Flavor Contribution and Formation of Epoxydecenal Isomers in Black Tea

摘要

Two potent odorants responsible for the juicy and sweet note in black tea were identified as cis- and trans-4,5-epoxy-(E)-2-decenals. Of the two odorants, cis-4,5-epoxy-(E)-2-decenal has been identified for the first time in black tea, and it was assumed that both isomers in black tea were formed from linoleic acid in the tea leaves via 12,13-epoxy-9-hydroperoxy-10-octadecenoic acid. In addition, the following formation mechanism during black tea production was assumed. First, the withering and fermentation processes convert linoleic acid to its hydroperoxide in which the oxygen adds to the 13 carbon due to lipoxygenase activity. Subsequently, by heating during the drying process, the 13-hydroperoxide of linoleic acid produces epoxydecenal isomers via the cis- and trans-epoxyallylic radicals which are intermediates of 12,13-epoxy-9-hydroperoxy-10-octadecenoic acid. Furthermore, by application of aroma extract dilution analysis (AEDA) on the black tea infusion (Dimbula), it was found that these isomers were significantly important odorants for the flavor attribute of Dimbula, because they had high flavor dilution (FD) factors and a "sweet-juicy" odor quality.