Purification and structure of amylose from rice starch

A method for the purification of amylose from rice starch has been developed. The critical step was the removal of insoluble amylopectin-like contamination from crude amylose in water at 50° by ultracentrifugation at 100,000g for 1 h. The conventional autoclaving procedure was avoided. Gel-permeation chromatography and h.p.l.c. indicated the amylose specimens prepared from indica and japonica rice starches to be pure. The iodine affinities and blue values of the specimens were 20.0–21.1 g/100 g and 1.40–1.47, respectively. The amyloses had number-average d.p. (d.p.n) values of 980–1110, average chain-lengths of 250–370, and beta-amylolysis limits of 73–84%, indicating them to be slightly branched molecules with 2–5 chains on average. The weight-average d.p. (d.p.w) values were 2750–3320, and the high d.p.w/d.p.n values (2.6–3.4) suggested broad distributions of molecular weights.