Changes in composition and structure of wheat bran resulting from the action of human faecal bacteria in vitro.
Cell-wall material of wheat bran was incubated with human faecal bacteria for 24-72 h and the resulting structural changes were studied by methylation analysis. Of the carbohydrate content, approximately 39% was degraded after 24 h, increasing to only 44% after 72 h. Arabinoxylans and mixed-linkage beta-D-glucans from the aleurone layer were degraded preferentially. After treatment of the bran with alkali, the extent of degradation was increased three-fold as a result of saponification of ester cross-links which facilitated increased degradation of the polymers from both the aleurone and outer, lignified, layers. There was evidence that ester linkages between the glucuronosyl residues, attached to O-2 of the (1----4)-linked xylosyl residues, and phenolic groups of lignin were also saponified. The treatment with alkali also rendered the cellulose more susceptible to bacterial attack. The alkali-soluble acidic arabinoxylan fractions of the bran were degraded readily by bacterial action, but the xyloglucans cross-linked to arabinoxylans by phenolics were relatively resistant.
Stevens
B J
BJ
AFRC Food Research Institute, Norwich, Great Britain.
Selvendran
R R
RR
D001089:Arabinose / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D002236:Carbohydrate Conformation; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000032:analysis; D002473:Cell Wall / Q000378:metabolism*; D002482:Cellulose / Q000378:metabolism; D055598:Chemical Phenomena; D002621:Chemistry; D004043:Dietary Fiber / Q000378:metabolism*; D005243:Feces / Q000382:microbiology*; D005936:Glucans / Q000378:metabolism; D006801:Humans; D006878:Hydroxides; D008745:Methylation; D011188:Potassium; D017680:Potassium Compounds; D012995:Solubility; D014908:Triticum; D014994:Xylose / Q000378:metabolism
D002241:Carbohydrates; D004043:Dietary Fiber; D005936:Glucans; D006878:Hydroxides; D017680:Potassium Compounds; D002482:Cellulose; D014994:Xylose; D001089:Arabinose; D011188:Potassium; C029943:potassium hydroxide