Can what’s spicy "hot" cool you down?

In this time of iced tea, it is hard to imagine that drinking something spicy “hot,” say a deliciously spicy chai, could make you feel cooler, but that may well be the case!

Drinking plain cold water can cool you down,* in part because you will tend to drink more, and therefore have more capacity to sweat; in part because cold water or even better, icy slush, seems to cool down core body temperature by mechanisms still poorly understood**; and in part through the psychological/physiological process of feeling refreshed.*

So what does drinking something spicy do? As you know, when you eat a too hot chili pepper, you start to flush and break out in a sweat. The flush may make you feel hotter, but in fact what is doing is bringing blood the body surface where it helps to lose heat, both directly and by warming up the sweat and causing evaporation—this reaction to spice is the result of activating TRPV1, the hot receptor in the mouth and throat.***

So to get the best of both worlds: enjoy an ice cold spicy chai slush—the black tea and spices activate TRPV1 while the ice refreshes and cools you down!

For delightful instructions, see: http://www.indiansimmer.com/2014/06/indian-iced-masala-chai-recipe.html, Here's what it looks like:

* Tan, P. M. S. and Lee, J. K. W. (2015), The role of fluid temperature and form on endurance performance in the heat. Scandinavian Journal of Medicine & Science in Sports, 25: 39–51. doi: 10.1111/sms.12366.

** One mechanism may be that an increase in body water content may be able to take up more of the heat your body produces, with the water serving as a heat sink.

*** Narender R. Gavva et al. The Vanilloid Receptor TRPV1 Is Tonically Activated In Vivo and Involved in Body Temperature Regulation. The Journal of Neuroscience, 28 March 2007, 27(13): 3366-3374; doi: 10.1523/JNEUROSCI.4833-06.2007.

TAARs

You have heard of the classic type of odor receptor in the nose, the type that senses the aromas of flowers and fruit and so much else. Did you know that there is a second type of odorant receptor?

These receptors are called “TAARs,” which stands for Trace Amine-Associated Receptors. They have also been called Trace Amine Receptors (TAs or TARs), though the former appellation may be more appropriate because we do not know as yet the full repertoire of molecules that bind to these receptors. 

Their existence was first described in 2001, their discovery the result of searching for genes coding for proteins with certain characteristics.* In the case of the TAARs the characteristic in question is the ability to bind to amine compounds such as dopamine and amphetamine. 

Humans have 6 functional genes for TAARs and 3 pseudogenes (= genes that have changed enough through human evolution that they no longer produce functional proteins). Of the functional gene products, one (TAAR1) exists in multiple tissues but not the olfactory tissue, and the rest (TAAR 2, 5, 6, 8s, and 9) appear to exist only in olfactory tissue. These receptors can be found on cells similar in both structure and location to regular olfactory cells, and they send their messages through the olfactory bulbs, just like regular olfactory neurons.**

What message do these TAARs send?  “STENCH!!!”

As anyone who has experienced Icelandic hákarl—fermented shark—can tell you, the process of letting fish rot creates a distinct and utterly foul smell. The chemical that imparts this stench: trimethylamine; the receptor that responds to it: TAAR5. (According to Wikipedia, Chef Anthony Bourdain described kæstan hákarl as "the single worst, most disgusting and terrible tasting thing" he has ever eaten—and he has eaten plenty of disgusting things!)

Hákarl hanging to dry in Bjarnahöfn in 2005. Photo by Chris 73 (Wikimedia Commons). 

Other compounds that bind to human TAARs: 

• phenethylamine, which lends its power to the stench of carnivore urine; this compound induces fear in rodents and serves as a warning to humans that, say, a tiger is nearby—when tigers mark their territory with urine, phenethylamine provides much of the urine’s persistent and aversive odor.
• tyramine, which occurs in certain cheeses, chocolate, and red wine, and—I might add—pu-erh; its odor has been characterized as meaty and dirty, but also as sweet and vegetal.***
• N-methylpiperidine, which, as its name implies, occurs in pepper—I believe that it gives that slightly sour unpleasant smell to old ground pepper, though I cannot be certain.

The total number of compounds to which TAARs respond is not known. One can say, however, that many of the known compounds contribute significantly to urinaceous and rotting smells.

