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Ammonium sulphate fractionation of barley extracts prepared under conditions which obviate enzyme action allows the preparation of a laevorotatory glucosan uncontaminated by pentosan and of a number of pentosan-rich fractions (contaminated by glucosan). The properties of the pentosan materials are consistent with their being mixtures of xylan, araboxylan and araban each at varying degrees of molecular complexity and of solubility. Malting leads to the substantial elimination of the laevorotatory glucosan, but increases somewhat the recoverable yields of high-molecular pentosan, increase being particularly marked with arabinose-based units. The enzymic changes involved in malting lead to a decrease in viscosity of aqueous solutions of the gums, to increased water solubility, and to a conversion of the isolated gums from a fibrous to a pulverulent condition. Both barley and malt contain galactan, but mannan has been detected in barley only.
Preece et al. (Wed,) studied this question.