The organism for February is the plant behind my favourite drink, tea. Camellia sinensis is a shrub native to East, South and Southeast Asia. It is now cultivated across the world in tropical and sub-tropical regions. In 2012 over 4.8 million tonnes of tea produced (1). The plants are harvested by hand every few weeks with only the bud and first 2-3 leaves removed.
Tea drinking originated in China where, according to legend, the Emperor Shen Nung discovered the drink in 2737 BC (this date seems rather precise to me!) Leaves from Camellia sinensis are processed in different ways to produce different types of tea. To make black tea, the leaves are allowed to oxidise during the drying process resulting in the darkening of the tea leaves as the chlorophyll breaks down and tannins are released. Green tea is made from tea leaves that have undergone minimal oxidation during drying. White tea, which is actually green in colour, is processed in a similar way to green tea, but only the youngest leads and buds are used to make it.
Like coffee, tea contains caffeine. There is some confusion regarding the caffeine content of tea compared with coffee. While at university I was told by a professor that tea contains just as much caffeine as coffee, but sedatives in tea counteract some of the stimulant effects of the caffeine.
Fresh tea leaves do have a higher caffeine content than coffee beans (2-3). However, since tea and coffee are made differently this doesn’t mean a higher amount of caffeine is present in a cup of tea. A study published in 2008 used a range of commercial varieties of tea to examine caffeine content (4). They found that 170 ml servings of tea contained between 14-61 mg of caffeine, which is typically lower than a cup of coffee (4). It is often said that most of the caffeine is released from tea leaves within the first 10-20 seconds of brewing. However, the scientists found that caffeine content of the tea increased much more slowly over the 5 minute brewing period.
The lack of a caffeine “ buzz” from tea drinking is due to the presence of an amino acid called L-theanine. It modulates the stimulant effects of caffeine by promoting relaxation but not drowsiness (5). The combination of L-theanine and caffeine seems to be able to improve performance in cognitive tasks.
Alongside a lower caffeine content, tea is also thought to be a healthier drink than coffee due to the presence of antioxidant compounds (catechins and polyphenols). Green tea contains higher amounts of the catechins whereas black tea contains more polyphenols (products of oxidation of catechins) (5). The most well-known class of polyphenols in tea are the tannins, responsible for the bitter taste and dark colour of tea.
(1) FAOSTAT. http://faostat.fao.org/DesktopDefault.aspx?PageID=567&lang=en#ancor . Retrieved 07/02/14
(2) Camellia sinensis (L.) Kuntze. http://www.hort.purdue.edu/newcrop/duke_energy/Camellia_sinensis.html. Retrieved 07/02/14
(3) Wikipedia: Coffee roasting. http://en.wikipedia.org/wiki/Coffee_roasting. Retrieved 07/02/14
(4) Chin et al (2008). Caffeine content of brewed teas. Journal of Analytical Toxicology.
(5) Compound interest Blog. Polyphenols and antioxidants – the chemistry of tea. http://www.compoundchem.com/2014/02/01/polyphenols-antioxidants-the-chemistry-of-tea/. Retrieved 07/02/14