Interestingly, some humans have genetic variants of the TAARs that lead to inability to sense some of these smells.**** Lucky them—or perhaps not—I guess it depends on the circumstances!

* Borowsky B, et al. (2001). Trace amines: identification of a family of mammalian G protein-coupled receptors. PNAS 98 (16): 8966–71. doi:10.1073/pnas.151105198; Bunzow JR, et al. (2001). Amphetamine, 3,4-methylenedioxymethamphetamine, lysergic acid diethylamide, and metabolites of the catecholamine neurotransmitters are agonists of a rat trace amine receptor. Mol. Pharmacol. 60 (6): 1181–8. doi:10.1124/mol.60.6.1181. 

** Stephen D Liberles. Trace amine-associated receptors: ligands, neural circuits, and behaviors. Current Opinion in Neurobiology. Volume 34, October 2015, Pages 1–7.

*** “Our results showed that among 207 kinds of tea tested, Pu’er ripe tea contains the most kinds of and the highest content of the biogenic amines, followed by Pu’er sun dried tea, and Pu’er raw tea contains the least. The method should be helpful for the quantification of biogenic amines in the tea product and the tea quality control.” Mengying Zhang et al. Determination of Eight Different Biogenic Amines in Pu'er Tea by HPLC. Focusing on Modern Food Industry (FMFI) Volume 3, 2014 doi: 10.14355/fmfi.2014.03.009.

**** Vanti WB et al. Discovery of a null mutation in a human trace amine receptor gene. Genomics. 2003 Nov; 82(5):531-6.

Electronic noses

One of the big problems with using trained panelists for tea aroma evaluations lies in the variability of the human sense of smell, both between individuals and across time for any single individual. 

A solution to this problem would be to develop an electronic nose, which would be able to detect the different chemical constituents of a mixture of volatile chemicals that make up an aroma. The ideal electronic nose would be able to detect the individual voltiles, identify them, then tell you what the resulting combo of volatiles would smell like. An example of the latter problem: two quite different chemicals—ethyl isobutyrate, which has a sweet, fruity, slightly garlicky smell, and ethyl maltol,  which is sweet with a strawberry jam aroma—when put together together give a distinct pineapple aroma.

Existing electronic noses rely on the ability of volatiles to bind to electrodes coated with specific compounds that bind different categories of volatiles. Once the volatile is bound, a current can go through the electrode, resulting in a signal that a detector can recognize. So far these “noses” are not able to perform the tasks listed above, but they can detect differences among different samples, or detect certain individual volatiles that may be indicative of the quality of a tea.

All if this by way of introduction to a paper from Italy about the comparison between volatiles in the processed leaf and ones in the cup among a sampling of Chinese teas.* Here I am going to mention one observation (among many) that I find quite fascinating, and that confirmed what I have thought might be the case for a long time, namely that oolong and white tea were more alike than you might believe when you just consider the processing of each.

The white was a Pai Mu Tan, consisting of a leaf bud and two youngest leaves (W in the graph below). The oolong was a Wuyi Shui Xian, second and third leaves from the top (O in the graph below). The other teas were greens (G), black (B), yellow (Y), and pu-erh (P).

The graphs are designed to show the patterns of volatiles in each of the teas, using a statistical technique called principal component analysis. I’ve circled in red the white and the oolong—the left panel represents the volatiles emanating from the leaf and the right panel the volatiles emanating from the infusion.

While there are obvious differences between leaf and infusion, the white and the oolong teas cluster together in each graph, suggesting that the pattern of volatiles in them is similar.

These similarities, as Torri and her colleagues suggest, are probably due to the long withering process each type of tea undergoes. This allows the leaf to produce all the injury chemicals that we find so delicious!

The typical suggestion is that white tea is ultra delicate, which it may be, but the richness of volatiles that the long withering creates makes the delicacy extremely complex. You often see white tea matched with cucumber or mint. Yes, the volatiles in white tea do activate the cold receptors, so cucumber or mint might seem to be a good match. But the compounds in cucumber and mint are so dominant you lose the wonderful complexity of the tea. 

A better suggestion? perhaps a lightly lemoned pound cake? Let me know what you think. 

* Torri, L., Rinaldi, M. and Chiavaro, E. (2014), Electronic nose evaluation of volatile emission of Chinese teas: from leaves to infusions. Int J Food Sci Technol, 49: 1315–1323. doi:10.1111/ijfs.12429.

