World Tea Expo Day 3: about Selena Ahmed’s Skill Building Workshop “Taste & Tea Chemistry.“

On Friday morning I had the good fortune to attend Selena Ahmed’s skill building workshop, “Taste & Tea Chemistry.“

Selena is Assistant Professor of Sustainable Food and Bioenergy Systems at the University of Montana at Bozeman, where she studies the effects of the environment on the chemicals (and therefore the flavors) in tea. As her university webpage indicates, “Her focal study system is tea agro-forestry and subsistence food systems in China’s Yunnan Province in the context of climate change and dietary transition.”  A major point she made, to quote from one of her papers: “The taste of plants, particularly bitterness, may guide societies in the search for medicinal plants and beneficial phytochemicals.” *

In her workshop we offered some tastes, such as the taste of caffeine, one of the methylxanthines (along with theobromine) in tea (note that theophylline, another methylxanthine, is rarely if ever in tea).

Here is the diagram Selena showed to accompany these tastes:

http://www.ramenchemistry.com/blog/2015/2/7/umami-science-part-ii-umami-discovered

You can see some squiggly lines next to some letters. These represent the receptors for each taste. The bitter receptor in the lower right corner. As you can see it has two tails and loops in between. The upper tail sticks out of the taste bud cell and grabs on to the bitter chemical. The loops serve to anchor the receptor in the cell membrane, and the lower tail sticks into the inside of the cell. When the upper tail has a bitter chemical attached to it, the lower tail changes shape, and starts a series of reactions inside the cell that leads to our perception of bitter.

Caffeine is bitter, though not to equally bitter to everyone. One of the reason for variation lies in individual differences in the structures of the bitter taste receptors. There are about 40 different bitter receptor molecule structures, each of which is coded by a gene in the cell’s DNA. The gene for a receptor for caffeine, TAS2R43, is known to vary from person to person, and leads to differences in coffee liking. **

Next we tasted glutamate, a major chemical for umami taste. Sixty percent of glutamate in muscle exists as free glutamate, that is, not built into a protein. Thus when we bite into a piece of meat, the taste we get is primarily that of glutamate. It was interesting to me that the participants had difficulty both in detecting and then in naming the flavor. We are well accustomed to sensing the other tastes, but umami is elusive. As Selena pointed out in her slide, our appreciation of umami as a specific taste came late in history, and came thanks to the work of Kikunae Ikeda, a chemist at Tokyo Imperial University—his paper is dated 1909. He noticed that Japanese seaweed has a taste that was different from the usual four, and proceeded to discover that glutamate contributed a specific taste that he called “umami.” The discovery of specific receptors for umami taste on taste bud cells further solidified the notion that umami is a specific taste.

Finally we tasted gamma-amino butyric acid (GABA)—had never tasted it before. GABA is supposed to have a meaty umami taste, though I can’t say I tasted it very clearly. GABA is an odd chemical in that it is a neurotransmitter that dampens nerve function throughout the nervous system. It is present in a number of teas, especially pu-erh, and has been said to contribute to the soothing effects of this tea. Interestingly, it can be used at very low concentrations together with naringenin from oranges to reduce bitterness and mineral tastes (see patent: https://www.google.com/patents/US20140170082)

Then came some of the aroma chemicals we find in tea. The first was nerolidol, which to my great shame I did not specifically recognize, even though I had use it in my own talk, and therefore had spent a good deal of time smelling it during the past months. To me, nerolidol is the faintest of smells, rose-like, yet woody. The word elusive again comes to mind.

But I did hit geraniol on the nose (if I may say it that way). Geraniol is one of the trio of monoterpenoids— linalool, geraniol, and nerol—that can be found in virtually every tea, and also in roses, where they give the flowers their characteristic cool smell. Geraniol, not surprisingly, can be found in geraniums—that slightly “off” geranium smell that catches you in the throat comes in part from geraniol. The “catch” part  comes from activation of the cold TRPA1 receptor on the trigeminal nerve.

All in all there were 10 smells, from linalool with its fresh rose smell, to two different pine-related compounds, terpineol and pinene, to citrus aromas. Our table had a lot of fun figuring out how to describe each one. 

The climax of the workshop was tasting high mountain versus low mountain oolongs, and high mountain oolongs from the spring and the summer (monsoon) season. The first pair were both from a spring harvest, processed more or less in the same way, and yet were as different as night and day. The high mountain was highly floral and fruity, whereas the low mountain was distinctly less so, and more woody.  And the monsoon tea was so flat compared with the spring tea. These differences can be explained by the striking differences in composition that Professor Ahmed showed us—a clear example of the effects of environment on tea.

Here I am in my pink outfit with (left to right) my table companions Tico Aran of JoJo Tea Miami, Kuei-Chen Fang, of Jhentea, Taiwan and New York, Matthew Berning from the National Society of Collegiate Tea Drinkers, and Marzi Pecen, tea connoisseur, teacher, and consultant. Next to Marzi stands Selena Ahmed herself with Noah ten Broeck, chef and all around helper and facilitator.

 * Selena Ahmed, Uchenna Unachukwu, John Richard Stepp, Charles M. Peters, Chunlin Long, Edward Kennelly^.Pu-erh tea tasting in Yunnan, China: Correlation of drinkers’ perceptions to phytochemistry. Journal of Ethnopharmacology, Volume 132, Issue 1, 28 October 2010, Pages 176–185.

** Nicola Pirastu, et al. Association Analysis of Bitter Receptor Genes in Five Isolated Populations Identifies a Significant Correlation between TAS2R43 Variants and Coffee Liking. Published: March 19, 2014. http://dx.doi.org/10.1371/journal.pone.0092065.