Effect of sugars and sugar alcohols on freezing behavior of corn starch gel as monitored by time domain 1H NMR spectroscopy

The freezing behavior of corn starch gels (40% starch solids) with 11 different sugars and sugar alcohols (10 or 30% based on starch weight) was investigated using time domain 1H NMR spectroscopy. As estimated from the liquid signal intensity curve, the ice melting temperature linearly decreased and the relative amount of solid glass formed increased with the molar concentration of the added sugars. The observed ice melting temperatures were low (approximately −10 °C for non-sugar gel), because of the non-equilibrium state produced by rapid cooling (20 °C/min) and the large sample size. Sugar addition (up to 30%) depressed the ice melting temperature of the gel system by more than 10 °C. Sugar addition and rapid-cooling promoted solid glass formation in the freeze-concentrated solution with a consequent reduction in liquid mobility. The unfrozen liquid levels resolved from the relative liquid signal intensity data were not colligatively governed, showing a dependence on sugar structure. Among the sugars tested, the unfrozen liquid level produced by a sugar corresponded in the order: hexose>pentose, isomaltose>sucrose>trehalose>maltose. The sugar alcohols exhibited higher unfrozen liquid levels than did the corresponding sugars.