Chemical composition and in vitro fermentation characteristics of ancient grains using canine fecal inoculum

Human interest in ancient grains replacing traditional carbohydrate sources has reached the pet food market; however, chemical composition of these grains and their digestive properties in the canine model, specifically the fermentative characteristics, have not been established. Five ancient grain varieties were analyzed: amaranth (AM), white proso millet (WPM), oat groats (OG), quinoa (QU), and red millet (RM). Cellulose (CEL) was used as a negative control, and beet pulp (BP) was used as a positive control. Substrates were analyzed for macronutrient composition as well as free and hydrolyzed sugar profiles in addition to their in vitro fermentative characteristics. Substrates were allocated into 2 sets to allow for quantification of pH, short-chain fatty acids, and branched-chain fatty acids, as well as gas volume and composition. Samples were digested for 6 and 18 h with pepsin and pancreatin, respectively, prior to inoculation with fecal bacteria for 0, 3, 6, 9, or 12 h. Detectable levels of cereal β-glucans were observed solely in OG (3.5%), with all other substrate containing <0.35% cereal β-glucans. All test substrates had fairly similar macronutrient and starch profiles with the exception of RM that contained the highest resistant starch content (2.4%), with all other test substrates containing <0.5% resistant starch. However, the analyzed pseudocereals, AM and QU, had the highest concentrations of free glucose while the minor cereal grains, WPM, OG, and RM, contained the highest concentrations of hydrolyzed glucose. All test substrates had propionate production values similar or greater than BP after 3, 6, 9, and 12 h of fermentation, and similar or greater butyrate production values than BP after 6, 9, and 12 h. All substrates had greater (P < 0.05) changes in pH than CEL after 6, 9, and 12 h, with AM, WPM, OG, and RM having greater (P < 0.05) changes in pH than BP after 9 and 12 h. These data suggest select ancient grains have similar fermentation characteristics as BP, a moderately fermentable fiber considered the gold standard in terms of fiber sources in the pet food market today, and that OG and AM may be more fermentable during longer fermentation periods.