Wine experts have a popular phrase — vine must suffer, meaning that in order to get good wine, the grape plant itself must grow in uncomfortable conditions. A similar principle applies to tea — many of its virtues, as it turns out, are a direct consequence of the suffering experienced by tea leaves. It is called not suffering, but stress, but this does not change the essence.
Tea, as well as other popular products, often becomes the subject of scientific research. To see this, it is enough to install a filter for tea and caffeine (as a bonus) on any scientific data aggregator — and after a week, you will start puzzling over what can be done with this array of potentially interesting, but extremely heterogeneous and not always easy-to-understand information.
Moreover, at first glance, this information may seem not to have any practical value. Most scientific research is related to the cultivation and production of tea or its effect on health. And the majority of tea specialists in consumer tea culture are engaged in preparation and service of the drink, rather than its production or use for medical purposes.
However, the answer to the question of how to use scientific news can be found in the professional profile of the consumer culture specialist. The fact is that an important part of their work with clients is entertaining stories. A good tea master should be a good storyteller. Do not forget that one of the options for the professional development of a tea master is their gradual transformation into an expert, when their ability to tell stories turns into the ability to write expert texts.
Scientific news is an excellent building material for both entertaining stories and expert articles. Even if they are dedicated to very specific issues.
Amino Acids in Tea
Zhenming Yu and Ziyin Yang described the formation mechanisms of different amino acids in tea during its production. Amino acids in tea partially determine its taste, aroma and physio-logical effect. At the same time, tea leaves contain both proteinaceous and non-proteinaceous amino acids (proteinaceous amino acids can be part of proteins, but non-proteinaceous amino acids can’t). The taste and aroma are influenced mainly by proteinaceous amino acids. And non-proteinaceous tea amino acids include such popular substances as L-theanine and GABA (gamma-aminobutyric acid).
It turns out that proteinaceous amino acids are mainly the product of protein degradation, which occurs at all stages of the existence of a tea leaf, including both its growth and technological processing. And, accordingly, the content of proteinaceous amino acids in tea is largely determined by external factors — both natural and technological.
As for non-proteinaceous amino acids, everything is somewhat more complicated about them. The accumulation of L-theanine depends more on the tea cultivar than on external conditions. While GABA accumulation is a result of mechanical damage to the leaves and the anoxic stress which they receive in the oxygen-free environment.
You’ll probably admit that this is very pompous to offer your guests GABA-tea as a result of a unique combination of mechanical and anoxic stress.
Stress and Aroma of Albino Tea
Chinese scientists have compared the effect of stress on ordinary green tea leaves and albino tea leaves.
The fact that continuous wounding stress (caused by twisting, insect infestation, etc.) stimulates the formation of aromatic substances in tea leaves is well known. It is this property of tea leaves that often explains the specific and vivid aroma of oolongs, especially those made from already damaged leaves (Oriental Beauty and its replicas). The ‘aroma in response to stress’ mechanism has not been understood one hundred percent, but it is definitively known that tea leaves that were exposed to stress contain more aromatic substances such as jasmine lactone, nerolidol and some others. Analysis of changes in the content of these substances allows us to evaluate the reaction of different leaves to stress, which, in fact, the scientists did by comparing green leaves with albino ones.
Albino teas are the varieties of tea plants the leaves of which, under certain conditions (associated with light and temperature), become noticeably lighter than those of normal tea plants. In addition to the obvious problem with chloroplasts (which, among other things, provide plants with a green color), albino teas have other specific characteristics — for example, they have less caffeine and catechins and more amino acids than normal tea. Besides, teas made from albino leaves (mostly green teas), as a rule, have a slightly weaker aroma and slightly sweeter taste.
And this aroma, in fact, became the main theme of the present study. The leaves of the same tea cultivar in its normal and mutated (albino) form were subjected to stress, and it appeared that the ‘aroma in response to stress’ reaction in albinos is present, but not so strong. So, the scientists drew three conclusions.
First, in response to continuous wounding stress, a chloroplast defect of albino teas significantly reduces the production of some aromatic components (volatile fatty acid derivatives: jasmine lactone and other compounds) and does not affect the production of the others (for example, indole and nerolidol).
Second, the ‘aroma in response to stress’ mechanism starts in both normal and albino tea leaves. But why the content of some aromatic substances increases in albinos after stress while the content of the others does not is not yet clear. Perhaps it’s all about hydroperoxide lyase, which is involved in the last stages of the synthesis of volatile fatty acid derivatives, such as the above mentioned jasmine lactone (which, by the way, has a pleasant ‘fruit-and-floral aroma’) and other compounds responsible for the ‘green leaf aroma’. It only remains to check whether the chloroplast defects in albino leaves affect the activity of hydroperoxide lyase.
Third, continuous wounding stress can be used to enhance the aroma of albino tea. Traditionally, albino tea plants are used for the production of green teas, which, as compared with oolongs, are treated rather delicately. And if you stop playing nice with albino tea leaves, perhaps they will be more fragrant.
Although, to be honest, they are tasty enough already.
Drought Stress and Aroma of Tea
Chinese scientists have studied the effect of drought on the chemical composition of tea leaves.
They have discovered that slight drought stress stimulates formation of polyphenols in tea leaves, while serious drought stress, on the contrary, inhibits their formation. In addition, the lack of watering enriched some volatile metabolite pathways; this indicates that drought stress might affect the tea aroma.
(E)-Nerolidol Is Formed in Oolongs under Stress
(E)-Nerolidol is a volatile sesquiterpene that contributes to the floral aroma of teas. Since (E)-nerolidol is not known to form in tea leaves, the mechanism of its formation in tea was an interesting issue for the Chinese scientists.
During their experiments, the specialists discovered that in tea leaves undergoing continuous mechanical damage, farnesyl diphosphate (found in tea cells) transforms into (E)-nerolidol under the action of special enzyme, activated by this mechanical damage. If, in addition to mechanical damage, tea leaves are also subjected to low-temperature stress, there will be even more nerolidol in them (toss and bruise your oolongs in the refrigerator, colleagues).
Such a mechanism of the formation of volatiles is not unique to tea. In response to damage, a number of plants produce odorous substances, which sometimes have rather funny names, e.g. bergamotene. The words sesquiterpene and bergamotene need to be remembered and used when serving fragrant tea to guests.
Jasmine Lactone and the Sufferings of Tea
Jasmine lactone is one of the aromatic components of tea, responsible for the sweet, fruity and floral notes in its fragrance. Most of jasmine lactone is accumulated in oolong tea — therefore this type of tea was studied by Chinese researchers in order to determine the mechanism of synthesis behind the such a pleasant aromatic component.
It turned out that the synthesis of jasmine lactone is a consequence of the stresses to which tea leaves are exposed during the growth and manufacturing processes. And the sources of these stresses can be both mechanical damages of tea leaves and thermal effects.
In short, while breathing in the pleasant aroma of tea, one must always remember that this fragrance is the result of constant and varied suffering.
