1. Field of the Invention
The present invention relates to a novel method of making theanine.
2. Description of the Related Art
Theanine is known as a principal component of deliciousness of green tea and is an important substance as a flavor component of food such as tea. It is pointed out that γ-glutamyl derivative containing theanine acts as a biologically active substance in animals and plants. For example, it is reported that theanine or L-glutamine competes for convulsion caused by caffeine (Chem. Pharm. Bull. 19 (7) 1301-1307 (1971)). Thus, these compounds are considered to act on the central nervous system and expected to be useful as a biologically active substance.
Conventionally, theanine is generally extracted from dried tea leaves obtained in tea plantations where refined green tea containing theanine is produced. However, this method has two defects, namely, (1) only about 1.5% theanine is stored per predetermined amount of dried tea leaves and (2) photosynthesis is actively carried out in ordinary tea plantations and accordingly, synthesized theanine is quickly resolved, whereupon an amount of stored theanine is small. Thus, it is difficult and not practical to produce a sufficient amount of theanine by the extraction from the dried tea leaves.
Accordingly, new industrial production methods of theanine have been proposed. As one of the methods, a chemical organic synthesis of theanine has been reported (Chem. Pharm. Bull. 19 (7) 1301-1307 (1971)). However, the organic synthesis reaction has a low yield and requires a complicated operation in separation and refinement of composition and the like. Furthermore, an enzyme method has been reported as another industrial production method. In this enzyme method, theanine is synthesized from L-glutamine and ethylamine through the use of γ-glutamyl radical group transition reaction of glutaminase derived from Pseudomonas (JP-A-H11-225789). Additionally, another enzyme method has been developed in which this enzyme is fixed to a carrier (JP-A-H05-328986). However, when glutaminase derived from Pseudomonas is used, L-glutamic acid is synthesized as side reaction product by hydrolysis reaction as well as theanine. Accordingly, L-glutamic acid as a by-product complicates refinement of theanine.