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

Legumes are a popular grain-free alternative carbohydrate source in canine diets, however, information on their fermentative characteristics have not been established. Thus, the objectives of the present study were to 1) quantify the chemical compositions and 2) fermentative profile of select legumes using canine fecal inoculum. Five legume varieties, whole yellow peas (WYP), green lentils (GL), black bean grits (BBG), navy bean powder (NBP), and garbanzo beans, were analyzed and compared to a positive control, beet pulp (BP). Substrates were analyzed for gross energy (GE), dry and organic matter, crude protein (CP), acid hydrolyzed fat, and total dietary fiber (TDF) fractions, beta-glucans, starch-free, and hydrolyzed sugars, as well as fermentative characteristics: pH, short-chain fatty acids (SCFA), branched-chain fatty acids (BCFA), total gas, hydrogen, and methane. Substrates then underwent a two-stage in vitro digestion and subsequent fermentation using canine fecal inoculum for 0, 3, 6, 9, and 12 h. All test substrates contained approximately 8% to 9% moisture and 4.5 kcal/g GE. The highest CP content was observed in GL (27%). Analyzed TDF content of test substrates was greatest for WYP (32%) and GL (36%). Total starch content was greatest for GL (58%) and WYP (56%). Sucrose and stachyose were the most predominant free sugars and glucose was the most predominant hydrolyzed sugar among test substrates. After 3 and 6 h of fermentation, a net negative change in pH was observed among most substrates with a net negative change in all substrates after 9 and 12 h. Values for SCFA did not differ among substrates after 3 or 6 h of fermentation with BP and WYP among the greatest acetate (1,656 and 1,765 umol/g, respectively) and propionate production values (157.7 and 126.1, respectively) after 9 h. All substrates produced greater total gas volumes than WYP after 3 h, with no differences observed after any other time points. However, BP hydrogen production values were greater after 9 and 12 h (P < 0.0001; 726,042 and 394,675 ng/g, respectively) with greater methane production values after 12 h (P < 0.0001; 54,291 ng/g) than all test substrates. These data suggest that legumes offer a diverse macronutrient profile and appear to be a source of slowly fermentable fiber, which may have beneficial implications on the ratios of saccharolytic to proteolytic fermentation toward the distal colon.