Tea and Chocolate Pairing?

Pairing teas with chocolate is a difficult proposition, and becoming more so every day. The proliferation of chocolate origins, not to mention the multitude of ways that a given chocolate bean can be treated, can make your head spin! Add to that the equal plethora of teas…how does a person decide? Do we have to resort to trial and error? When high quality chocolate is now coming in at $8 or more a bar, mistakes can become quite expensive!

Pairteas has been devoting some thought to this question, the more so because we (my friend Marzi Pecen and I) may be presenting tea and chocolate pairings at World Tea Expo next year.  Marzi has training as a perfumer—you may have experienced her expertise at our workshop on oolongs at World Tea Expo this past June. (In this case, “our” consists of Donna Fellman, Marzi and I). So one aspect of pairing will be to understand the aromatic components in chocolate and teas, and how they interact.

An example of two chemicals in both tea and chocolate that differ among chocolates of different origin, and differ among teas as well: linalool and phenyl acetaldehyde. The chromatograph below shows the difference in concentration of each of these compounds in the Venezuelan (top) versus the Ghanaian (bottom) chocolate, with linalool concentration at the green arrow, and phenyl acetaldehyde at the purple.* [Note that this is just one study—the study of chocolate aroma compounds (volatiles) is really in its early days, so whether my conclusions apply across the board is subject to the results of further study.]

If you just look at the peaks, they seem to be roughly the same size, but in fact they are not. The red arrow shows the internal standard—it’s what you should use to compare the size of the peaks. The Venezuelan chocolate’s internal standard is quite tall compared to that of the Ghanaian, so the levels of linalool are actually quite low compared to the levels in the Ghanaian. The same is true for phenyl acetaldehyde.

So what does this mean for pairing with these particular chocolates? 

Linalool has a citrus, floral, sweet, bois de rose, woody green, blueberry aroma, and binds to the cool/cold receptors (http://www.thegoodscentscompany.com/data/rw1007872.html#toorgano). It is abundant in all teas, but it stands out in green teas, so as a guess you will find that this Ghanaian chocolate will pair better with green tea than other chocolates.  

At WTE this past June we sniffed phenyl acetaldehyde—it activates the warm receptors—and discovered that Bai Hao has quite an abundance of this aroma. It's described as “honey, floral rose, sweet, powdery, fermented, chocolate with a slight earthy nuance” (http://www.thegoodscentscompany.com/data/rw1009932.html#toorgano). Again, oolongs will probably go better with this Ghanaian chocolate than with this Venezuelan, given that the peak is higher.

So what will go better with this Venezuelan chocolate? That will be the subject of another blogpost—and more experiments!

* A. Cambrai, C. Marcic, S. Morville, P. Sae Houer, F. Bindler, E. Marchioni. Differentiation of chocolates according to the cocoa's geographical origin using chemometrics. Journal of Agricultural and Food Chemistry, 58 (3) (2010), pp. 1478–1483.

Cork taint, odor suppression, and tea.

Was just listening to poet Trish Perlman interview a local wine wine consultant Dave Pohl, when they discussed cork and cork taint.* This discussion led me to look back at 2,4,6-trichloroanisole (TCA), the chemical responsible for cork taint. When I say “look back” I mean that I had tasted wine with cork taint during a class in the chemistry of wine sensory perceptions that I took at Cornell a few years ago. It struck me a pretty unpleasant—moldy, like wet newspaper.

So I decided to look for more info about TCA, and the first paper I found was quite a surprise. Takeuchi and her colleagues found that instead of actually having its own odor at very low concentrations, TCA actually suppresses our ability to sense other odors!** It didn’t work by affecting the odorant receptors directly, but by decreasing the function of the next step in odor perception, after an odorant binds to its receptor. This step involves the opening of channels that allow calcium to enter the receptor’s cell. When calcium enters the cell, the cell then passes the odorant message to the rest of the olfactory system. When these channels, called  cyclic nucleotide-gated (CNG) channels are suppressed, no message can be sent. According to Takeuchi and her colleagues, “TCA exerted a much more potent suppressive effect on CNG channels (100–1,000-fold) than other known olfactory masking agents that have been widely used in perfumery.” And the effect occurs at concentrations as low as 600,000 molecules of TCA in about 3x10^25 molecules of water (that’s 10 with 25 zeros after it! It’s also about one liter of water). Talk about a needle in a haystack!

