Quantitative analysis of major constituents in green tea with different plucking periods and their antioxidant activity

Abstract

The objective of this study was to determine the relationship between the plucking periods and the major constituents and the antioxidant activity in green tea. Green tea was prepared from leaves plucked from the end of April 2013 to the end of May 2013 at intervals of one week or longer. The contents of theanine, theobromine, caffeine, catechin (C), and gallocatechin gallate (GCg) were significantly decreased, whereas those of epicatechin (EC), epigallocatechin gallate (EGCg) and epigallocatechin (EGC) were significantly increased along with the period of tea leaf plucking. In addition, antioxidant activity of green tea and standard catechins was investigated using ABTS, FRAP and DPPH assays. The highest antioxidant activity was observed in relatively the oldest leaf, regardless of the assay methods used. Additionally, the order of antioxidant activity of standard catechins was as follows: EGCg≥GCg≥ECg>EGC≥GC≥EC≥C. Moreover, the cis-catechins contents were the key factor affecting the antioxidant activity of green tea in all assays employed (ABTS, r=0.731, p<0.01; FRAP, r=0.886, p<0.01; DPPH, r=0.778, p<0.01).

Figure 1

HPLC chromatograms of standard solution and green tea extracts with different plucking periods. Peaks correspond to (1) theanine, (2) theobromine, (3) gallic acid, (4) (+)-gallocatechin, (5) caffeine, (6) (−)-epigallocatechin, (7) (+)-catechin, (8) (−)-epicatechin, (9) (−)-epigallocatechin gallate, (10) (+)-gallocatechin gallate, (11), (−)-epicatechin gallate and (12) (+)-catechin gallate. Woojeon, first flush leaf of late April; Sejak, second flush leaf of early May; Joongjak, third flush leaf of mid-May; Daejak, fourth flush leaf of late May.

Figure 2

Antioxidant activity expressed as Trolox equivalent (mM TE) in standard catechins measured by ABTS, FRAP and DPPH assays. All values are mean ± SD. Values with different letters are significantly different by ANOVA with Tukey’s post hoc test at p < 0.05. GC, (+)-gallocatechin; EGC, (−)-epigallocatechin; C, (+)-catechin; EC, (−)-epicatechin; EGCg, (−)-epigallocatechin gallate; GCg, (+)-gallocatechin gallate; ECg, (−)-epicatechin gallate.