Should we enhance the flavor of black tea by treating the plants with an injury compound?

Plants that are injured release volatile compounds that not only help to protect the plant but also “warn” surrounding plants which then produce defense compounds themselves. In previous posts we have discussed the effects of thrips and jassids in enhancing the aromas of second flush Darjeeling and Oriental Beauty Bai Hao teas respectively. Apparently you can have some of the same effects without the intervention of insects, simply by spraying the tea with one of the plant’s defensive volatile compounds, methyl jasmonate.

Shi and colleagues sprayed tea plants with methyl jasmonate in an alcohol solution 24 hours before plucking the bud and two leaves to create the tea. Control plants were sprayed with water. (One wonders what the alcohol might have contributed…though it probably evaporated quickly).*

The gene expression for two enzymes important for black tea aroma increased in the treated tea: β-primeverosidase and polyphenol oxidase. β-primeverosidase releases linalool, linalool oxides, and geraniol from the sugars to which they are bound, thus releasing their aroma. Polyphenol oxidase is important for the formation of theaflavins and thearubigens. Thus an increase in these enzymes may be expected to increase the quality of a black tea.

Indeed, methyl jasmonate noticeably altered the profile of aromatics in the resulting teas, with an increase in linalool and its oxides, which have a characteristic floral aroma, and a decrease in 3-hexen-1-ol, which has a rather bitter “green” smell. Other “green” cool/cold receptor activating chemicals decreased as well, with the result that a panel of tasters found the tea from treated leaves to be more honeyed, sweeter, and more floral. By decreasing the number of compounds that activate the cool/cold receptors, there is less inhibition of the warm/hot receptors, so the black-tea qualities of the tea stood out.

The fact is that we treat tea leaves at and after plucking in order to activate the injury responses in order to yield a more aromatic tea. The question is: should we be nudging the process by “fooling” the leaves into response-to-injury mode before they are even plucked?

Image below: a thrip (tiny brown strip-like object) on a petal of the tea Camellia in Darjeeling—natural aroma creation through insect injury. From a fascinating article about autumn harvest Darjeeling at Hojo Tea: http://hojotea.com/item_e/b06e.htm

* Jiang SHI, Li WANG, Cheng-ying MA, Hai-peng LU, Zong-mao CHEN, Zhi LIN.  Aroma changes of black tea prepared from methyl jasmonate treated tea plants. J Zhejiang Univ-Sci B (Biomed & Biotechnol) 2014 15(4):313-321.