Abstract
Objectives: The objective of the study was to estimate the seasonal variations in the antioxidant capacities, total polyphenol content (TPC), total flavonoid content (TFC), and tannin content (TC) of tea leaf extracts from two different plantation sites.
 Methods: Samples were collected from two tea gardens in Tuli and Ungma situated at N 26°39’19.3 E 094°39’22.7 and N 26°17’30.6 E 094°28’29.2, respectively, under the Mokokchung district of Nagaland, India. TPC, TFC, and TC from sample extracts were determined using Folin–Ciocalteu reagent, aluminum chloride colorimetric, and Folin–Ciocalteu assay. Apart from these, antioxidant capacities were analyzed using ferric reducing ability of plasma (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay.
 Results: The concentrations of total polyphenol, flavonoid, and tannin varied from 552.029±8.079 to 305.647±1.744 mg gallic acid equivalent/g, 238.770±0.508–148.457±1.653 mg catechin equivalent/g, and 26.453±0.485–20.173±0.173 mg tannic acid equivalent/g, respectively. FRAP and DPPH assay displayed value ranging from 2.564±0.023 to 1.074±0.023 mmol Fe(II) equivalent/g and 3.612±0.053–2.076±0.028 mmol Trolox equivalent/g. Significant seasonal variations in concentrations of these compounds were observed and a positive correlation between antioxidant capacities and phenolics of tea leaf extracts was established.
 Conclusion: Tea (Camellia sinensis (L.) O. Kuntze) has been regarded as a plant of immense medicinal and therapeutic value since time immemorial. The tea leaf extracts analyzed in this study gave high TPC, TFC, and TC, as well as high antioxidant activity in terms of DPPH and FRAP value. Studying such properties in tea leaves contributes more to our understandings of health benefit potentials in tea leaves and the quality of tea leaves on the basis of seasons and sites where they are planted.
Highlights
total polyphenol content (TPC), total flavonoid content (TFC), and tannin content (TC) The TPCs of the tea leaves were in the order Tspr>Tsum>Taut>Uspr>Usum>Uaut>Twin>Uwin with the highest and the lowest TPC up to 552.029±8.079 mg gallic acid equivalent (GAE)/g and 305.647±1.744 mg GAE/g, respectively (Table 1)
Tannin concentration in tea leaf extracts was in the order Uspr>Tsum>Tspr>Usum>Uaut>Taut>Twin>Uwin with the highest and the lowest TC up to 26.453±0.485 mg tannic acid equivalent (TAE)/g and 20.173±0.173 mg TAE/g, respectively (Table 1)
Antioxidant capacities by DPPH and ferric reducing ability of plasma (FRAP) assay The highest antioxidant capacity with 3.612±0.053 mmol Trolox equivalent (TE)/g was seen in Tspr while the lowest value with 2.076±0.028 mmol TE/g was seen in Uwin (Table 2)
Summary
Studies reported wide health benefits of tea consumption including a reduction in cardiovascular mortality [8] and protective effect against many different types of cancer [9]. In vitro studies reported the preventive effect of tea against cellular DNA damage caused by arsenic-mediated oxidative stress [10]. These benefits of tea have been attributed mainly to its phytochemicals such as polyphenols which are important constituents of the human diet widely distributed in vegetable foods an [11]. Flavan-3-ols, commonly known as catechins, are the major polyphenolic compounds in tea and it includes (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCG), (−)-gallocatechin (GC), and (−)-gallocatechin gallate (GCG) [15]. Apart from many health benefiting properties, tea catechins are responsible for the bitter taste and dark color of black tea due to oxidation and condensation to theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3-3′-digallate and thearubigins during fermentation [16]
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