A RAPID SEMIAUTOMATED METHOD FOR THE DETERMINATION OF TOTAL AND WATER-EXTRACTABLE PENTOSANS IN WHEAT FLOURS

A rapid, semi-automated method for the determination of total and wate r-extractable pentosans in wheat flours is described. Total pentosans are solubilized by hot dilute acid within 10 min and water-extractable pentosans by aqueous treatment within 15 min. The solubilization/extr action steps have been optimized with respect to accuracy (weighing of large amounts of sample). rapidity and yield of pentosans. The extrac ts are analyzed for pentose content by an automated adaptation of the phloroglucinol method of Douglas, on a continuous flow analyzer. The c ircuit allows the continuous generation of unstable phloroglucinol/aci d reagent. The rate of analysis has been fixed at 40 samples h(-1). Th e pentosan content of 15 flour samples (total and water-extractable pe ntosans, in duplicate extractions), that is, 60 colorimetric determina tions, may be carried out in one day by a single trained operator. The method is rapid, sensitive and reproducible (CV% < 3) and correlates well with other methods of pentosan determination. No interference has been found from the major components of wheat flours (starch, gluten) . On the other hand, the presence of high levels of some sugars, possi bly encountered in cereal-based products, can result in an underestima tion (fructose: sucrose) or an overestimation (uronic acids) of the pe ntosan concentration.