glucanase, 110 U/g mannanase, and 35 U/g galactosidase). Residues were then subjected to in vitro fermentation (directly inoculating DDGS samples with fecal inocula) and accumulated gas production recorded up to 72 h. Concentration of short-chain fatty acids (SCFA) were measured in the fermented solution. On a dry matter (DM) basis, non-protein nitrogen was increased by 20.8 g/kg, and aNDF was decreased by 146 g/kg in corn DDGS after AFEX pretreatment. Pretreatment with AFEX decreased the crystallinity index of fiber in DDGS from about 15 to 0 %, increased (P < 0.01) fermentability of DM and aNDF, and decreased (P < 0.01) unfermented aNDF content after in vitro fermentation for 12 and 72 h. The AFEX pretreated DDGS had greater (P < 0.05) in vitro digestibility of DM and GE, greater production of acetic acid and total SCFA (DM enzymatic hydrolyzed residue basis), greater in vitro digested GE (GE × IVDGE, GE) and digestible energy (GE + energy derived from SCFA) compared with DDGS without pretreatment. Carbohydrase supplementation increased (P < 0.05) in vitro digestibility of GE and DM in AFEX treated POET but not in ICM DDGS. In conclusion, AFEX pretreatment decreased the crystallinity index of fiber and improved the in vitro digestibility and fermentability of corn DDGS.