The crystallinity of amylose and amylopectin films

Abstract

X-ray crystallinity of amylose and amylopectin films with 0, 10 and 30% of glycerol and stored at RH 0, 54 and 91% were studied. Films prepared of water cast dilute solutions and dried at 70°C were thin and transparent. Each fresh amylose film showed B-type crystalline structures, and depending on the glycerol and water contents the amount of crystallinity varied from 6 to 32%. No changes in the crystallinity of the amylose films were observed during storage of two months. The fresh amylopectin films were completely amorphous. After storage for two months at the highest humidity the amylopectin film with 30% glycerol showed crystalline structure (19%), but all other amylopectin films remained amorphous during ageing. The crystal formation in the highly plasticised amylopectin film was suggested to be due to its rubbery state under the storage conditions. Amylose films were stable in water unlike amylopectin films that dispersed fast in water. About 35% of the amylose films were resistant to α-amylase, whereas amylopectin films were hydrolysed wholly. Also when treated with hydrochloric acid the amylopectin films dissolved totally and fast, while one week was needed to dissolve about 50% of the amylose films. It was concluded that even if part of the amylose films were amorphous, also these amorphous regions were more resistant to hydrolysis than the amorphous amylopectin structures.