The effects of circadian rhythm on catechin accumulation in tea leaves

As the major bitter- and astringent-tasting components in tea leaves, catechins play an essential role in determining flavor characteristics and health benefits of tea products. This study analyzed the circadian rhythm effects on the accumulation pattern of catechins in tender leaves of three tea cultivars, 'Huangkui' (HK), 'Longjing43' (LJ43) and 'Fuding Dabaicha' (FD). There were two major factors involved in the catechin regulation in tea plants: genetic background of the cultivar-specific regulation, and temporal effects of the circadian rhythm. Etiolated leaves of 'HK' contained lower levels of catechins than 'LJ43' and 'FD'. The composition of EGCG in total catechins was significantly higher in 'LJ43' leaves (65%) when compared with that in 'HK' and 'FD' (45%). The accumulation of individual catechins increased during the daytime but decreased overnight, especially over the time period of 22:00−02:00. The correlation analysis between catechins and environmental factors indicated catechin accumulation in tea leaves potentially resulted from a combined regulation of light and temperature. These findings provide new insights into our understanding of circadian rhythm regulation on flavor-important secondary metabolites in tea leaves.