The Enzymology of Cell Wall Breakdown During Malting and Mashing: An Overview

Abstract

Enzymolysis of the cell walls of the starchy endosperm of barley can be considered a two-stage process: solubilization and polymer digestion. Solubilase enzymes include not only carboxypeptidase acting as an esterase, but also other enzymes, notably an early-developing xylanase. It is supposed that pentosan is primarily located on the outside of the cell wall. Nonetheless, pentosan is less efficiently degraded than beta-glucan, probably because the chief xylanases are blocked by an endogenous inhibitor. Although there can be very efficient depolymerization of beta-glucan, it appears that degradation is incomplete and that the primary hydrolysis products are beta-linked oligosaccharides. This is likely because the exo-glucanases that hydrolyze them develop late in germination and also have a very low affinity for their substrates. The advantage of this for the brewer is that beer can be legitimately claimed as a good source of putative prebiotics.