This experiment was done in the petri dish. What about odor suppression in actual people? At what concentration does it make wine samples have less odor? At concentrations of parts per trillion. And the threshold for smelling TCA itself? 30 parts per million! 

Conclusion: even the tiniest amount of TCA can decrease the aroma of a wine, even when you don’t get off-flavors.

So where does TCA come from? It is a metabolite made by fungi from a pervasive environmental contaminant, 2,4,6-trichlorophenol. This compound is considered to be highly carcinogenic, whereas the metabolite TCA is not, so some consider the fungal transformation of TCP to TCA to be beneficial for the environment, even when it makes your wine less attractive. (Incidentally, TCA binds easily to polyethylene, so you just need your wine to make contact with some plastic wrap for a few minutes to remove the TCA***)

And, seeing that this blog is mainly about tea, with occasional excursions into discussions of wine, what about TCA in water and tea? Takeuchi and her colleagues tested green tea and tap water, as well as a number of other foodstuffs, and there it was. They found it in green tea at 5 parts per trillion, enough to suppress aromas without giving a smell of its own. As they say: “It thus seems likely that TCA degrades the olfactory quality not only of wines, but also of a wide variety of foods and beverages that have not yet been well investigated.”

Maybe we should think about drinking our green tea, or even more importantly our pu-erh, from plastic cups…

* http://outofboundsradioshow.com/shows/

** Hiroko Takeuchi, Hiroyuki Kato, and Takashi Kurahashi. 2,4,6-Trichloroanisole is a potent suppressor of olfactory signal transduction. PNAS | October 1, 2013 | vol. 110 | no. 40 | 16235–16240.

*** https://en.wikipedia.org/wiki/Cork_taint

Bitter and sweet and grapefruit

As you may have noticed, I’ve been very interested in the genetics of bitterness and sweetness, and in the masking effects of bitterness on sweet and vice versa. One interesting result comes from a study of the genetics of perceived bitterness of common beverages, by Valerie B. Duffy and her colleagues.•

While the study also addresses the bitterness of alcohol and espresso coffee, what caught my eye today was the discussion concerning grapefruit juice. 

I don’t eat grapefruit or drink grapefruit juice for reasons other than not liking it—it affects the metabolism of a number of medications, none of which I am on but which I could potentially be on, for example coumadin—but I do find it bitter, and not sweet, and I don't like it.

Turns out that I have the gene changes that correspond to “Het” in the diagram below, from the article. As you know, proteins are made from amino acids strung together in a chain. The code for indicating which amino acid goes where is in your DNA. Single changes in the code can make for different amino acids in the protein, which makes the protein work less well, or even not at all.

Some people have only the amino acid cysteine at position 299 in protein chain that makes up their bitter receptor TAS2R19, and are indicated as Cys299 in the graph—both parents gave them the DNA code that gives this version of the protein. Some people have only the amino acid arginine at that position, because they inherited that version of the DNA from both of their parents—they are indicated as Arg299 in the graph. Arginine at position 299 makes for a less effective receptor, so they don’t find grapefruit juice bitter. As it turns out they tend to find it sweet instead, and like it much more than do the people who have the code for cysteine at position 299.

As for me, “Het” stands for heterozygote, which means that I inherited one version of the DNA from my mother, so I make half my proteins with the arginine at position 299, and one version from my father, so I make the other half of the proteins with cysteine at position 299. (I know which parent gave me which variant because my mother adored grapefruit, and my father thought it was way too bitter, and didn’t like it at all.)

What interested me as a heterozygote is that I never have found grapefruit to be sweet, and when I had to eat it as a child I heaped sugar on it to make it bearable. As you can see from the graph, there is no real difference between Cys299 and Het in liking—that’s what is meant by p=.115—whereas there is a large difference between Cys299 and Arg 299 (the lower the p value the greater the difference), and some difference between Het and Arg299. 

