Degradation of dietary fiber by faecal bacteria and potential physiological effects.

摘要

Dietary fiber was extracted from Nigerian ‘gari’, Ex Mannihot esculenta ; plantain, Musa paradisiaca ; Gnetum africana and Telfaria occidentalis and these fiber sources were referred to as GAF, PLF, GF and TF, respectively. Mannihot esculenta and Musa paradisiaca are rich sources of carbohydrate and the fiber extraction was done using termamyl 120L and amyloglucosidase. Gnetum africana and Telfaria occidentalis are vegetables and the acetone dried powder method was employed for fiber extraction. The fiber extracted from each source was subjected to degradation by the gut microbial flora and the extent of degradation after 72 h was determined. Water holding capacity (WHC) of each fiber was measured before and after the degradation. The short chain fatty acids (SCFA) produced during degradation were measured chromatographically. Exposure of the fibers to the gut microflora showed that the non-vegetable fibers (GAF, PLF) were more readily degraded than the vegetable fibers (GF and TF). Consequently, the percentage of the undegraded fiber after 72 h of incubation was highest with the vegetable fibers; GF, 80.0 % and TF, 83.3 %, while that of the non-vegetable fibers (GAF and PLF) was 62.0 % and 72.5 %, respectively. The degradation by the microflora affected the WHC of the fibers (except TF). Water holding capacity (WHC) for GF was 11.1 ± 3.3 g H2O / g fiber, before degradation and 6.3 ± 2.5 g H2O / g fiber after degradation, indicating a percent decrease of about 43.2%. Similar decrease was observed for GAF (30.4 %) and PLF (13.9 %). Only acetic and butyric acid were detected in the fermenting slurry. The relative composition of acetic acid from each of the fiber source (GAF, 62.0 %; PLF, 70.4%; GF, 62.5%; TF, 52.9%) was found to be greater than that from the slurry (control) (42%). The low pH created by the actions of the microflora in the caecal lumen will decrease the toxicity of luminal contents to the gut mucosa and protect against cancer of the colon