Effect of Cultivar and Growth Conditions on Starch Properties of Sweet Potatoes

Abstract

1. Starches were prepared from many kinds of sweet potatoes, which are mainly used for starch production, differing in variety, stage of development and tissue zone. Average granule size, amy lose content, gelatinization properties by differential scanning calorimetry and digestibility of raw starch by glucoamylase were compared. Digestibility by glucoamylase tended to be higher in the earlier stage of development and the cambium zone. Further, correlations among these starch properties were calculated to determine the factors relating to digestibility of raw starch by glucoamy lase. Negative correlations were observed between gelatinization heat and digestibility as well as average granule size and digestibility. 2. Starches were also prepared from many kinds of purple-and orange-fleshed sweet potatoes to investigate the effect of the cultivation conditions on starch properties. Earlier planting and harvesting dates apparently enhanced gelatinization temperature and tended to reduce the content of short chains of amylopectin. A major difference in starch properties, especially gelatinization temperature and amylopectin structure, occurs according to soil tem perature during the development of sweet potato tuberous roots. To elucidate the extensive variation in starch gelatinization properties within the same botanical origin for sweet potato, correlations were determined between gelatinization parameters and starch molecular characteristics. Starch with a lower gelatinization temperature had relatively abundant extremely shorter unit-chains of amylopectin.