A study of the effects of dietary gum arabic in the rat

Gum arabic (GA) is a water-soluble polysaccharide (molecular weight approximately 850 000) containing rhamnose, arabinose, glucuronic acid and galactose. The metabolism of GA has been studied in the rat. Adult male Wistar rats were given GA incorporated into either an Oxoid breeders (OB) diet or an elemental (Elem) diet. Intestinal contents were examined for precipitable GA using acidified ethanol. GA was found from stomach to small intestine but not in the caecum, colon or rectum. Caecal excision and restoration of intestinal continuity resulted in GA recovery from stomach to rectum. Excreted methane, hydrogen and volatile fatty acids (VFA) were measured as indicators of bacterial activity in the caecum and colon. Methane excretion increased on the OB + GA diet and H2 concentrations remained unaltered. The Elem diet abolished gas production. When the animals were given the Elem + GA diet, H2 and methane were only produced after 28 d. Faecal VFA increased with increasing GA intake, acetate concentration increased and butyrate concentration decreased with increasing GA dosage. Significant decreases in concentrations of VFA were found from caecum to left colon and from left colon to faeces. It can be concluded that GA degradation occurs in the caecum and is associated with increased methane excretion, increased VFA concentrations and changes in the proportions of various VFA in the faeces.