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 (contami nated 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 highmolecular 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.

Using water‐soluble araboxylan of rye as substrate, it is shown that enzymic degradation involves four enzymes or enzyme systems: (a) arabinosidase, liberating free arabinose from araboxylan and from oligosaccharides; (b) endoxylanase, degrading xylan chains, whether or not these carry arabinose side chains; (c) exoxylanase, producing xylobiose from araboxylan and from oligosaccharides after some degree of arabinose removal has been achieved; and (d) xylobiase, liberating free xylose from xylobiose and, perhaps, also from xylotriose. The first detectable low‐molecular product of the joint action of these enzymes is arabinose; xylobiose and xylose appear in detectable quantities somewhat later, and higher oligosaccharides later still. Oligosaccharides with back‐bone chains of up to six xylose residues have been observed, these carrying varying proportions of arabinose residues in side chains. Different raw cereals carry all four enzyme systems, but in different proportions; the malting enhancement of pentosanase activity in barley is small compared with the enhancement of β‐glucanase activity.

An initial linear relationship between increases in reciprocal specific viscosity and in reducing group liberation has been confirmed for that aspect of /?-glucosanase activity which involves attack on /3-glucosan only at points remote from the ends of molecules, i.e., endo-/?-glucosanase activity; excess reducing groups over and above those calculated from this relation are ascribed to exo-/?-glucosanase and cellobiase, Prolonged endo-action gives progressive degradation of large molecules with ulti mate production of cellobiose and laminarlbiose; exo-action gives celloblose from the start. The presence of cellobiase makes glucose production inevitable. Different raw cereals show different proportions of endo-and exo-activity and of cellobiase, but barley is moderately rich in all three. During the malting of barley, endoactivity is enhanced 100-200 fold, and there is a measure of resistance to heat inactivation on the kiln. Available evidence suggests that the increase in exo-activity is only moderate, and this activity may be entirely suppressed by kilning. Cellobiase activity is variable, but has been found in all extracts and preparations examined.Methods for differential inactivation of endo-and exo-enzymes have been examined, but only the latter can be readily destroyed. Vol. 62, 1056] PREECE AND HOGGAN: /J-GLUCOSANASE SYSTEM OF CEREALS 487

Using the principle of ammonium sulphate fractionation successfully applied earlier to prepare β‐glucosan from barley, a similar product has now been obtained from oats, whilst a pentosan fraction free from hexosan has been obtained from rye; the nature of the araban‐xylan association is discussed. In respect of water‐soluble gum content and composition, mature grains of the five cereals rye, wheat, barley, oats and maize form a series, the characters of which are not unrelated to the taxonomic positions of these cereals. Rye is rich in water‐soluble pentosan, but in wheat there is greater contamination of the abundant pentosan by glucosan, mainly apparently of dextrinous type. β‐glucosan is the principal gum of both barley and oats, but the amount of pentosan in barley gum is considerably greater than in that from oats. Maize contains little water‐soluble' material of gum‐like nature and the principal water‐soluble polysaccharide is dextrinous. All five cereals contain material, non‐precipitable by ammonium sulphate, which yields glucose, xylose, arabinose and galactose on hydrolysis.

Comparative studies of the gross yields of unfractionated water-soluble gum-like materials from a number of cereals indicate that barley Is probably the best source of laevorotatory glucosan and rye the best source of pentosan; wheat occupies an intermediate position, but oats and maize are poor sources of pentosan. In the case of some raw materials, and of adjuncts whose manufacture has involved heat or mechanical treatment, the gum-like materials are strongly contaminated with water-