Abstract
Black tea was extracted for 2, 8 and 18 h with absolute acetone, N,N-dimethyl-formamide (DMF), ethanol and methanol and their 50% aqueous solutions. The extracts were screened for total polyphenol contents, antioxidant and antibacterial activities. The polyphenol content of the extracts was found to be in the range of 0.44-114.01 mg gallic acid equivalents (GAE)/g dry weight tea, depending on the solvent used and the length of the extraction process. In general, aqueous acetone or DMF extracts displayed the highest polyphenol contents and antioxidant activity, while absolute acetone was the least efficient solvent. Antioxidant activities of tea extracts tested using the reducing power and 2,2-diphenyl-1-picryhydrazyl (DPPH) radical methods ranged from 0.09 to 1.18 and from 2.60 to 95.42 %, respectively, depending on the extraction conditions and the antioxidant activities correlated well with the polyphenol concentrations. Aqueous solvent black tea extracts also possessed antibacterial activity, depending on the solvent used and bacterial species tested. Staphylococcus aureus was found to be the most sensitive to all tea extracts, except for the methanol extract. Tea extracts were not effective against Y. enterocolitica, L. monocytogenes and E. coli O157:H7.
Highlights
IntroductionThe growing interest in the potential health benefits of tea, together with its popularity as a beverage, have prompted numerous investigations on the chemical constituents of tea and their biological properties [1], such as antimutagenic [2], anticarcinogenic and antioxidant [3,4], antibacterial [5,6] and antiallergic activities [7]
Tea is a widely consumed beverage throughout the world
The results showed that the variation in polyphenol content with increasing extraction time varied depending on solvent used, which was reported previously for Orthosiphon stamineus plants [16]
Summary
The growing interest in the potential health benefits of tea, together with its popularity as a beverage, have prompted numerous investigations on the chemical constituents of tea and their biological properties [1], such as antimutagenic [2], anticarcinogenic and antioxidant [3,4], antibacterial [5,6] and antiallergic activities [7]. We compared various solvent systems including water and neat DMF, acetone, and methanol or ethanol and various concentrations of these organic solvents in water (50 and 80 %) for the polyphenol content in the resulting extracts and the antioxidant activity of teas. One was the DPPH radical scavenging assay most widely used for studying polyphenols from plants, including tea, and the other is reducing power (RP) which was chosen due to the fact that iron-polyphenol complex was demonstrated to cause the inhibition of formation of oxygen radicals associated with many pathological conditions [10] and probably growth of some pathogen microorganisms [5]
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