A Simple Model for the Cell Wall of the Starchy Endosperm in Barley*

Abstract

The solubility of β-glucan in raw barley is substantially reduced if the barley is dehusked with the aid of sulphuric acid and particularly if the grain is denatured by boiling in ethanol. This suggests that endogenous enzymes, which are capable of solubilizing glucan, are present in the grain. However, the release of glucan is greatly enhanced if exogenous enzymes are added. Xylanases are capable of solubilizing glucan, which indicates that the extractability of glucan is limited by arabinoxylan. This is further supported by the observation that arabinofuranosidase, xyloacetylesterase and feruloyl esterase are all capable of effecting some release of glucan. When the fungus Trichoderma viride grows on the denatured barley substrate, the organism secretes xylanase, carboxypeptidase, esterase and arabinofuranosidase before it releases β-glucanase, which further supports the contention that pentosan is encountered before glucan. The evidence is combined into a simple model that indicates that a proportion of the pentosan is on the surface of the wall in the starchy endosperm of barley, where it impedes access to the glucan.