Chapter 12
Flavor Contribution and Formation of Epoxydecenal Isomers in Black Tea
Downloaded by UNIV QUEENSLAND on April 30, 2013 | http://pubs.acs.org Publication Date: September 30, 2008 | doi: 10.1021/bk-2008-0988.ch012
Kenji Kumazawa, Yoshiyuki Wada, and Hideki Masuda Ogawa and Company, Ltd., 15-7 Chidori Urayasushi, Chiba 279-0032, Japan
Two potent odorants responsible for the juicy and sweet note in black tea were identified as cis- and trans-4,5-epoxy-(E)-2decenals. 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-hydroperoxy10-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 transepoxyallylic radicals which are intermediates of 12,13-epoxy9-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.
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© 2008 American Chemical Society In Food Flavor; Tamura, H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
Downloaded by UNIV QUEENSLAND on April 30, 2013 | http://pubs.acs.org Publication Date: September 30, 2008 | doi: 10.1021/bk-2008-0988.ch012
137 The steps involved in the processing of black tea include withering, leaf disruption (rolling and/or cutting), fermentation, drying and grading. For the characteristic process during black tea production, it utilizes an enzyme reaction. Namely, black tea leaves are processed by drying after making use of sufficient enzyme action during the withering and fermentation processes. On the other hand, the enzymes in green tea leaves are inactivated by steaming or parching during the first process, and there is only slight enzymatic action. Black tea flavor is quite different from that of green tea regardless of being made from the same kind of plant. For the flavor formation in black tea, in particular, it was pointed out that the enzyme action during the manufacturing process is very important (1-4). However, the influence of the enzyme action during the manufacturing process on the formation of the potent odorants is still mostly unresolved. rAmy-4,5-Epoxy-(£)-2-decenal has been identified as a contributor to the aroma of black tea using AEDA (5, 6). On the basis of previous research on lipid degradation products, #-
