Oat endosperm cell walls. II. Hot-water solubilization and enzymatic digestion of the wall

Isolated cell walls from two cultivars of oats, one with a high content of β-glucan (Marion) and one with a low β-glucan content (OA516-2), were fractionated in an attempt to understand the structure of the endosperm cell wall. Isolated walls were sequentially extracted with hot water (65°C), digested with lichenase ([1→3][1→4]-β-D-glucan 4-glucanohydrolase, EC 3.2.1.73), and then digested with endoxylanase. The final residue after consecutive hot-water extraction and digestion by the two enzymes was acid hydrolyzed for analysis of the monosaccharide composition by high-performance liquid chromatography (HPLC). The whole wall composition, as well as the composition of the fractions generated during hot-water extraction and enzymatic dissociation, was similar for the two cultivars of oats. The fractionation characteristics of the walls were consistent with a layered model : a relatively thin outer layer, adjacent to the middle lamella, consisting of an insoluble polysaccharide skeleton (cellulose and glucomannan) plus matrix polysaccharides (β-glucan and arabinoxylan), and a large inner layer of soluble polysaccharides (β-glucan and arabinoxylan). These layers correspond to the residue after hot-water extraction and the hot-water extract, respectively.