Starches of the Wrinkled and the Smooth Pea

Abstract

WE wish to report some observations concerning the chemical constitution of pea starch which may influence current views on the part played by this polysaccharide in plant metabolism. The form of the starch grain is often characteristic of the plant or plant organ in which the starch is found, but in most of the common starch-bearing plants this difference in grain-form is not reflected in the chemical composition of the starch. By composition is meant, in this context, the relative proportions of the amylose (unbranched chain) and amylopectin (branched chain) components of the starch. Most of the cereal and root starches are composed of 20–30 per cent amylose and 70–80 per cent amylopectin. Until recently, the only exceptional starches which had been examined were those of the waxy (or glutinous) variety of cereals. Thus, waxy maize starch, which has a low gelatinization temperature and is stained reddish-purple with iodine (B.V. 0·10), owes these properties to the fact that it contains little, if any, amylose, being composed almost entirely of the branched-chain component.