Physiological Activity and Component Changes with Magnesium Treatment before Tea Shade Cultivation

This study was conducted to determine the effect of magnesium treatment before shade cultivation during the 2nd and 3rd seasons to improve the productivity and quality of powdered green tea (matcha). On the 21st day of shading, the photosynthetic capacity was investigated using a portable chlorophyll fluorometer, and leaf chromaticity was analyzed using a colorimeter. After collecting the samples and freeze-drying them, phenolic compounds, antioxidant activity, catechin, caffeine, and free amino acids were analyzed. When grown under shade, the photosynthetic ability improved. Magnesium treatment further improved photosynthetic ability, which in turn increased the green color (G-value). Magnesium treatment decreased phenolic compounds, antioxidant activity, and secondary metabolites such as catechin and caffeine, but increased free amino acid content 2.7-fold compared to the non-shaded leaves and 1.4-fold compared to shaded leaves. Therefore, it is believed that magnesium treatment may contribute to improving the quality of matcha grown using shade cultivation.