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The effect of water-soluble sugars contained in sweet potato on gelatinization and retrogradation of starch was studied by means of differential scanning calorimetry. Gelatinization peak temperature Tp and gelatinization enthalpy increased with increasing sugar concentration. The shift of T p to higher temperatures was attributed to the stabilization of the crystalline region in starch and the immobilization of water by sugar molecules. The effect is larger in the order sucrose, glucose, fructose. All these sugars prevent retrogradation of sweet potato starch paste, and the order of effectiveness is the same as in the case of increase in gelatinization temperature. The effect of sucrose concentration on Tp was explained by a zipper model approach.

The effects of food texture on the chewing patterns of elderly and young people, masticatory recordings using electromyography (EMG) were carried out.Fourteen French adults (mean 29.4 years) and 23 elderly (mean 67.7 years) participated. Six food products (rice, be& cheese, crispy bread, apple and peanuts) were tested. The chewing pattern of elderly subjects was characterized by a significant increase of number of chews and chewing duration for all foods except rice. Whatever the food type, muscle activity per chew (mean amplitude x burst duration) was lower for elderly than for young subjects. Single chews appeared less efsective for food reduction in elderly than in young subjects. This can be partly compensated for by increasing the chewing duration and number of chews. No significant difference was found between both groups of subject for the total amount of EMG activity required prior to swallow whatever the food chewed.