Martin F Chaplin | PubMed Health

PubMed2003

Fibre and water binding.

The range of interactions between fibre and water and the consequential properties of the bound water are modelled and examined. Dietary fibre may interact with water by means of polar and hydrophobic interactions, hydrogen bonding and enclosure. The results of these interactions vary with the flexibility of the fibre surface. When the fibre is insoluble or junction zones are formed,this may result in profound changes in the surrounding water. Such interactions are capable of affecting the structuring and solvation properties of water well away from the immediate surfaces involved. In particular, the specific properties of water enclosed by dietary fibre are examined, an area of investigation previously receiving scant attention. The way this enclosure may affect the properties of water is exemplified by modelling the colon to show how fibre may exert a beneficial action by the preferential partitioning of hydrophobic carcinogens. Unfermented dietary fibre has a tendency to form low-density expanded water that acts as a preferential solvent for hydrophobic molecules when compared with the less-structured denser water within the much more hydrophilic mucus layer.

Colon↗

PubMed2003

Primary structure of arabinoxylans of ispaghula husk and wheat bran.

The primary structures of ispaghula husk and wheat bran were investigated in order to determine how and why these fibres are among the most beneficial dietary fibres. To this end, the polysaccharide preparations have been subjected to enzymic hydrolysis and methylation analysis.The results have shown ispaghula husk and wheat bran to be very-highly-branched arabinoxylans consisting of linear f-D-(1-4)-linked xylopyranose (Xylp) backbones to which a-L-arabinofuranose (AraJ3 units are attached as side residues via a-(l13) and a-(1-02) linkages.Other substituents identified as present in wheat bran include P-D-glucuronic acid attached via the C(O)-2 position, and arabinose oligomers, consisting of two or more arabinofuranosyl residues linked via 1-2, 1-3, and 1-4 linkages. Ispaghula-husk arabinoxylan is more complex having additional side residues which include a-D-glucuronopyranose (GalAp)-(1-42)-linked-a-L-rhamnopyranose-(1-04)-0-D-Xylp, a-D-GalAp-(l-o3)-linked-a-L-Araf-(l-4)-[3-D-Xylp, and a-L-Araf-(l-43)-linked-P-D-Xylp-(1l -4)--D-Xylp. The beneficial effects of increased faecal bulk and water-holding capacity are undoubtedly related to the structures of the arabinoxylans, with differences in their efficacy to treat various functional bowel disorders due to their specific structural features.

Carbohydrate Sequence↗