Abstract
Extracts of 40 green, black or oolong high quality tea samples from China, Japan or India among others, have been prepared according to the manufacturer instructions and assayed for total polyphenols content using the Folin-Ciocalteu phenol reagent. In addition, the antioxidant activity was assessed by the CUPRAC method and the free-radical scavenging activity was determined using the antioxidant-promoting decay of the stable free-radical DPPH. Caffeine and the most important catechins were identified using RP-HPLC previously validated method. Results from this study suggest that teas, even though they content similar amounts of caffeine, differ considerably in polyphenolic content and therefore in antioxidant and free-radical scavenging activities, depending on the part of the plant used and the process applied to the material for the preparation of the final tea presentation. Correlations among Folin-Ciocalteau’s reactivity of tea samples, the neocuproine reactivity, the DPPH decolourization and the HPLC analysis suggest that the antioxidant activity is due essentially to polyphenolic compounds present in teas, mainly EGCG. The best extraction method of tea powder was the one indicated by dealers. In general, the richest samples belong to green teas and the poorest samples belong to the black teas.
Highlights
The benefits of tea polyphenols consumption have been well established
Among the standardized preparations enriched in green tea polyphenols is Polyphenon® which has been used in studies into inflammation-related colon carcinogenesis in mice [6] and in studies of catechin pharmacokinetics in healthy human beings [3] [5]
In order to gain insights on these differences we analysed forty tea samples from Asia, Europe and Africa countries obtained from different manufacturers for total phenolic content, antioxidant and anti-free-radical scavenging activities
Summary
The benefits of tea polyphenols consumption have been well established. Tea polyphenols are a source of valuable phytochemical compounds whose consumption may affect health and be beneficial for pathologies, like cardiovascular disorders and cancer [1] [2]. Among the standardized preparations enriched in green tea polyphenols is Polyphenon® which has been used in studies into inflammation-related colon carcinogenesis in mice [6] and in studies of catechin pharmacokinetics in healthy human beings [3] [5]. The combination of EGCG and sulindac significantly enhanced apoptosis in rat colon, reducing the aberrant crypt foci [8]. Despite these positive effects, administration of very large doses of concentrated green tea extracts has been shown to trigger certain adverse effects that rise concerns from a food safety point of view [9]-[11]. The aim of the present research was to compare the total phenolic content and the antioxidant and free-radical scavenging activities of a number of samples of different green, oolong and black teas from Asia and Africa prepared as water extracts as indicated by the dealers
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