Physicochemical Properties of Starches from Recently Bred Sweetpotatoes in Japan

Abstract

The physicochemical properties of starches from 10 sweetpotato varieties differing in tuberous root traits, recently bred in Japan, were examined using our standard experimental methods. Pasting and gelatinization properties determined by a rapid visco-analyser and a differential scanning calorimeter, respectively, grouped the sweetpotato starches roughly into two types. One was an ordinary sweetpotato starch type, well known as traditional sweetpotato starch; the other was a starch type, having low gelatinization temperature as represented by Quick Sweet. The apparent amylose contents of the starches were similar ranging from 18.6 to 20.7%, whereas phosphate contents and granular sizes ranged widely from 1.13 to 7.53 μmol/g and from 12.8 to 18.6 μm, respectively. The chain length distributions of the starches were classified into two types, similar to the pasting and gelatinization types. In this study, for the quantitative comparison of chain length distribution, we successfully performed an analysis yielding a number-based chain length distribution of amylopectin, estimated by gel permeation chromatography with a refractive index detector and using calibration with commercial pullulan standards. With respect to functional properties, retrogradation of starch pastes and digestibility of starch granules by glucoamylase showed measurably large differences among the starches, depending on minor differences in structural properties.