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This study investigated the thermal degradation characteristics of fructose. A 20% fructose solution was heated to 110-150°C for 1-5 hours. Chromaticity, pH, organic acid, 5-hydroxymethylfurfural (HMF), fructose content, electron-donating ability (EDA) (as a percentage), and ascorbic acid (AA) equivalent antioxidant capacity (AEAC) of heated fructose solutions were evaluated. With increasing heating temperature and time, the L-value decreased, and the a- and b-values increased to 120°C for 4 hours and 2 hours, respectively, and then decreased thereafter; however, total color difference increased. The pH and fructose content decreased. Organic acids, such as formic acid, lactic acid, and levulinic acid, and HMF content increased with increasing heating temperature and time. Antioxidant activity increased with increasing heating temperature and time (no antioxidant activity in 20% fructose solution). The EDAs after heating at 130°C for 3 and 4 hours were 17.21% and 31.73%, respectively, and the highest antioxidant activity was 94.57% (150°C for 4 hours). The AEAC was 1.71 mg of AA eq/g before heating and 24.43 mg of AA eq/g after heating at 150°C for 4 hours. These results suggest that heat treatment may be a useful method for increasing the antioxidant activity of fluid foodstuffs such as fruit juices and fructose-containing foods.

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This study investigated the quality characteristics of pastes prepared by different heat treatment methods using three varieties of sweet potatoes with varying colors. The free sugars, viz., fructose, glucose, and sucrose, are normally detected in the sweet potato, with additional detection of maltose when made into a paste. The total sugar content of the paste with heat treatment methods ranged between 17.61% to 20.39% for Daeyumi, 17.29% to 22.41% for Sinjami, and 14.48% to 17.66% for Juhwangmi, with the highest values obtained after being subjected to baking. The total polyphenol and flavonoid contents of the paste were highest in the Sinjami cultivar for all heat treatment methods. The extrusion force ranged from 81.24 to 140.31 N.s. and was highest in the Daeyumi variety, and in baking. Results of the sensory evaluation test revealed that baking was the most suitable heat treatment method. Moreover, our results indicate that Sinjami is valuable as a functional sweet potato paste due to its high total polyphenol and flavonoid content.