=> Red, White, and Blue Cheese Blueberry Brown Betty for Chinese Green Tea <=

Last 5th of July, I posted this recipe on Facebook, a day late for the 4th of July celebrations here in the US. I've posted it early this year, so that those of you who want to get prepared will have time!

Here's a very special way to use the blueberries that are in season now! This dessert goes delectably with a Chinese green tea—refreshing yet with slightly toasty flavors.
The blueberry, lemon, and blue cheese flavors hit the cool "green" receptors, as does the tea, while the whole wheat breadcrumbs, the cinnamon, and the tea's slightly brown side, aim for the warmer receptors, making for a complex concert of flavors that linger happily on the tongue. BTW, the saltiness of the cheese takes away any bitterness in the tea. Here goes!
Ingredients:
2 pints (about 1 liter) fresh blueberries
1.5 cups (350 ml) white sugar
Juice of 1 lemon
2 teaspoons (10 ml) true cinnamon
5 oz. (about 150g) mild blue cheese (can also be 6 oz. - depends on the size of the package you can get)
8 oz. breadcrumbs (about 250 ml) (I used whole wheat panko - think regular breadcrumbs may be a better choice - the butter will soak in better)
1/4 lb (one stick) (about 110g) butter
Method: Preheat oven to 400ºF/200ºC.*
In a colander, wash the blueberries. Be sure to carefully look for and remove stems and any berry that has seen better days. Drain and put in a bowl. Add sugar, cinnamon, and lemon, mix, and set aside. (if you are tempted to taste a berry at this point, by all means give in: the berries will taste sweet and cool and fresh, with the slight and slightly delayed tang of the cinnamon to cap the experience! I confess to tasting several...).
In another bowl, combine the bread crumbs and crumbled blue cheese (as crumbled as possible). Melt half of the butter, and drizzle over the cheese-bread combo, and mix well.
Layer the bread-cheese combo in a well-buttered 2 quart dish, followed by a layer of the blueberries, then top with another layer of the bread-cheese combo. Cover (I covered my dish with foil) and put in the over for 20 minutes. Remove from oven, remove cover, dot generously with remaining butter, and place back in the oven uncovered for another 5 to 8 minutes to brown a little. When it looks good to you, remove again, let cool, and then refrigerate overnight. Enjoy the next day with the Chinese Green Tea. Some people might like whipped cream on the betty,** but I think it diminishes the complexity of the flavors.

Top: Red, white, and blue - berries, sugar, and cinnamon before the addition of lemon juice; bottom: the finished product with tea (yes, it crumbles when you serve it, mixing all the flavors together)
------
* Metric conversions are approximate, so use your own judgment! If it looks good and tastes good, then you've got it right! Please send me any corrections!!

** Something to do in your spare time: look up the differences among brown betties, cobblers, crisps, crumbles, grunts, slumps, buckles, etc. — I've called this dessert a brown betty, but it may not be, depending on the definition. In the old book on which this recipe is based, it's called a grunt, but I'm not sure that's correct either.

Thoughts about yogurt

Yesterday I enjoyed a great meal at our local Turkish restaurant, Istanbul.  We enjoyed our lentil soup (kirmizi mercibek corbasi) with cacik, their homemade Turkish yogurt with fresh parsley, cucumbers and garlic. The lentil soup is pretty spicy, so my daughter and I add lemon and then fold in cacik, to give an absolutely delectable combination, with just the right amount of heat. (Yes, I have to sip the soup repeatedly as I add cacik to get the level just right!)

Lentil soup at Istanbul Restaurant, Ithaca NY.

What is the yogurt doing for this combination?

First, the parsley, cucumbers and garlic, as well as the lemon, activate the cold receptors—this activation helps to dampen the activity of the hot receptors, so the overall heat is just right. 

Second, I was wondering about the fat in their yogurt (which, incidentally, is not very creamy, unlike the Greek yogurt you can buy around here). Technically, fat also helps turn off the hot receptor TRPV1, but yogurt’s sourness/acidity should turn that receptor on. When tasted by itself, this restaurant’s yogurt isn’t particularly sour—maybe the parsley/cucumber/garlic, by turning off TRPV1 are cutting some of the sourness as well. But did fattiness contribute to the decrease in heat?

