What is the most popular drink after water? We dare to say that the answer is tea. It is known that ancient civilizations used to drink it. However, the first literature descriptions of tea use are dated about 300 years of the new era. Within this paper, we focus on the science behind this fantastic drink.

Image Credit: Martyna Kaźmierczak & Science Embassy

Color and aroma

There are many tea types, but the main are white, green, red, black, yellow tea. There are also other tea types like hibiscus-based one or herbal tea, while that is a different story. Let’s focus only on these types that come from the tea tree without flavor additives. Tea leaves are harvested, dried, and here the story begins. Each one has a different history of its preparation.

Black tea is made from leaves that are exposed to sunlight for a long time after harvesting. This way, the leaves are oxidized and turn black. Yellow tea also called oolong tea is also dried on air, while its exposure to sunlight is much shorter, so leaves stay lighter. They are only partially oxidized. Green ones are not oxidized at all. They are steamed or pan-cooked to prevent leaves from oxidation. Then, they are dried. This way, naturally, green leaves stay green. White tea is made from baby-leaves that are steamed and dried directly after harvesting. What about the red one? In fact, it is a mixture of black tea with flavors or different leaves [1].

Essential molecules

Tea contains many chemical compounds that have a tremendous influence on our bodies. For that reason originally it was used for medicinal purposes, e.g. detoxification. One of these molecules is caffeine. The same one is present in coffee, while often in tea is called teine or theine instead of caffeine. It is an alkaloid that influences the central nervous system. That molecule enhances cognition, alertness and improves athletic performance [2]. It reduces physical fatigue, while overdoses may cause an increase in blood pressure and anxiety [3].

On the one hand, the tea contains caffeine that increases our attention, while on the other hand, it has a relaxing effect on us. The relaxing and antistress effect of tea comes mainly from L-theanine. Still, some research says that it may be both L-theanine’s synergistic work and mentioned above catechins. L-theanine also makes your sleep much better and may help with depression. In combination with caffeine also helps to focus attention during cognitive tasks [4]. That unique molecule can be found in all tea types [5]. Why does L-theanine affect us in this way? It increases alpha waves in the brain, which are generally considered an index of relaxation [6]. Our brain produces them when we are awake but stay relaxed. Some studies show that this chemical compound even helps to manage stress and anxiety [7].

Tea contains, besides caffeine, another stimulant compound – theobromine. Theobromine is a kind of alkaloid found not only in tea but also in cocoa and cola nuts [8]. However, it has a considerably weaker stimulating effect than caffeine. Did you know that theobromine has a beneficial impact on our health (mood and brain functions)? First, it gives a short-term boost to the brain, probably by improving the brain’s blood flow.

Moreover, it improves motivation, focus, alertness, and cognition [9]. Working oppositely to caffeine can lower blood pressure. It also improves breathing by acting as a lung relaxant [10].

Another chemical compounds present in tea are polyphenols [11]. Their amount in tea depends on plantation elevation and leaf size. Black tea from low plantation elevation contains over 25% more polyphenols than those from a high elevation. Small tea leaves have up to more polyphenols than larger ones. These chemicals are natural antioxidants and can also be found in coffee, berries, grapes, and wine. There are many types of polyphenols. One of them that are present in tea called flavonoids having a beneficial influence on health. They are considered valuable ingredients in nutraceutical, pharmaceutical, cosmetical, and even medicinal applications. Among many flavonoids, the most significant are catechins. Green tea has more catechins than black tea. [12]. These compounds are known to have antibacterial, antiviral, and hepatoprotective properties [13]. It won’t be surprising if we dare say that these features cause that tea often-drinkers are less often ill or have fewer [1]. In general, their use prevents infectious diseases [14].

Did you know that?

  • The world’s most expensive tea is called Da Hong Pao. The process of making this tea is still a secret. It is considered a national treasure, and the Chinese give this tea to essential individuals or celebrities [15].
  • Tea may be decaffeinated using a procedure in which the caffeine is removed from leaves by carbon dioxide with no influence on all aroma and features of tea. Unfortunately, it is an expensive procedure, so tea costs are also higher than regular ones. An intriguing way to decaffeinate uses microorganisms that use caffeine as a source of nitrogen and carbon. These microorganisms have immense potential, but that method still is not used for industrial decaffeination [16].
  • Most catechins have jasmine tea, and it also has higher antioxidant and anticancer activity. The same shows blueberry and pomegranate teas, but their features may be indicated by other antioxidants [17].
  • Plastic teabags release tiny particles or fibers called microplastic. When consumed, microplastic can release harmful chemicals. So, it is better to drink tea that is not packed in teabags [18].

