Effects of enzyme treatment on volatile and non-volatile compounds in dried green tea leaves

Green tea contains polyphenols, mainly four catechins, including (-)-epigallocatechin gallate, (-)-epicatechin gallate, (-)-epigallocatechin, and (-)-epicatechin. Enzyme tannase is known to hydrolyze gallated catechins into non-gallated catechins and gallic acid (GA). In this study, dried green tea leaves were treated with tannase to determine changes of volatile and non-volatile compounds by the hydrolysis. The results indicated that (-)-epigallocatechin, (-)-epicatechin, and GA increased, while (-)-epigallocatechin gallate and (-)-epicatechin gallate decreased after the treatment. The GA level increased in the treated samples, which increased titratable acidity significantly, while the pH became lower. Furthermore, the antioxidant activity of the tannase-treated tea leaves increased. The level of glycosidically bound aromas decreased with the concomitant increase of corresponding volatile compounds, while some alcohols derived from fatty acids decreased significantly after the treatment. These results suggest that tannase-treatment influences both volatile and non-volatile compounds in dried green tea leaves.