In vitro fermentation characteristics of native and processed cereal grains and potato starch using ileal chyme from dogs

Two in vitro experiments were conducted to evaluate the ability of small intestinal bacteria of dogs to ferment native and extruded cereal grains and potato starch and cereal grain and potato flours. Substrates included barley, corn, potato, rice, sorghum and wheat. In addition to testing native grains and flours extruded substrates also were tested. Substrates were extruded at low temperatures (LT; 79 to 93°C) and high temperatures (HT; 124 to 140°C) using a Wenger extruder (model TX-52). Substrates varied widely in concentrations of rapidly digestible starch (RDS), slowly digestible starch (SDS), resistant starch (Rb), and total starch (TS). Extrusion of most substrates at HT vs LT resulted in increased RDS and decreased RS concentrations. Organic matter disappearance (OMD) values attributed to microbial fermentation for a 5-h period were as high as 27% for native extruded substrates (LT potato starch) and 39% for potato flour. Average OMD was higher for cereal and potato flours than for native extruded substrates (29.9 vs 25.4%). Average molar percentages of short-chain fatty acids produced from all substrates fermented for 5 h were 73, 14 and 13% (acetate, propionate, and butyrate, respectively). Average lactate production for substrates ranked as follows: flours > native and extruded cereal grains and potato starch (0.33 and 0.18 mmol/g OM, respectively). In vitro microbial fermentation of starches by ileal bacteria can be substantial and is affected by differences in starch source, fraction, and processed form.