The floral aroma of jasmine tea contains indole, a compound that on its own is also described as fecal or animalic. A 2017 analysis found that indole increased in green tea scented with jasmine flowers and identified it, together with linalool, β-ionone, and methyl anthranilate, as a likely major contributor to the aroma.
The research was about more than discovering an unexpected ingredient. It examined differences between compounds that readily pass from flowers into tea and those that are less well retained, as well as changes caused by heating during manufacture, to explore how jasmine tea’s aroma is assembled.
Mixing flowers with tea and drying it, three times
The study used green tea made from young shoots of the Jinxuan cultivar grown in Guangxi, China, and open flowers of the jasmine species Jasminum sambac. The green tea was manufactured first, then mixed with the flowers at a flower-to-tea weight ratio of 4:5.
After 12 hours at 38–48°C, the flowers were removed and the leaves dried at 120°C for one hour. This scenting and drying sequence was performed three times in total. Although the paper’s introduction also describes general drying conditions, this experiment used 120°C.
The researchers compared volatile compounds in scented tea, unscented tea, and fresh flowers. For tea, they added 100 milliliters of boiling water to one gram of leaves and left it for five minutes, then collected compounds released into the air above the infusion onto a fiber for GC-MS analysis. Compounds around the flowers were collected separately at 38°C. Three biological replicates were examined for each sample type.
The most abundant compounds in flowers do not necessarily dominate tea
Compared with unscented tea, 34 compounds increased and three decreased in the scented tea. Linalool, indole, and benzyl acetate, for example, increased substantially. These findings were consistent with uptake of these compounds from the flowers into the tea.
By contrast, α-farnesene, the most abundant compound around the flowers, was much less abundant in the scented tea. Looking only at the amounts of compounds in flowers therefore does not directly predict the composition of the aroma released when the tea is drunk.
Sampling conditions differed between the tea infusions and fresh flowers, and the fraction of each compound released from a sample into the air was unknown. The authors also noted the limitations of simply comparing these two sets of measurements directly.
Indole is another candidate contributor to the floral aroma
The amount of a compound and the concentration at which people begin to smell it are different things. For 27 compounds with thresholds available in the literature, the researchers calculated odor activity values, or OAVs, by dividing the measured amount by the threshold. Compounds with high OAVs are strong candidates when considering contributions to aroma.
In the scented tea, β-ionone had an OAV of 731.3 and linalool an OAV of 288.9, both higher than in unscented tea. Indole and methyl anthranilate were also among the compounds considered likely to be important.
The odor descriptions compiled in the paper characterize linalool as floral, fruity, and citrus-like, ionone as woody and floral, and indole as fecal, animalic, and floral. This combination illustrates why descriptions of a single compound do not necessarily match the overall impression of a tea containing it.
An OAV is a ratio relative to a detection threshold, not a multiplier of perceived intensity meaning that an aroma is 731 times stronger. The study also did not ask drinkers whether adding indole made the tea more pleasant, or remove particular compounds to test changes in aroma. Contributions to the mixed aroma were inferred from the analysis.
Retention in tea varies considerably among compounds
The researchers also calculated a measure called scenting efficiency, comparing the increase caused by scenting with the measured amount in the flowers. Values ranged widely, from 0.22% for α-farnesene to 75.5% for β-myrcene.
This was not, however, a transfer percentage obtained by tracking the entire mass of a compound from flowers to tea. As noted above, sampling conditions differed between flowers and infusions, and some compounds might also have formed within the tea. These values are indicators of relative retention under the analytical conditions used.
The authors noted that many water-soluble compounds had high values. They suggested that tea leaves might absorb moisture released by the flowers, with aroma compounds taken up into that water. Yet some poorly water-soluble compounds, such as myrcene and limonene, also had high values. They therefore considered several properties, including volatility and interactions with tea leaves, to be involved.
Heating can both create aroma compounds and remove them
Some compounds that increased in scented tea were not detected around the flowers in this experiment, including β-ionone and some oxygenated terpenes. The authors discussed the possibility that, alongside direct uptake from flowers, heat- or moisture-related conversion of precursors contributed to these increases.
Conversely, nonanal and decanal, described as having waxy or fatty odor notes, decreased in the scented tea. Repeated heating might have released them from the leaves into the air.
Because the experiment did not directly trace formation pathways or losses, the contribution of each reaction remains uncertain. Even so, simply describing floral scent as adhering to tea leaves cannot account for the full pattern of increases and decreases. The authors concluded that considering uptake, retention, release, and chemical change together could help in designing tea aromas during manufacture.
Summary
In green tea scented with jasmine, compounds including linalool and indole increased and were considered likely to make important contributions to the floral aroma. Meanwhile, α-farnesene, abundant in the flowers, was not retained to the same extent, and other compounds, including nonanal, decreased.
Rather than being a wholesale transfer of floral compounds, jasmine tea’s aroma reflects what the leaves absorb, what heating creates, and what is lost. Even an unexpected ingredient such as indole can provide a clue to understanding floral scent when considered as part of that whole.
The research was supported by the National Natural Science Foundation of China. The authors declared no conflicts of interest.
Reference
Shen J-X, Rana MM, Liu G-F, Ling T-J, Gruber MY, Wei S. Differential Contribution of Jasmine Floral Volatiles to the Aroma of Scented Green Tea. Journal of Food Quality. 2017;5849501. doi:10.1155/2017/5849501
