Maintaining the Anthocyanin Content and Improvement of the Aroma of an Alcoholic Fermented Beverage Produced from Raw Purple-Fleshed Sweet Potato

Abstract

We have been developing and studying an alcoholic fermented beverage produced from a raw purple-fleshed sweet potato cultivar (Ipomoea babatas cv. Ayamurasaki) containing high amounts of anthocyanin. In this study, we investigated the relationship between the anthocyanin content and aroma of the beverage and its manufacturing process. When raw sweet potatoes were allowed to stand for 1h at 5°C or 30°C between grinding and the initiation of fermentation, the anthocyanin content of the resulting beverage was considerably lower than that of an otherwise identical beverage produced from sweet potatoes ground immediately before fermentation. With that in mind, we investigated the effect of pH on maintenance of the anthocyanin content of ground sweet potato and found that decreasing the pH to 3.0 with citric or lactic acid made it possible to allow the ground sweet potatoes to stand for 3h at 30°C before starting fermentation, without any loss of anthocyanin. Moreover, the addition of citric acid led to the production of large amounts of higher alcohols such as isoamyl alcohol and isobutyl alcohol. These findings suggest that citric acid has desirable effects on both the color and the aroma of the alcoholic fermented beverage produced from raw purple-fleshed sweet potato.