MOLECULAR-STRUCTURE OF A LOW-AMYLOPECTIN STARCH AND OTHER HIGH-AMYLOSE MAIZE STARCHES

The molecular structure of two commercially available high-amylose mai ze starches, HYLON(R) V starch and HYLON(R) VII starch, and of a newly developed low-amylopectin starch (WPS) was examined. These high-amylo se starches give three apparent fractions as determined by gel-permeat ion chromatography: a high-molecular weight (mol.wt) amylopectin fract ion, a low-molwt amylose fraction, and an intermediate-mol. wt fractio n which contains both linear and branched components. The low-mol.wt a mylose fraction increases from 9.4% in HYLON V starch to 17.7% in HYLO N VII starch and 26.5% in LAPS, whereas the high-mol.wt amylopectin fr action decreases from 31.1% in HYLON V starch to 13.8% in HYLON VII st arch and 2.5% in LAPS. The percentage of linear components in HYLON V starch, HYLON VII starch, and LAPS are 42, 54, and 80%, respectively. High-amylose starches have a large proportion of long chains in their branched fractions compared to waxy-maize and normal-maize starch. Bot h HYLON VII starch and the LAPS give B plus V-type X-ray diffraction p atterns, but the LAPS has even a higher gelatinization temperature, lo wer swelling power in hot water, and is more resistant to acid digesti on. With the lack of amylopectin, amylose accounts for at least part o f the double helical structure in the LAPS granules. (C) 1998 Academic Press Limited.