Compositional Diversity and Functional Interactions of Bioactive Compounds in Japanese Green Tea: Focus on Matcha, Sencha, and Gyokuro.

Japanese green teas, including matcha, sencha, and gyokuro, are derived from the leaves of Camellia sinensis and contain bioactive compounds such as catechins, caffeine, and amino acids, notably theanine. However, the amounts and ratios of these components vary significantly depending on the harvest season, cultivar, and cultivation practices. Matcha products on the market range widely in quality, from high-grade ceremonial products to lower-quality powders. In sencha, compositional profiles differ not only according to harvest timing but also according to infusion conditions such as water temperature and steeping time. Gyokuro, a premium shaded tea, is a type of green tea with a particularly high theanine content, just like authentic matcha. The compositional differences are expected to influence the physiological and psychological functions of green tea. For instance, the stress-relieving effects of theanine are modulated not only by its concentration but also by its interactions with coexisting compounds such as caffeine and catechins. Similarly, the bioavailability and physiological activities of catechins may be altered by coexisting theanine and caffeine. This narrative review focuses on compositional variability and interactions among major bioactive compounds in Japanese green tea and discusses how these factors may influence their functional properties.