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 in testinal bacteria of dogs to ferment native and extruded cereal grains and potato starch and cereal grain and potato flours. Substrates included barle y, corn, potato, rice, sorghum, and wheat. In addition to testing native gr ains and flours, extruded substrates also were tested. Substrates were extr uded at low temperatures (LT; 79 to 93 degreesC) and high temperatures (HT; 124 to 140 degreesC) using a Wenger extruder (model TX-52). Substrates var ied widely in concentrations of rapidly digestible starch (RDS), slowly dig estible starch (SDS), resistant starch (RS), and total starch (TS). Extrusi on of most substrates at HT vs LT resulted in increased RDS and decreased R S concentrations. Organic matter disappearance (OMD) values attributed to m icrobial fermentation for a 5-h period were as high as 27% for native extru ded substrates (LT potato starch) and 39% for potato flour. Average OMD was higher for cereal and potato flours than for native extruded substrates (2 9.9 vs 25.4%). Average molar percentages of short-chain fatty acids produce d from all substrates fermented for 5 h were 73, 14, and 13% (acetate, prop ionate, and butyrate, respectively). Average lactate production for substra tes ranked as follows: flours > native and extruded cereal grains and potat o starch (0.33 and 0.18 mmol/g OM, respectively). In vitro microbial fermen tation of starches by ileal bacteria can be substantial and is affected by differences in starch source, fraction, and processed form.