Thursday, April 27, 2017

How much theanine in your cup?

When I was looking for information to share with you all at World Tea Expo come June, found a fascinating paper about L-theanine content of different teas available in England. L-theanine is a compound found in young tea leaves that may (or may not) have worthwhile effects on your mood and sleep.*

You may have heard that green tea has more L-theanine than does black tea. However, as the authors indicate, the studies providing these measures extracted total theanine from the leaf—they didn't measure the amount of L-theanine that gets into the cup you actually drink.

That's why the authors of the paper measured extracted L-theanine, namely the amount in a cup of 200ml, with the tea brewed with water at 80ºC for 2 minutes.

Under these circumstances the results were reversed, as the graph below shows. For the sake of simplicity, all of the teas I included in the graph were Twinings teas—several other brands of teas were tested, with the same results. 

Average theanine content of different Twining's teas.


The "Everyday" tea was a bag tea, while all the rest were loose leaf. The first difference is that the loose leaf teas released significantly less theanine than the bagged tea. The second difference is that the green and white teas released less than some, but not all, of the Twinings black teas. 

When all of the teas tested (including teas produced by other companies) were taken together, however, black bagged teas released significantly more theanine than did the loose leaf black teas and the loose leaf green and white teas. It is likely that the leaf particles in bagged teas offer more surface area to the water for extraction. With respect to the difference between some black teas and other teas, the difference may come from the more extensive processing of black teas, which may release more theanine.

Incidentally, for most of these teas, the maximum theanine was released at 2 minutes of brewing; and lemon, sugar, or small amounts of milk had no effect on theanine release.

Bottom line: enjoy your specialty loose leaf teas for their exquisite flavor, but if you just need a theanine "hit," go for a bagged tea!


* Emma K. Keenan, Mike D.A. Finnie, Paul S. Jones, Peter J. Rogers, Caroline M. Priestley. How much theanine in a cup of tea? Effects of tea type and method of preparation. Food Chemistry 125 (2011) 588–594.
 
 


Wednesday, April 19, 2017

Mango green tea and dirty socks

The other day, friend of Pairteas and tea connoisseur Marzi Pecen (www.pecen.net) asked me why her mango-flavored green tea had a smell of dirty socks, and why she couldn't taste the mango at all. Here's the (longish) answer — it has to do with the odorants in dried mango and how they interact with those in green tea.

First, what is the difference in odor profile between fresh and dried mango? 

Mango is highly perishable when fresh. By contrast dried mango is quite stable, and can readily be added to tea to create a flavorful blend. 

When I smell or taste dried mango by itself, I get a two step effect. The first effect is cool and slightly lemony, then a warm orange-like tropical fruit aspect quickly kicks in.

This two step effect can be explained from the data obtained by Bonneau and her colleagues, in which they compared fresh and dried versions of the most commonly cultivated mango, Mangifera indica L. cv. Kent.*

Fresh and dried mangoes differ dramatically in their aroma chemistry, though two compounds present in both fresh and dried mangoes — β-myrcene and 3-methylbutyl butanoate — together contribute strongly to the "mango" sensation.  Both of these compounds activate warm receptors.

The lemony sensation from dried mangoes comes from the presence of limonene and a small number of other terpenes with a citrusy flavor. Limonene in particular activates the cold receptor, which is why the first fleeting sensation is cool — cool receptors turn on quickly and turn off quickly, especially when turned off through activation of warm receptors, including sweet receptors. 

That's why the sensations quickly becomes warm: the "mango" compounds start activating the slow-responding warm receptors, and the flavor becomes intensely mango-y.

Next, what happens when you add dried mango to green tea?

Here's where we run into flavor problems! The process of drying mangoes leads to the production of hexanal and heptanal, and the disappearance of mesifuran. Hexanal and heptanal both activate the cool/cold receptors, while mesifuran is a major contributor to the sweetness and warm flavor of fresh mangoes. 

When dried mango is added to green tea (which itself activates cool/cold receptors) the balance of flavors shifts from warm to cool/cold. As a consequence, the major mango flavor compounds — β-myrcene and 3-methylbutyl butanoate — cannot be sensed => no mango flavor!

At the same time, the cool/cold activating aromas are exaggerated...and heptanal has a smell of dirty socks...

The following chart shows the relative odor activity values (OAVs) of these compounds in fresh and dried mango, according to the data from Bonneau et al.:


Odor activity values of selected compounds in fresh and dried mangoes. Data from Bonneau and her colleagues.*



As you can see, drying increases the OAVs of the two characteristic mango compounds, and completely eliminates mesifuran. The cool/cold-receptor-activating limonene increases slightly, while hexanal and heptanal make an appearance, so heptanal can offer its dirty odor.

Just thinking it would be very interesting to contrast mango-infused green tea with a mango-infused oolong. My guess is that the mango-ness would be enhanced and the dirty-sock effect diminished when you pair dried mango with a warm receptor activating oolong such as Tie Guan Yin. Give it a try?


* Bonneau, A., Boulanger, R., Lebrun, M., Maraval, I. and Gunata, Z. (2016), Aroma compounds in fresh and dried mango fruit (Mangifera indica L. cv. Kent): impact of drying on volatile composition. Int J Food Sci Technol, 51: 789–800. doi:10.1111/ijfs.13038

Saturday, April 15, 2017

Why do tea and books go so well together?

A fascinating article in The Guardian, based on research presented by Cecilia Bembibre and Matija Strlič,* may well have given the answer...

https://www.theguardian.com/books/2017/apr/07/the-smell-of-old-books-science-libraries

As you may know I have been hard at work clearing out my home of nearly thirty years (anniversary in August) in preparation for moving to be near my daughters and grandchildren. One of the difficult tasks has been to triage my many thousand volumes, each of which holds a special message for me -- books I read as a child, books that once belonged to my grandparents and even greatgrandparents, medical books, science books, math books, history books, school books, and especially books that my children loved to look at as toddlers and from which my parents and I read to them...

So I have been surrounded by that rich old book smell, and memories of curling up with a good book, cup of tea at hand, immersed another world.

Turns out that old book smell is made up of a number of compounds that are also contained in tea. The Historic Book Odor Wheel from the article (below) was created to show the different characteristic odors of an historic book and to indicate the corresponding compounds the authors were able to identify. I added red stars for compounds that are also present in tea, and a yellow arrow for limonene, which is present in bergamot and therefore in Earl Grey tea.



As you can appreciate, pleasant odors in the historic book are also present in tea, particularly in black tea (furfural and benzaldehyde). The "-al's" — hexanal, heptanal, and to a variable extent undecanal, are more characteristic of green teas, where they contribute to the grassy green flavors; and benzaldehyde is found in oolongs, too.

As I think about it, it's the lack of book smell that explains why I can't curl up with a good computer or Kindle.

* Cecilia Bembibre and Matija Strlič. Smell of heritage: a framework for the identification, analysis and archival of historic odours. Heritage Science20175:2
DOI: 10.1186/s40494-016-0114-1.
By the way, this article is open source so you can go on line to read it in its entirety, an exciting and worthwhile exercise because of the elegant discussion of smell as heritage:
https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-016-0114-1