My attempt to answer this question led me into the maze of literature—most of it fairly old actually—on the sensory properties of yogurts with different percentages of fat.

Not only can yogurt contain varying amounts of fat, it can also contain varying amount of sugar, and dairy proteins, all of which could influence sourness, as of course differences in lactic acid concentration, and citric acid concentration as well. Further, lactic acid has a bitter taste for some people, which may also influence the perception of sour. The result is a complex of taste receptor and trigeminal interactions that are, at least at first blush, difficult to parse.

As described in the most recent paper I could find on the subject, trained panels evaluated the sensory characteristics of a number of commercial yogurts. The panelists learned to recognize the 

different possible flavors by tasting solutions with characteristics flavors. 

(One example that I, having had children and grandchildren, particularly appreciated is contained in Table 2 of this article:

Butyric

An aromatic that is sour and cheesy, reminiscent of baby vomit

DiGiorno Grated Romano Cheese = 6.0 (aroma) DiGiorno Grated Romano Cheese = 9.0 (flavor) Butyric acid (character reference)

The numbers are indicative of the panelists’  perception of intensity.)

All in all, the authors tested for 25 flavor/taste characteristics and 10 texture, mouthfeel, and mouthcoating attributes.

The correlations among the flavor characteristics were particularly instructive. For example,

“overall sour, lactic, and sour taste were significantly correlated to sharp/bite flavor. Sharp/bite comprises of sour, astringent, and pungent impressions, thus this correlation was understandable.”**

These correlations are all the more understandable if you know that sour, astringent and sharp/bite are all produced by activation of TRPV1. Although I prefer to reserve the word “pungent” for chemicals that activate the cold receptor TRPA1, such as wasabi, this confusion is also understandable as well, as both sharpness and pungency refer to the pain caused by activation of either of these receptors.

But back to fat: overall it is hard to find evidence that the fat in yogurt modifies sourness or sweetness. 

In the Brown/Chambers paper, there is no strong correlation between fattiness and sourness or sweetness. Earlier studies seem to indicate either no effect or dampening of sourness by fat. 

One study may give us insight into why there are such differences: the authors of this study did not lump all the panelists together, but looked at the effect of individual differences on the relationship between sourness and fattiness. These individual differences turn out to be critical, as some people found no effect and others sis. This research described in this paper was done long before we had DNA analysis, so we cannot say for certainty that these individual differences in perception were caused by individual differences in the gene for TRPV1 or its expression. However, it seems to me that this may be the cause. The genetics of TRPV1 in humans are extremely complex, with possibilities for both gain and loss of function, so that one may readily expect huge variation in response.****

In any case, this particular yogurt from Istanbul restaurant is not very sour to me, but whether it is the cold receptor activators (parsley, cucumber, and garlic) or the fattiness, I cannot say.

* Marissa D. Brown, Delores H. Chambers. Sensory Characteristics and Comparison of Commercial Plain Yogurts and 2 New Production Sample Options. Journal of Food Science. Volume 80, Issue 12, pages S2957–S2969, December 2015.

** Grammar as in the text.

*** H. Tuorila, et al. Sensory attributes and acceptance of sucrose and fat in strawberry yoghurts. International Journal of Food Science and Technology (1993) 28, 359-369.

**** Ruslan Dorfman, Hubert Tsui, Michael W. Salter, and H.-Michael Dosch. TRPV1 GENETICS.  In Vanilloid Receptor TRPV1 in Drug Discovery, Gomtsyan, Arthur and Faltynek, Connie R (eds.) ISBN 9780470175576, pp. 134 - 149.

Some more about smell…

At World Tea Expo 2016 I presented the following graph about smell, which shows where in the brain our awareness of smell is put together:

Odorants come into the nose either through the nostrils (orthonasal) or through the back of the throat (retronasal). There they are captured by receptors in the endings (dendrites) of nerve cells poking through the olfactory epithelium (marked 4 in the diagram) at the roof of the nose. The bodies of these nerve cells (6) are interspersed among the cells of the olfactory epithelium, while a long extension of each (the axon) makes its way through small holes the skull (3) to reach the olfactory bulb (1). Ends of groups of axons gather together to form glomeruli (5), and together they contact mitral cells (2) in the olfactory bulb. 

