Quantification of theanine in tea beverages and evaluation of its antioxidant activity

Abstract

In today’s Japan, many individuals live in what is known as a stress society, where daily stress has become a common occurrence. The causes of stress vary from person to person and may be attributed to factors such as social environment and human relationships. Excessive stress can result in oxidative stress, which can have significant impact on both the mind and body. In fact, severe stress can lead not only to sleep disorders such as insomnia but also to mental illnesses such as depression. Theanine, a component derived from glutamic acid and ethylamine found in the roots of tea plants, is present in green tea and contributes to its umami taste. It has been approved as a functional food for stress and sleep. Theanine is known for its relaxing effects and its ability to improve sleep quality. Studies have also indicated its effectiveness in treating mental illnesses such as schizophrenia and depression. By understanding the functionality of theanine and investigating tea-based beverages that can be ingested most efficiently, it is believed that we can contribute to the prevention of diseases associated with reactive oxygen species generated by stress. In this study, we first evaluated the antioxidant effects of theanine using electron spin resonance (ESR) equipment. Next, we measured the amount of theanine in tea beverages using a liquid chromatograph/fluorescence detector (LC/FL). The ESR results demonstrated that theanine exhibits antioxidant activity by inhibiting the generation of reactive oxygen species through copper ions. Moreover, we found that Camellia sinensis, represented by green tea and black tea, contains a significant amount of theanine.