Effects of Dryness on the Sweetness of Steamed and Dried Slices of ‘Kenroku’ Sweet Potato

Abstract

The sweetness of ‘Kenroku’ sweet potato slices that are steamed and then dried rapidly decreases during the drying process. This rapid loss of sweetness could not be due to sugar degradation. We hypothesized that hardening of the slices concurrent with rapid drying decreases the sweetness release efficiency. The balance of these two opposing effects (increase in sugar concentration and decrease in sweetness release efficiency), both caused by drying, determines the optimal extent to which the slices should be dried in order to maximize the sweetness. We conducted repetitive simple sensory evaluations comparing pairs of slices dried at 30 °C for different drying times. In our experimental condition, maximal sweetness was achieved by drying the slices for 17 h. The drying time showed strong correlations with moisture content, hardness measured by the fruit hardness tester KM-1, and Brix of slices. The optimal values of these parameters were 30.6%, 0.89 kg, and 48.4%, respectively. Older subjects participating in the sensory evaluations tended to prefer the texture of existing products dried for more than 17 h, whereas younger subjects preferred the sweetest slices over the existing products. These results imply that sweeter and softer steamed and dried slices prepared with a shorter drying time than the existing products could appeal to a larger population and increase the demand of these products.