Non-Starchy Polysaccharides of Cereal Grains V. Some Hemicellulose Fractions

Hemicelluloses extractable from cereal grains (after removal of starch and cereal gums) by means of 4% aq. sodium hydroxide solution in the cold appear to be of two types. Husk-type hemicelluloses are found abundantly in the husk, integuments and perisperm, but are dispersed in smaller proportion throughout the grain; hemicelluloses now described from husk contain uronic acid residues, are rich in pentosan units, have relatively low specific viscosity, and resemble hemicelluloses isolated from cereal straws and the like. The typical endospermic hemicelluloses are substantially free from uronic acid residues, contain moderate to large proportions of glucosan, and have high specific viscosity; the endospermic hemicelluloses act as gum precursors during autolysis or germination, but their solubilization involves a decrease in the xylan/araban ratio of pentosan-rich fractions. The endospermic hemicelluloses of barley are rich in glucosan units, but in those from wheat pentosan predominates; this pattern of distributions parallels that already shown to hold for the gums from these cereals.