Arabinoxylans enzymic hydrolysis

Goldsehmid and Perlin have isolated, by enzymic hydrolysis of an arabinoxylan from wheat flour, a tetrasaccharide which was shown to be 0-a-L-arabinofuranosyl-(l—>3)-0-[i3-D-xylopyranosyl-(l— )]-0- 8-D-xylopy-ranosyl-(1 4)-D-xylose. The L-arabinofuranose side-chains in this polysaccharide are thus present in the a-L configuration, in agreement with the above evidence. 

Synergism between a-arabinosidase, xylanase and j8-xylosidase has been demonstrated in the hydrolysis of wheat straw arabinoxylan with purified enzymes of T, reesei (71). > en only xylanase and )8-xylosidase were used in the hydrolysis, the xylose yield was only 66% of that produced by the whole culture filtrate at the same activity levels of these two enzymes, and no arabinose was produced. Addition of a-arabinosidase increased the yields of both xylose and arabinose. Enhanced hydrolytic action of hemicellulolytic or pectinolytic enzymes in the hydrolysis of alfalfa cell wall polymers by addition of Ruminococcus albus a-arabinosidase has also been reported (37). 

In its attack on L-arabinan, the A. niger enzyme10,85 was found to hydrolyze the substrate rapidly to the extent of 30% thereafter, attack was slow. This initial, rapid hydrolysis of L-arabinan corresponds to the favored attack on the a-L-(l — 3)-linked L-arabinofuranosyl residues, leaving a mainly linear (1 — 5)-a-L-arabinan which was slowly, and eventually, completely, hydrolyzed to L-arabinose. Tagawa and Kaji64 utilized this unique property of their enzyme preparation to prepare from the parent L-arabinan a linear (1 — 5)-L-arabinan which was subsequently purified and characterized. In a similar way, wheat arabinoxylan yielded a predominantly linear (1 — 4)-/3-D-xylan. 

Dietary fibers represent a gronp of carbohydrates, isolable from different plant sources, that are resistant to hydrolysis by enzymes of the gastrointestinal tract. They are divided into two groups water soluble fibers, among which the main are the p-glncans and arabinoxylans, and water insoluble fibers, which include lignins, celluloses, and hemicelluloses. 

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