NON-STARCHY POLYSACCHARIDES OF CEREAL GRAINS: VI. PRELIMINARY STUDY OF THE ENZYMOLYSIS OF BARLEY β-GLUCOSAN

Abstract

Ungerminated barley contains a system of enzymes capable of degrading β-glucosan to glucose, the stages involved including: (a) endo-β-glucosanase action, causing sharp decrease in solution viscosity without any large development of reducing groups; (b) exo-β-glucosanase action, liberating substantial amounts of glucose and, apparently, minor amounts of cellobiose; (c) cellobiase action. Whether glucose is formed solely by hydrolysis of cellobiose, or whether it is also formed directly from β-glucosan and its high-molecular degradation products, remains uncertain. A sample of rye grains contained a similar system of three-fold activity, but one of wheat showed little exo-β-glucosanase. Oats, which had a strong endo-activity, was deficient in exo-activity and in cellobiase. Maize had moderate endo-β-glucosanase activity, but was virtually devoid of exo-activity and of cellobiase. Since barley autolysis is known to result in the dissolution of previously insoluble hemicellulosic β-glucosan, a complete mechanism is available in this cereal grain for conversion of glucosan hemicellulose to glucose, a change of considerable potential importance in malting. The possibility of transglucosidation is not excluded, and it is shown that enzymolysis of cellobiose may be accompanied by synthesis. The relationship of the β-glucosanase system to cellulase and to lichenase is discussed, the structures of β-glucosan and of lichenin now being known to have much in common.