Enzymic Degradation of Cereal Hemicelluloses

The enzymic degradation of barley β-glucan, whether by endo-β-glucanase or by joint endo- and exo-action, is not smooth, but soon reaches a point beyond which are formed decreasing concentrations of “dextrins” of, apparently, substantially constant complexity, this complexity being less in joint action than in endo-action. The composition of barley β-glucan appears to be best explained on the assumption that the β-l,3- and β-1,4-linkages are each present in small groups (of from I to at least 4), with these groups randomly disposed through the molecule; the differing susceptibilities of different linkages to enzymic attack would depend on the position of these linkages within the groups. Oat β-glucan, on the other hand, is smoothly degraded; although the general molecular plan may be similar to that of the barley product, it would appear that single β-1,3-linkages may be absent or few in number.