Variation of Antioxidant in Tea Leaves Grown in Chiang Mai and Chiang Rai

Abstract

The purpose of this experiment is to study the variation of  the antioxidant, Epigallocatechin gallate ( EGCG) levels in tea leaves of different tea varieties, environment and cultivation practices in four selected sites of Chiang Mai and Chiang Rai provinces. The different responses among tea varieties were slightly found under the same season but clearly found under the different seasons. A peak of EGCG substance appeared in hot season and the substances decreased in rainy season but increased again in cool season. Negative correlations were found between EGCG and the moisture of tea leaves, relative humidity of the air and elevations. Therefore, the EGCG substance will drop down when the moisture of tea leaves increased during rainy season and when the elevations increased. In addition, the elevations showed the negative correlation with pH (P≤0.01) and the pH showed the positive correlation with phosphorus and potassium levels in soil. In conclusion, high level of EGCG substance can be found in hot season and it promote the taste and quality of the tea leaves. To pluck high level of EGCG quantity and good quality of tea leaves, tea leaves must be processed during hot season, followed with cool and rainy season. Finally, EGCG substance negatively varied with elevation levels.