Changes in Volatile Compounds of Sweet Potato Tips During Fermentation

Volatile compounds in fresh and fermented sweet potato tips at 0, 10, 20, 30, and 40 d during fermentation were investigated. A new parameter named "relative odor activity value (ROAV)" was applied in evaluating the contributions of volatile compounds to flavor, considering odor threshold. The results showed that volatile compounds could be clustered in the following chemical families: alkenes (most of them were sesquiterpene), alcohols, aldehydes, ketones, and esters in decreasing order. During fermentation, the concentrations of alkenes and ketones were increased and then decreased continuously. Alcohols and esters were increased; while the concentrations of aldehydes decreased. Interestingly, fermenting processes (0-20 d) may contribute to the increase of alkenes and ketones. Major compounds that were identified in all samples include alpha- and beta-caryophyllene, beta- and gamma-elemene, and beta-cubebene (in decreasing order). The changes of their concentrations during fermentation were the same as that of alkenes. Caryophyllene was abundant in all of the samples examined. It has anti-tumour, anti-inflammatory and anti-pests activities. It can mediate interactions among plant, herbivores and their natural enemies. beta- and gamma-elemene, which have been used as antitumor drugs, have not been reported previously as volatiles from sweet potato tips. beta-cubebene with antioxidant activity can be used as natural preservatives in food and/or by the pharmaceutical industry.