Short‐chain fatty acid content and pH in caecum of rats fed various sources of starch

Abstract

AbstractCaecal pH and contents of short‐chain fatty acids (SCFA) were registered in rats fed three potential sources of resistant starch (RS); raw pea starch, raw potato starch, and an RS‐enriched preparation obtained from wheat starch by autoclaving and enzymatic incubation. Small intestinal digestibility and delivery of RS to the hind‐gut in the case of raw starches were determined by analysis of faecal starch in animals treated with antibiotics to prevent hind‐gut fermentation. RS content in the RS‐enriched preparation was determined as total starch remaining in an enzymatic gravimetric dietary fibre residue. The fermentability of RS was estimated from the faecal recovery of starch in normal animals with intact hind‐gut microflora. Approximately 35 g per 100 g and 32 g per 100 g were RS in the case of raw potato starch and the RS‐enriched preparation, respectively, versus only 1 g per 100 g in the case of raw pea starch. The caecal pH decreased with all test diets, being most significant with raw potato starch. SCFA production and faecal bulking were negligible with raw pea starch, whereas both raw potato starch and the RS‐enriched preparation significantly increased these parameters. The fermentability of RS in raw potato starch and the RS‐enriched preparation was similar, or about 60–70%. If calculated on basis of fermented amount, RS in raw potato starch was more potent in generating SCFA (49 μmol g−1) than in the RS‐enriched preparation (19 μmol g−1). RS in raw potato starch also displayed the highest faecal bulking capacity. In fact, the faecal dry weight increased more than expected merely from delivery of RS. The relative proportion in caecal contents of acetic‐, propionic‐ and butyric acid was 70, 17 and 8%, respectively, with no significant differences between the three sources of RS.