The barley grain consists of a small embryo and a large storage tissue, the endosperm,
surrounded by the husk (Fig.1). About 90% of the endosperm is starch localized in large dead
cells packed with starch granules and storage proteins and surrounded by a living aleurone
layer composed of small, thick-walled cells. The cell walls consist of a number of different
non-starch structural polysaccharides. The most prominent of these, β-glucan, a linear
polymer of glucose joined by β(1→3) and β(1→4) linkages, accounts for 70% of the cell wall
components together with arabinoxylan (15%). The latter consists of β(1→3) linked xylose
chains to which are attached arabinose units. Several minor components identified in the cell
wall include glucomannan (3%) as well as protein (5%).