What is not marked on the graph, and what intrigued me is the possible consequence of a difference in sweetness perception in conjunction with bitterness perception. In other words, for the hertozygotes, is it the combination of a slight increase in bitterness perception coupled with a slight decrease in sweet perception that makes for a greater dislike?

And another question: is there a competition between bitterness and sweetness, so that people who have at least one copy of the more effective receptor (like me) may not perceive the bitterness as strongly, but it is sufficiently strong to dampen the sweetness of the grapefruit, and to make it less delicious.

* Hayes JE, Wallace MR, Knopik VS, Herbstman DM, Bartoshuk LM, Duffy VB. Allelic Variation in TAS2R Bitter Receptor Genes Associates with Variation in Sensations from and Ingestive Behaviors toward Common Bitter Beverages in Adults. Chemical Senses. 2011;36(3):311-319. doi:10.1093/chemse/bjq132.

Dolphins don’t worry about pairing, but can fish smell?

Have you seen the ad for Snapple, where a dolphin decked out in pearls and furs tries to smell a perfume at a department store, and fails; then inside the Snapple cap you read that dolphins can’t smell?

Indeed, some Cetaceans, including dolphins, porpoises, and toothed whales, can’t smell much if anything because the genes that would normally code for odor receptors (ORs) have substitutions that make for nonfunctioning receptors for over some 95% of them. Furthermore, they lack an olfactory bulb.

Which led me to wonder, can fish smell? or is it in the nature of the water environment to make smelling unnecessary?

To explore the answer to this question, I searched for an article on fish odorant receptors, and found a very thorough study by Alioto and Ngai comparing fish genomes to mouse genomes, which gives strong clues concerning the evolution of our odorant receptors and those of Cetaceans.*

ORs were created in our vertebrate genomes through gene duplication, starting with the gene for melanocortin receptors. Melanocortins are hormones, all derived from slicing of a larger protein, proopiomelanocortin, in the brain and other tissues. As the name suggests, melanocortins are involved with functions as divergent as skin pigmentation and corticosteroid production, and also in appetite and satiety. 

Genes normally duplicate in the course of evolution. Over time the duplicates accumulate mutations, which change their functions; these mutated duplicates may in turn duplicate again and accumulate mutations. This process of duplication and mutation leads to the development of families of genes.

It turns out that families of ORs appear to have been present from the earliest development of vertebrates. According to Alioto and Ngai, lampreys have OR genes in two families, both of which are closer in sequence to the ancestral melanocortin receptor gene, and therefore more “primitive.” Zebrafish have somewhere between 6 and 8 families of OR genes, which (in theory at least) should enable them to sense a wider repertoire of scents than mice or humans, who only have 2 families.  However, we have a larger number of different sequences than do fish, about 1000 versus about 100 in fish, which may allow us to make finer differentiation among smells. It is thanks to this refinement within families that we can detect the difference between heptanal with its herbal note and octanal with its orange citrus note—these two compounds differ only by one carbon atom with its two hydrogens. 

This image, from http://www.nature.com/ng/journal/v45/n4/fig_tab/ng.2568_F1.html, shows the evolutionary relationships among lampreys, ray-finned fish including the zebrafish, and mammals.

So why did toothed Cetaceans lose their capacity to smell? It can be argued that it is because their nose is no longer in front of them. If you look at the fossil ancestors of Cetaceans, you will see that the nose moves progressively to the top of the head, where it is now, in the form of a blowhole. Blowholes are closed when they are under water, so any sniffing capacity would be useless there. 

The evolutionary tree of whales and porpoises. Note the position of the nasal opening, which is right in the middle of the top of the skull at the end of the evolution.

From http://phenomena.nationalgeographic.com/2014/03/12/seeing-the-ocean-with-a-buzzing-nose-2/

Baleen whales (aka Mysticetes) also have blowholes, but they do have olfactory bulbs and a set of ORs, about 51% of which appear to be functional, and all of which belong to only one of the two mammalian classes—they seem to have lost the other. Furthermore, their olfactory bulb represents 0.13% of their brain weight compared to 0.0008% of our brain weight. (Incidentally we also have about 50% of our ORs in the form of non-functional pseudogenes.) So their repertoire of scents is perhaps limited to one type, but definitely present.