Image:Brain human sagittal section.svg Image:Head lateral mouth anatomy.jpg by Patrick J. Lynch, medical illustrator

The ratio of axons to mitral cells is approximately 1000 to 1, so you can see that the mitral cells are in a position to calculate how much odorant is coming through: the greater the number of receptor cells activated the more likely it is that the mitral cell will be triggered and the stronger the signal sent to the  brain.

At the same time, the fact that the mitral cells each receive messages from at least a thousand receptor cells means that the mitral cells are in a position to simplify the message to be sent to the brain. in order to extract a specific message from the huge number of possible odorant signals the mitral cells interact among themselves and among other cells in the olfactory bulb, activating some and inhibiting others. The net effect is a “sparse” message that is then sent on to the pyriform cortex.

The pyriform cortex takes the message and, before contacting the next set of brain structures, assembles the input into “odor objects.” For example a group of smells may be characterized by the pyriform cortex as minty or citrusy. The more sensitive you are to a group of odors, the more likely you are to assemble them into these objects (configural representation), and the less likely you are to perceive them as separate elemental odors.*

The pyriform cortex next sends on its analysis to several different parts of the brain, as shown in the box in the diagram above. Ultimately the message arrives in the orbitofrontal cortex right above the eyes, where the odor’s identity is finally brought into awareness, and its importance and valence (either pleasant or unpleasant) evaluated.

As you can see in the diagram, the superior frontal cortex may also get into the act. Its activation depends on whether the the odor is hedrnically simple or complex. What does this mean? Some aromas are either pleasant or unpleasant, in other words hedrnically simple. By contrast some aromas are hedonically complex, because they have both pleasant and unpleasant components. The aroma of oolongs is one such type of aroma: it contains a number of pleasant odorants in the jasmine family, but it also contains a considerable amount of indole, which is also found (for example) in fecal material—stinky, in other words. When we encounter hedonically complex smells, the superior frontal cortex sends the message: sit up and take notice! 

BTW, that’s why the best perfumes aways contain a less-than-pleasant component (such as indole): it makes a person pay more attention to the person wearing the perfume!

* Thierry Thomas-Danguin et al. The perception of odor objects in everyday life: a review on the processing of odor mixtures. Frontiers in Psychology. June 2014 | Volume 5 | Article 504 ; doi: 10.3389/fpsyg.2014.00504 

** Fabian Grabenhorst, Edmund T. Rolls, Christian Margot. A hedonically complex odor mixture produces an attentional capture effect in the brain. NeuroImage 55 (2011) 832–843.

What percentage of flavor is smell?

You may have heard people say that “taste” is really something like 80% smell. At our World Tea Expo 2016 workshop I was asked whether this were a fact.

The truth is that we can’t do such a calculation. The purposes of taste and smell are quite different from each other: taste gives us the nutritional value of an ingesting, while smell allows us to know what it is we are ingesting. Together with trigeminal sensation which serves as a sort of volume dial, each makes a necessary contribution to flavor. One modality without the others simply can’t lead to the full perception of flavor.

I think that the reason why this notion of percentage comes up is that the effect of holding one’s nose when tasting something is quite astonishing. Suddenly you lose the full richness of a flavor, to have it rush back once you let go.

It is much harder to “hold” your tongue the way you can hold your nose, so we don’t have an everyday way to experience the loss of taste. Still, loss of taste buds means loss of flavor as surely as does loss of smell. As a physician I have been with many a patient who has lost his or her taste buds—whose tongue, due to chemotherapy for example, is devoid of taste papillae. Patients with this condition complain that food has no flavor and that food aromas, when sniffed, are dampened and often unpleasant.

Taste, smell, and trigeminal sensations are only three of the peripheral sensory inputs that influence flavor. Vision and hearing also contribute, and you will get more flavor from a food if you are hungry than if you are sated, so the internal state of the body is also figured in. We also consciously or unconsciously compare our memories and expectations with the information given by our senses to determine how flavorful something is. 

In other words, what we experience as flavor is the product of the brain’s analysis of all manner of inputs, and its attribution of flavor to sensations coming from the mouth. That’s why it’s impossible to parse the sources of flavor in terms of percentages.