Abstract: This study was undertaken to explore the effects of processing methods on the quality of purple sweet potato juice. Raw, boiled and steamed purple sweet potato juices from the cultivar Yuzi 7 were prepared, and their sugar, anthocyanin ad total phenolic contents, browning index, antioxidant activity, color, sensory evaluation and aroma composition were compared. The experimental results showed that the 1,1-diphenyl-2-picrylhydrazyl radical (72.26%) and hydroxyl radical (81.27%) scavenging capacities of the raw juice were significantly higher than those of the boiled and steamed juices (P < 0.05), but it exhibited the highest browning degree and its color and aroma were not good. The content of anthocyanins (0.78 mg/100 g) in the steamed juice was significantly higher than that in the boiled and raw juices (P < 0.05), but its color was darker and its sensory and aroma quality were worse than that of the boiled juice. Although the antioxidant activity of the boiled juice was at a moderate level, its browning index (0.63) was significantly lower than the steamed and raw juices (P < 0.05). The boiled juice had better color and the highest comprehensive sensory score. It showed a translucent dark purple color and a soft taste as well as the best aroma quality. Totally 40 aroma components were identified, 21 of which were found in the boiled juice, accounting for 82.38% of the total peak area. Esters (28.19%) and alcohol (20.14%) were the major aroma components. Overall, the quality of the cooked juice was the best.

Key words: purple sweet potato juice, quality, aroma components, raw pulp processing method, boiling processing method, steaming processing method