Physicochemical Properties of Nagaimo (Yam) Starch

Abstract

Starch was isolated from rhizomes of Nagaimo (a kind of yam), and its structural and functional properties were investigated in detail. It was found to contain 22% of amylose on the basis of iodine affinity and 129ppm of phosphorus, of which 66% was bound at C-6 of glucosyl residues. The number- and weight-average degrees of polymerization were 2, 000 and 6, 300, respectively. The average chain-length of amylose was 525 and the molecules were composed of approximately four chains on average. The number- and weight-average chain-lengths of amylopectin were 24 and 28, respectively. The chain length showed a characteristic trimodal distribution on high performance gel-chromatography. The onset of gelatinization was observed at 65°C on photopastegraphy. The Brabendor amylogram (4% concentration) showed a sharp increase in viscosity at 66°C, a maximum viscosity of 695 B. U. and considerable break down (270 B. U.). The retrogradation tendency of a 5% aqueous paste of it stored at 0°C was a little greater than those of potato and kuzu starches. The granules showed the B-type X-ray diffraction pattern.