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Enzymic modification and measurement of wheat flour arabinoxylan  
B. V. MCCLEARY (1), V. McKie (2), J. Larkin (3), A. Draga (3). (1) Megazyme International Ireland Ltd., Bray, County Wicklow, Ireland; (2) Megazyme International Ireland., Bray, County Wicklow, Ireland; (3) Megazyme International Ireland, Bray, County Wicklow, Ireland

The aim of the current research is to develop an enzymic procedure for the measurement of wheat flour arabinoxylan. 

Method: Hydrolysis of arabinoxylan requires the concerted action of <i>endo</i>-1,4-ß-xylanase (xylanase), α-L-arabinofuranosidase and ß-xylosidase. Xylanases vary significantly in their ability to depolymerise substituted xylan chains and arabinofuranosidases vary in their ability to remove specific arabinofuranosyl residues from the arabinoxylan backbone, so a range of each of these enzymes were produced through recombinant techniques and their ability to cooperatively act in the hydrolysis of arabinoxylan and arabinoxylan-oligosaccharides has been studied. Released arabinose and xylose were measured using galactose dehydrogenase, xylose dehydrogenase and mutarotase.

Results: Xylanase from <i>Cellvibrio mixtus</i> is very effective in depolymerising WAX and ADWAX (acid debranched wheat arabinoxylan), whereas that from <i>Neocallimastix patricarum</i> is severely inhibited by α-L-arabinosyl branches on the arabinoxylan. α-L-Arabinofuranosidases also vary dramatically in their ability to release L-arabinose from arabinoxylan and arabino-xylo-oligosaccharides. Enzymes from <i>Biffidobacter adolescentis</i> and <i>Bacteroides ovatus</i> (BACOVA_03417) can only hydrolyse the 1,3-α-linked L-arabinose from doubly substituted D-xylose residues. In contrast, an enzyme from <i>Ustilago maydis (</i>UmAbf62A) has little or no action on L-arabinosyl groups on doubly substituted D-xylosyl residues, but rapidly hydrolyses single L-arabinosyl residues from the arabinoxylan backbone. These enzymes in combination with <i>Selenomonas ruminantium</i> ß-xylosidase give near complete hydrolysis of soluble wheat arabinoxylan to arabinose and xylose.

Conclusion: The basis if an enzymic procedure for the measurement of soluble wheat flour arabinoxylan has been developed.

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