Physicochemical properties of sweetpotato starches with different gelatinization temperatures

Physicochemical properties of five sweetpotato starches differing in gelatinization temperature were examined. The gelatinization temperature of Koganesengan starch, an ordinary cultivar of sweetpotato in Japan, was 73.6 degrees C, whereas those of the other starches were measured to be 71.6 degrees C for Kyukei 96162-1, 65.8 degrees C for Kyushu No. 127, 63.9 degrees C for Kyukei 240, and 54.9 degrees C for Quick Sweet. Some relationships of the primary structural properties with the gelatinization temperature have been found. As the gelatinization temperature decreased: i) the content of phosphate groups attached to the glucosyl residues decreased, ii) the amylose content, which was determined as difference in long chains of debranched original starch and of its amylopectin, decreased, iii) the proportion of unit chains with DIP > 100 in the amylopectin fraction increased, iv) the proportion of unit chains with DIP 6 to 10 in the amylopectin fraction increased, whereas that of unit chains with DP 12 to 24 decreased, v) the B-type crystallinity of the starch granules was enhanced, and vi)the proportion of longer chains constituting each Nageli amylodextrin increased. Moreover, it was found that thin pastes of the low temperature-gelatinizing starches retrograded slower during cold storage than the ordinary starch. Among the starches, Quick Sweet starch granules, having the lowest gelatinization temperature, were digested rapidly by pancreatin.