Summary

Everybody is looking for a different taste during the first sip of tea. Because everybody prefers distinct tastes and customers love the diversity in choice, producers add some flavor to other plants. Some of us prefer to drink tea as the primary beverage, while others drink it only from time to time. There are many tea types like white, green, and much, and probably each of us has a favorite one. Tea is a natural source of caffeine and antioxidants. Sometimes it is drunk on the go, and sometimes traditionally. It has beneficial effects on health. However, it should be consumed moderately due to the caffeine content, excluding decaffeinated one.

This article is a joint work of Martyna Kaźmierczak (Faculty of Chemistry, University of Warsaw), Magdalena Warczak (Institute of Physical Chemistry, Polish Academy of Sciences), and Magdalena Osial (Faculty of Chemistry, University of Warsaw) as a part of the Science Embassy project.

References

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[2] J.M. Chin, M.L. Merves, B.A. Goldberger, A. Sampson-Cone, E.J. Cone. “Caffeine content of brewed teas”, J Anal Toxicol., 2008, 32(8):702–704. DOI: 10.1093/jat/32.8.702.

[3] J.G. Lisko, G.E. Lee, J.B. Kimbrell, M.E. Rybak, L. Valentin-Blasini, C.H. Watson. “Caffeine concentrations in coffee, tea, chocolate, and energy drink flavored e-liquids”, Nicotine Tob Res., 2017, 19(4):484–492. DOI: 10.1093/ntr/ntw192.

[4] National Center for Biotechnology Information. PubChem Compound Summary for CID 439378, L-Theanine. https://pubchem.ncbi.nlm.nih.gov/compound/L-Theanine. Accessed Feb. 07, 2021.

[5] K. Boros, N. Jedlinszki, D. Csupor. “Theanine and caffeine content of infusions prepared from commercial tea samples”, Pharmacogn Mag., 2016, 12(45):75-79. DOI: 10.4103/0973-1296.176061.

[6] L. Juneja. “L-theanine — a unique amino acid of green tea and its relaxation effect in humans”, Trends Food Sci. Technol., 1999, 10(6-7):199-204.  DOI: 10.1016/S0924-2244(99)00044-8.

[7] J.L. Williams, J.M. Everett, N.M. D’Cunha NM, D. Sergi, E.K. Georgousopoulou, R.J. Keegan, A.J. McKune, D.D. Mellor, N. Anstice, N. Naumovski. “The effects of green tea amino acid L-theanine consumption on the ability to manage stress and anxiety levels: a systematic review”, Plant Foods Hum Nutr., 2020, 75(1):12-23. DOI: 10.1007/s11130-019-00771-5.

[8] https://www.technology.org/2021/02/08/cocoa-chocolate-and-chemistry/ (accessed 18.02.2021).

[9] H.J. Smit. “Theobromine and the pharmacology of cocoa” In: “Methylxanthines”, Springer Berlin Heidelberg; 2010:201-234. DOI: 10.1007/978-3-642-13443-2_7.

[10] E. Sato, E. Tamagawa, K. Naito, M. Nirasawa, I. Ashida, S.Miyaoka, Y. Miyaoka. Influence of sex differences on temporal sequence of sensations after ingesting fruit-flavored tea — A preliminary study”, Food Nutr Sci., 2018, 9(6):676-682. DOI: 10.4236/fns.2018.96051.

[11] J. Yang, R.H. Liu. “The phenolic profiles and antioxidant activity in different types of tea”,  Int J Food Sci. Technol., 2013, 48(1):163-171. DOI:10.1111/j.1365-2621.2012.03173.x.

[12] C. Zhang, CL-C. Suen, C. Yang, S.Y. Quek. “Antioxidant capacity and major polyphenol composition of teas as affected by geographical location, plantation elevation and leaf grade”, Food Chem., 2018, 244:109-119. DOI: 10.1016/j.foodchem.2017.09.126.

[13] C. Musial, A. Kuban-Jankowska, M. Gorska-Ponikowska. “Beneficial properties of green tea catechins”, Int J Mol Sci., 2020, 21(5):1744. DOI: 10.3390/ijms21051744.

[14] W.C. Reygaert. “Green tea catechins: Their use in treating and preventing infectious diseases”, Biomed Res Int., 2018, 2018:9105261. DOI: 10.1155/2018/9105261.

[15] https://www.teabloom.com/blog/5-most-expensive-teas-in-the-world/ (accessed 18.02.2021).

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[17] B. Alappat, J.A. Sarna, C. Truong. “Anticancer and antioxidant properties of flavored green tea extracts”, J Agric Life Sci., 2015, 2:15–24.

[18] L.M. Hernandez, E. Genbo Xu, H.C.E. Larsson, R. Tahara, V.B. Maisuria, N. Tufenkji. “Plastic Teabags Release Billions of Microparticles and Nanoparticles into Tea”, Environ. Sci. Technol., 2019, 53(21):12300–12310. DOI: 10.1021/acs.est.9b02540.




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