Cell wall polysaccharides hydrolysis of malting barley (Hordeum vulgare L.): a review

Malting quality results from the different steps of the malting process. Malting uses internal changes of the seed occurring during germination, such as enzymes synthesis, to obtain a good hydrolysis process and the components required. Among the three main hydrolytic events observed, that are namely starch degradation, cell wall breakdown and protein hydrolysis, an efficient cell wall polysaccharides hydrolysis is an essential condition for a final product of quality. Indeed, because of the physical barrier of the cell wall, cell wall polysaccharides hydrolysis is one of the first steps expected from the process to gain access to the cell components. Moreover, viscosity problem and haze formation in malting industry are related to their presence during the process when inefficient degradation occurs, leading to increased production time and cost. Understanding the key elements in cell wall degradation is important for a better control. (1-3,1-4)-beta-glucans and arabinoxylans are the main constituents of cell wall. (1-3,1-4)-beta-glucans are unbranched chains of beta-D-glucopyranose residues with beta-(1,3) linkages and beta-(1,4) linkages. Arabinoxylan consists in a backbone of D-xylanopyranosyl units linked by beta-(1-4) bonds connected to single L-arabinofuranose by alpha-(1 -> 2) or alpha-(1 -> 3)-linkages. Degradation of (1-3,1-4)-beta-glucans is processed by the (1-3,1-4)-beta-glucanases, the beta-glucosidases and the beta-glucane exohydrolases. It seems that the (1-3)-beta-glucanases are also involved. Arabinoxylans are mainly decomposed by (1-4)-beta-xylan endohydrolase, arabinofuranosidase and beta-xylosidase.