Pea starch, a starch of high amylose content.

Two general classes of starch have been recognized up to the present time, the common starches, containing both amylose and amylopectin molecules, and the waxy or glutinous cereal starches, which are comprised almost entirely of amylopectin. The first class can, in turn, be subdivided into two broad groups, one composed of the so called root starches, such as t’apioca, potato, a,nd sweet potato starch, which contain about 17 to 22 per cent amylose, and the other comprising the cereal starches which contain approximately 25 to 29 per cent amylose. The differences in physical properties exhibited by pastes, sols, and gels of starches of these two groups result, in part, from the difference in the ratio of amylose to amylopectin molecules; i.e., of linear to non-linear molecules. Other important factors influence the differences in physical characteristics of starch-water systems of the two groups; these include the average chain length of the amylose, the amount of phosphoric acid directly bound to the amylopectin, and the degree of association of amylose and amylopectin. One starch in a possible third group containing slightly over 30 per cent amylose has been described (1). This was obtained from Easter lily bulbs. Its paste characteristics are more like those of corn-starch than of the root starches and it may belong with the cereal starch group. Mr. J. P. Nielsen of the Western Regional Research Laboratory noted, during a study of the colors given by a number of starches with iodine, that a peculiar coloration was obtained in the case of starch from garden type, wrinkled seeded peas (2). On the basis of this color, he believed the amylose content of wrinkled seeded pea starch to be exceptionally high, and estimated it to be about 75 per cent. Mr. Nielsen called this conclusion to the attention of the authors. Apparently the only other experimental work on pea starch was that carried out by Reichert (3) who reported no unusual characteristics. Because a starch having such a high content of amylose would be unique and might have unusual physical properties, a thorough study of it, as suggested by Mr. Nielsen, appeared desirable. Starch was therefore prepared from wrinkled seeded peas, and