FEEDING RESISTANT STARCH AFFECTS FECAL AND CECAL MICROFLORA AND SHORT-CHAIN FATTY-ACIDS IN RATS

The effects of different forms of resistant potato starch (RS) on the major microbial population groups and short-chain fatty acids (SCFA) i n the cecum and feces of rats were studied over a 5-mo feeding period. Thirty 8-wk-old male Wistar rats, averaging 210 g initial body weight , were adapted for 7 d to a balanced basal diet containing 60% waxy ma ize starch devoid of any RS. On d 8, three groups of 10 rats each were fed diets containing the following forms of starch: 1) rapidly digest ible waxy maize starch (basal diet), 2) a mixture of 83.3% waxy maize starch and 16.7% native granular potato starch (RS 1), or 3) a mixture of 33.3% waxy maize starch and 66.7% modified potato starch (RS 2). T he final RS content in RS 1 and RS 2 was 10%. Fecal samples were colle cted at d 8 and 1, 3, and 5 mo after the start of the experiment. Ceca l contents were taken after 5 mo. The colony counts of microbial group s did not vary with time in the control or the RS 1 group (P > .05). O nly the number of Bacteroides/fusobacteria decreased between mo 1 and 5 in rats fed RS 1 (P < .05). The RS 2 diet led to a significant incre ase in total culturable bacteria, lactobacilli, streptococci, and ente robacteria between mo 1 and 5. The RS 1 and RS 2 diets stimulated the growth of bifidobacteria. Cecal numbers of lactobacilli, streptococci, and enterobacteria were higher in rats fed RS 2 than in rats fed RS 1 or control diet (P < .05). Lactobacillus cellobiosus occurred only in rats fed RS 1 or RS 2. Acetate increased in mo 3 compared with d 8 in all groups (P < .05). The fecal and cecal SCFA displayed higher conce ntrations of acetate and propionate and a higher molar proportion of p ropionate in RS 2 than in RS 1 or control rats (P < .05). Stimulation of bifidobacteria, lactobacilli, and SCFA may be useful for the suppre ssion of pathogenic organisms in the colon.