The Retrogradation of Starch Gels and Starch Properties from Various Kinds of Sweet Potato Starches

Abstract

The retrogradation of starch gels from 5 kinds of sweet potato cultivars (Shiroyutaka, Satumastarch, Joywhite, Kyushu No. 123 and Kyushu No. 126) were compared, and the relationship between properties of starch and molecular structure of amylopectin was also investigated. Considerable differences in the retrogradation of sweet potato starch gels were found in each varietiy . In Joywhite, Kyushu No. 123 and Satumastarch, retrogradation for starch gels was slow. The varieties of starches with slow rate of retrogradation showed common characteristics: the pasting temperature is low, and both the phosphorus content and amylose content are low. In addition, the degree of gelatinization determined by the beta-amylase-pullulanase method was correlated with the tendency of retrogradation of sweet potato starch gels. The chain length distribution of isoamylasedebranched amylopectin by gel permeation chromatography (GPC) showed that the content of long chains was low in varieties with slow rate of retrogradation. High performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) of isoamylase-debranched amylopectin showed that the content of short chains with DP 6-10 was high and the content of chains with DP 11-17 was low in varieties with a slow rate of retrogradation. The GPC analysis of the phosphorylated chains revealed that the phosphorus of sweet potato starch was attached to the long chains of amylopectin. Thus, these results suggest that the molecular structure of amylopectin is related to the phosphorus content, which also influences the retrogradation properties.