The reason for the difference may lie in the way the two classes of cetaceans hunt prey. The toothed whales do so by echolocation—no sense of smell needed. By contrast, baleen whales need to find schools of krill, which do not give a distinct pattern with echolocation, but may emit specific scents.

* Tyler S Alioto and John Ngai. The odorant receptor repertoire of teleost fish. BMC Genomics, 2005, 6:173; DOI: 10.1186/1471-2164-6-173. 

** http://www.north-slope.org/assets/images/uploads/Thewissen%20et%20al%202011-MarMammSci-bowhead%20olfaction.pdf

Origin of the Camellia sinensis plant

Have been intrigued by the question of where the tea plant originated, so have been exploring the available papers on the subject. There are two basic science-based (as against expertise-based) approaches to this question. One is to look at the biochemistry of the tea leaves, and the other is to look at tea plant DNA. 

With respect to the the first approach, found a fascinating study that compared polyphenol content among 89 wild, hybrid, and cultivated tea trees.* It turns out that you can derive a “family tree” showing the relationships among tea tree lines using the relative amounts of (-)-epigallocatechin 3-O-gallate (EGCG), (􏰀-)-epigallocatechin (EGC), (-􏰀)-epicatechin 3-O-gallate (ECG), and (-􏰀)-epicatechin (EC).  The older lines of plants have less of the first two polyphenols and more of the the third and fourth. This analysis led to the conclusion that “the Puer City and Xishuangbanna [in Yunnan] districts are among the original sites of tea tree species.”

With respect to the second approach, there have been a number of DNA studies. A micro satellite study of 392 tea samples pointed to the strong possibility that the tea tree was domesticated three different times, yielding the Camellia sinensis var. sinensis on the one hand, and Camellia sinensis var. assamica from China and Camellia sinensis var. assamica from India on the other.** These differences were evidenced by three different micro satellite patterns. A microsatellite is a stretch of DNA made up of a repeated pattern of (usually) 2 to 5 bases. An example would be TATATATA where T is the base thymine and A is the base adenine. Microsatellites are common throughout genomes of living beings, and are subject to a high mutation rate. That is why they are used for tracing lineages. 

If you look at the diagram below, from this study, which shows how all the tested plants are related, you will notice a first split between the Camellia sinensis var. sinensis, and the two var. assamica. According to those authors, the Chinese var. assamica originally developed in Yunnan as well. 

This diagram, from **, shows the three different genetic patterns of Camellia sinensis. The length of the lines represents the genetic distance from the original plant. The pink lines among the green represent Camellia sinensis var, sinensis growing in India. Note that the Indian var. assamica is closer to the putative original plant, differentiated in Yunnan into the Indian and Chinese versions, and then somehow migrated to India, where it became an isolate. 

A further look at the genetic diversity among wild trees point to Yunnan as the origin of the Camellia sinensis var. sinensis: this province shows the greatest genetic diversity among the wild trees—the longer a species  is present in an area the greater the chance to accumulate mutations, and the greater the differences among individuals of the present day populations.***

These data all suggest that Yunnan was the center of the evolution of Camellia sinensis, and that its variants in all their glory spread from there. 

 *Jia-Hua Li, Atsushi Nesumi, Keiichi Shimizu, Yusuke Sakata, Ming-Zhi Liang, Qing-Yuan He, Hong-Jie Zhou, Fumio Hashimoto, Chemosystematics of tea trees based on tea leaf polyphenols as phenetic markers, Phytochemistry, Volume 71, Issues 11–12, August 2010, Pages 1342-1349, ISSN 0031-9422, http://dx.doi.org/10.1016/j.phytochem.2010.05.002.

** M. K. Meegahakumbura, M. C. Wambulwa, K. K. Thapa, M. M. Li, M. Möller, J. C. Xu, J. B. Yang, B. Y. Liu, S. Ranjitkar, J. Liu, D. Z. Li, L. M. Gao. Indications for Three Independent Domestication Events for the Tea Plant (Camellia sinensis (L.) O. Kuntze) and New Insights into the Origin of Tea Germplasm in China and India Revealed by Nuclear Microsatellites. PLOSone. Published: May 24, 2016. http://dx.doi.org/10.1371/journal.pone.0155369.

