Cereal Chem 51:389 - 405. | VIEW
Lintnerized Starches. Gel Filtration and Enzymatic Studies of Insoluble Residues from Prolonged Acid Treatment of Potato Starch.
J. P. Robin, C. Mercier, R. Charbonniere, and A. Guilbot. Copyright 1974 by the American Association of Cereal Chemists, Inc.
Granular potato starch was hydrolyzed with 2.2N hydrochloric acid (HCl) at 35 C. for periods of time up to 40 days. After removal of the acid and soluble carbohydrates, the residues (lintnerized potato starches) were washed with deionized water and dried to 10% moisture. When the percentage of solubilized carbohydrate was plotted vs. time, the curve showed two different steps. The first step, with a high rate, was attributed to hydrolysis of the amorphous part of starch granules, and the second step, with a lower rate, to hydrolysis of the more organized areas. X-ray patterns, apparent amylose content, and iodine absorption spectra of the HCl residues were determined. Sephadex G-50 gel-permeation chromatography of the dissolved residues was performed directly and after successive enzymatic digests with pullulanase and beta-amylase. The results show the progressive appearance of two major chain populations: II, DP*?* 25, and III, DP*?* 15. II was identified enzymatically as being singly branched, and III, primarily as linear chains. III appears as the more acid-resistant and crystalline part of the starch granules, as confirmed by X-ray diffraction. From the molecular size of III, the calculated dimension of the starch crystallites would be about 60 Angstroms in the chain axis direction. The amylose fraction is rapidly degraded, and there is no evidence for amylose participation in the crystalline areas. Amylopectin chains are primarily responsible for the crystallinity of starch, imposing the crystallite dimension. The chains of DP*?* 15 which constitute these crystallites could originate from degraded amylose chains, or from the external A-chains or internal chains of amylopectin. These results lead to a new model of amylopectin containing clusters of highly ordered DP*?* 15 chains.