Abstract
The contents of the chemical constituents of twenty-nine recently bred (hereafter refers to as "recent") and old varieties of Japanese green tea were compared at different harvest times and growth stages. The contents of total nitrogen (T-N), total-free amino acid (T-A), theanine (γ-glutamylmethylamine), tannin, caffeine and vitamin C were analyzed by the near infrared spectroscopic method. At the first flushes, the contents of T-N, T-A and theanine, which affect the quality of tea, were high in the recent varieties of tea. However, the content of caffeine, which is a major nitrogen compound and which contributes to the characteristic bitter taste of tea, did not differ between the recent and old varieties of tea. The amount of tannin, which contributes to the astringent taste of tea, was lower in the recent varieties. In the mature leaves, the contents of T-N, T-A and theanine were high in the recent varieties of tea. However, no significant correlation was observed in tannin content between recent and old varieties of tea. In addition, there were positive correlations in the amounts of T-A between the first flushes and mature leaves both in the recent and old varieties of tea. Subsequently, the shoots with three leaves and one bud of ten of the 29 varieties were harvested at the first flushes at the fifth stage on May 4, 14 and 17 and analyzed by standard chemical methods. Higher contents of T-N and soluble nitrogen (corresponding to T-A) were observed in these recent varieties. The results showed that the recent varieties of tea contained higher nitrogen and lower tannin levels, suggesting that the recent varieties had been selected according to the changes in the breeding objectives from high yield to quality due to the changes in the consumers' demand. Modern cultivation methods, such as the use of frost-protecting fan, pest control and rate of fertilizer application, etc., have contributed to raising tender clones with higher quality in the experimental fields of many tea breeders in Japan. Furthermore, it was suggested that it might be possible to estimate the contents of the chemical constituents of tea flushes by analysing the overwintering leaves before the first cropping season or three leaves and one bud harvested at anytime in the first cropping season.
