Effects of sugars and sugar alcohols on thermal transition and cold stability of corn starch gel

Various sugars and sugar alcohols (ribose, xylose, glucose, fructose, mannose, sucrose, maltose, isomaltose, trehalose, xylitol, mannitol, and sorbitol) were compared in their effects on thermal transitions and cold-storage stability of a corn starch–sugar gel (40% starch, starch:sugar=10:1 or 10:3 dry solids basis) using a differential scanning calorimetry. As the molar concentration of sugar increased, the onset temperature and enthalpy for starch melting were increased. Among the sugars, the samples with disaccharides exhibited higher onset temperature and enthalpy than those with monosaccharides at the same molar concentration. Under cold storage (4 or −20 °C), the sugars facilitated amylopectin recrystallization. Fructose and isomaltose produced higher degrees of amylopectin recrystallization than did other sugars. Sugar alcohols produced slightly greater recrystallization than did the corresponding sugars. Ice melting temperature and glass transition temperature (T′g) of the freeze-concentrated phase were decreased as the molar concentration of sugars increased, and there was no or little dependence on the chemical structure of sugars. Ice melting enthalpy for the gels showed no clear dependence on sugar concentration or structure. Sucrose addition lowered the ice melting enthalpy (ice formation by rapid freezing), whereas isomaltose or trehalose addition raised it. By cold storage, the T′g of the starch gels was increased, whereas the ice melting enthalpy was decreased, as a result of water consumption for starch recrystallization. In the gel system (40% starch), sugar addition (10 or 30% based on starch) enhanced starch recrystallization, but decreased the ice melting and glass transition temperatures.