I found only 64% pentosan when I performed sulphuric acid hydrolysis on the product rye flour arabinoxylan (P-RAXY). Some sugars may have been destroyed in the hydrolysis. Have you anlaysed the sugar composition of your product?

Yes, we have analysed the product.  It is about 95% arabinoxylan.  The main impurities are ash and protein (plus a few percent water).  Your low value with acid hydrolysis is undoubtedly due to the conversion of the pentose sugars to furfural during the acid hydrolysis.  This is a problem with acid hydrolysis of these types of polysaccharides.

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