ABSTRACT
Food polysaccharides, dissolved, dispersed, or suspended in water, are generally classified as gelling or nongelling. The former class is ordinarily transformed to gels by heat and/or special solutions, e.g., by alkali neutralization and electrolyte additions, such treatments having the effect of initially decomposing mostly hydrogen bonds in the solid solute, followed by its solvation (hydration), dissolution, and reformation as a gel, upon the cooling or neutralizing of the sol. Gelation is a function of other variables, e.g., the degree of polymerization (DP), solute concentration, and cosolute additions; but for most gums, temperature is the most important variable. Changes promoted by heating can be followed by differential scanning calorimetry (DSC). A DSC of curdlan (Fig. 1) showed a sharp endothermic peak at 50-64°C, possibly related to swelling and hydrogen-bond breakage; a broad endothermic peak between 70 and 120°C, and an exothermic peak in the range of 140-170°C. The swelling temperature decreased with increases in heating temperature. Heating (70-120°C) caused irreversible changes. Temperature hysteresis was observed between 60°C and 40°C. No exothermic peak at about 40°C developed on cooling after heating to 170°C. The strength of a gel depends on the temperature (Fig. 2).
