ENZYMIC DEGRADATION OF CEREAL HEMICELLULOSES. I. OBSERVATIONS ON THE β-GLUGOSANASE SYSTEM AND ITS DEVELOPMENT DURING MALTING

Abstract

An initial linear relationship between increases in reciprocal specific viscosity and in reducing group liberation has been confirmed for that aspect of β-glucosanase activity which involves attack on β-glucosan only at points remote from the ends of molecules, i.e., endo-β-glucosanase activity; excess reducing groups over and above those calculated from this relation are ascribed to exo-β-glucosanase and cellobiase, Prolonged endo-action gives progressive degradation of large molecules with ultimate production of cellobiose and laminaribiose; exo-action gives cellobiose 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, endo-activity 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.