Oligo-L-methionine and resistant protein promote cecal butyrate productionin rats fed resistant starch and fructooligosaccharide

We examined the role of resistant protein and peptides in promoting cecal b utyrate production in rats fed rapidly fermentable carbohydrates. Rats were fed diets containing raw potato starch (RPS, 200 g/kg diet) or fructooligo saccharide (FOS, 60 g/kg diet) with casein, soy or rice protein (250 g/kg d iet) for 13 d. In rats fed RPS with casein, the major cecal organic acid wa s acetate (441 mu mol), but lactate and succinate were also found in consid erable amounts (324 mu mol). Succinate was the major cecal organic acid (23 5 mu mol) in rats fed FOS with casein. When rice protein was fed with RPS, the contribution of lactate was significantly lower and that of propionate tended to be higher (P < 0.1) than in rats fed casein. In rats fed rice pro tein with FOS, cecal butyrate and acetate were greater and cecal succinate was lower than in rats fed casein with FOS (P < 0.05). Despite the similar amounts of undigested protein in rice and soy proteins, soy protein did not similarly affect cecal butyrate in rats fed FOS or RPS. In another experim ent, rats were fed diets containing high amylose cornstarch (HAS, 200 g/kg diet) with casein, casein + oligo-L-methionine (OM, 3 g/kg diet),soy protei n, soy protein + OM (3 g/kg diet) or rice protein (250 g/kg diet) for 10 d. OM (digestibility, 31 %) was substituted for the same amount of casein. Ra ts fed rice protein had greater cecal butyrate than rats fed casein (P < 0. 05). OM supplementation to casein or soy protein increased cecal butyrate c ompared with rats fed casein or soy protein alone (P < 0.05). These data su pport our hypothesis that resistant protein and peptides promote cecal buty rate production and suggest that the differing potency of rice and soy prot eins in promoting cecal butyrate production might be explained in part by t he different amino acid composition of resistant protein.