*** Liu, B., Sun, X., Wang, Y., Li, Y., Cheng, H., Xiong, C., & Wang, P. (2012). Genetic diversity and molecular discrimination of wild tea plants from Yunnan province based on inter-simple sequence repeats (ISSR) markers. African Journal of Biotechnology, 11(53), 11566-11574.

Yao, M., Ma, C., Qiao, T. et al. Diversity distribution and population structure of tea germplasms in China revealed by EST-SSR markers. Tree Genetics & Genomes (2012) 8: 205. doi:10.1007/s11295-011-0433-z.

Turkish tea

I am exceptionally fond of the tea served at our local Turkish restaurant, Istanbul Turkish Kitchen, here in Ithaca New York. I am exceptionally fond of their food, too, but as this is a blog mainly about tea, I’ll concentrate on the tea.

Turkish tea at Istanbul Turkish Kitchen, Ithaca, New York (http://istanbulithaca.com).

Turkey developed its tea growing capacity with the fall of the Ottoman Empire, in order to replace coffee that had to be imported. It’s grown in Rize Province, near the bend of the eastern Black Sea coast.  Rize has that warm moist climate that makes tea plants happy.

Tea (çay) gardens near Rize, Rize province, Turkey. Photo by User:Wikimol, from Wikipedia.

Was fascinated to read in Wikipedia that Turkey has the highest per capita consumption of tea in the world, “at 2.5 kg per person—followed by the United Kingdom (2.1 kg per person).” 

As for the tea that I had the other day: it was honey-sweet, roasted, and malty, warm-flavored, and delicately rose-like, with no trace of either bitterness or astringency. I was led to investigate what is known about the composition of Turkish tea that would give this unique (sorry for the over-used word!) flavor, so different from most other black teas.

As it turns out, I found one article* with the details that explains why the tea has this flavor. First, the warmth of the flavor was probably due to the lack of linalool, as much as to the presence of other compounds. This compound is found in all the other black teas I have tasted, and gives other black teas a slightly citrusy, flowery (it’s part of the cool scent of roses), and somewhat cooler taste, because it binds primarily to the cool receptors (TRPM8). According to the article, two “cold” compounds are abundant in Turkish tea: (Z)-2-penten-1-ol with its horseradish /mustard quality, and (Z)-2-hexen-1-ol, which has a green vegetative note. These might have imparted some fresh coolness to the tea, but I certainly didn’t detect them. 

While lack of linalool would shift the flavor to the warmer side of the spectrum, other compounds reinforce the warmth. In particular, benzyl alcohol has a warm sweet odor with a distinctly roasted quality. No doubt it was present in abundance in the tea I sampled. The same goes for benzaldehyde, with its sweet cherry-like odor. Note that benzaldehyde also has an almond quality, but I didn’t sense any of that in the tea: cherry yes, almond no. Finally linalool oxides with their floral qualities were probably present in the tea I tasted, and also among the compounds Alasalvar and colleagues found.

Three other compounds with a malty odor and flavor were found to be abundant in Turkish tea, namely 2-methyl propanal and 2- and 3-methyl butanal. I would be very surprised if they weren’t a significant component of the delicious flavor I experienced. Similarly, there are a number of other chemicals in Turkish tea which confer a roasty quality that no doubt were in the tea I enjoyed so much.

The one other chemical that I would have expected and was missing—in addition to linalool—was methyl salicylate. That sweet wintergreen compound has been detected in oolongs and particularly in black teas, but wasn’t on the list of the compounds in the Turkish black tea. I didn’t smell or taste it either. Plants make it as an insect repellent and as a warning compound to other plants about the presence of viruses.

I wonder why it isn’t there. 

* Cesarettin Alasalvar, Bahar Topal,Arda Serpen, Banu Bahar, Ebru Pelvan, and Vural Gökmen. Flavor Characteristics of Seven Grades of Black Tea Produced in Turkey. J. Agric. Food Chem., 2012, 60 (25), pp 6323–6332; DOI: 10.1021/jf301498p