A DSC STUDY OF THE EFFECTS OF SUGARS ON THERMAL-PROPERTIES OF RICE STARCH GELS BEFORE AND AFTER AGING

Thermal characterization of gelatinized binary rice starch-water and t ernary starch-sugar-water gels before and after aging was carried out using differential scanning calorimetry The glass transition temperatu re of the maximally freeze-concentrated solution (T-g') in both fresh and aged gels was observed to decrease progressively with increasing s ugar concentration. Aging of the gels generally shifted T-g' to higher temperatures, but had little or no effect on the ice melting peak tem perature (T-m). The presence of various sugars could either accelerate or retard starch (amylopectin) recrystallization, depending on the ty pe and concentration of sugar, as well as on starch/water ratio. A hyp othesis based on the dual antiplasticizing-plasticizing effects of sug ars was postulated to explain the observed effects. Of the sugars stud ied, xylose and fructose appeared to display exceptional retardative a nd accelerative effects, respectively, on retrogradation.