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Background

Green tea has been an important part of food culture in Japan.Currently, there are various type of tea in the world, but in Japan, green tea is regarded as the most common type, and almost all tea produced in Japan is Green tea.

Green tea is recognized as medicine as well as beverage. Since ancient times, it has been known that green tea has health benefits to humans. With the increasing interest in the health benefits of green tea, the characteristics of components have been well studied.

L-Theanine

One of the beneficial components of green tea is L-theanine. Theanine, or γ-glutamylethlamide is a non-protein derived amino acid found solely in tea plant (Camellia sinensis). L-theanine is the most abundant amino acid in teas, and green tea contains more amount of amino acids than fermented ones [1]. It has been reported that theanine can reach to the brains and cause calming effect by promoting alpha brain waves [2]. It has also been reported in a rat test that theanine can act as a neurotransmitter and decrease blood pressure significantly in hypertensive rats[2] In addition to that, theanine gives distinctive flavor and savory taste to tea infusions, which is called as umami. For these reasons described above, green tea containing more theanine is considered to have the higher quality. One study shows that theanine content and green tea prices have strong positive correlation.[3]

In tea industry, monosodium glutamate(MSG) is often added to green tea to enhance its flavour,but that is the problem. The problem is that it's difficult to uncover such fake green tea. To distinguish the high-quality green tea (theanine) from the others(glutamate), we now need a sophisticated equipment.

Currently,theanine content in green tea is measured by instrumental analysis, but it costs and requires special technique for the measurement[4]. To solve this problem, we decided to create a biosensor which can measure the amount of theanine in green tea. Our goal this year was set to create a biosensor which is more sensitive to theanine than to glutamate.

Reference

[1] Wang, Lin, et al. "Analysis of free amino acids in Chinese teas and flower of tea plant by high performance liquid chromatography combined with solid-phase extraction." Food Chemistry 123.4 (2010): 1259-1266.
[2]Juneja, Lekh Raj, et al. "L-theanine—a unique amino acid of green tea and its relaxation effect in humans." Trends in Food Science & Technology 10.6 (1999): 199-204.
[3]] MUKAI, Toshihiro, Hideki HORIE, and Tetsuhisa GOTO. "Differences in free amino acids and total nitrogen contents among various prices of green tea." Chagyo Kenkyu Hokoku (Tea Research Journal) 1992.76 (1992): 45-50.
[4] Shimizu, Yoichiro, et al. "Sensitive enzymatic method for the quantification of theanine, a principal umami component of commercial tea beverages." Food Science and Technology Research 19.5 (2013): 909-913