Hydrolysis of the soluble pentosans of wheat flour and Rhodymenia palmata by ruminal micro-organisms

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Abstract
The hydrolysis of 2 water-soluble pentosans by toluene-treated suspensions of bacteria from sheep rumen has been studied. The pentosan of wheat flour and the xylan of the red seaweed Rhodymenia palmata, for which the trivial name rhodymenan is proposed, are both hydrolyzed to completion by the bacterial suspension under physiological conditions. Hydrolysis of the wheat-flour pentosan by the bacterial suspension proceeds by removal of the arabinose side chains and fragmentation of the main xylose chain simultaneously. Partially hydrolyzed pentosan was fractionated on a charcoal column, yielding arabinose and xylose, xylobiose, xylotriose, xylotetraose and xylopentaose, together with a series of high oligosaccharides. Oligosaccharides of low molecular weight, containing both arabinose and xylose, are present in the hydrolysate only in traces. Rhodymenan, when partially hydrolyzed by the bacterial suspension yields xylose, xylobiose and xylotriose, together with a number of hitherto unknown xylose oligosaccharides. Two of the latter were obtained in crystalline form; one is a disaccharide for which the name rhodymenabiose is proposed and the other is a trisaccharide. An amorphous xylose tetrasaccharide was also isolated. The structure O-[beta]-D-xylopyranosyl-(l[forward arrow]3)-D-xylopyranose is suggested for rhodymenabiose. The structure of the trisaccharide was shown to be O-[beta]-D-xylopyranosyl-(l[forward arrow]3)-O-[beta] D-xylopyranosyl-(l[forward arrow]4)-D-xylopyranose. The sequence of linkages in the tetrasaccharide is either [beta]-1:4, [beta]-1:3, [beta]-1:4 or, less probably, [beta]-1:3, [beta]-1:4, [beta]-1:4. The structure of rhodymenan is discussed in the light of these findings.