Phytochemicals occluded in tea have been extensively used as dietary supplements and as natural pharmaceuticals in the treatment of various diseases including human cancer. Results on the reduction capabilities of phytochemicals present in tea to reduce gold salts to the corresponding gold nanoparticles are presented in this paper. The phytochemicals present in tea serve a dual role as effective reducing agents to reduce gold and also as stabilizers to provide a robust coating on the gold nanoparticles in a single step. The tea-generated gold nanoparticles (T-AuNPs), have demonstrated remarkable in vitro stability in various buffers including saline, histidine, HSA, and cysteine solutions. T-AuNPs with phytochemical coatings have shown significant affinity toward prostate (PC-3) and breast (MCF-7) cancer cells. Results on the cellular internalization of T-AuNPs through endocytosis into the PC-3 and MCF-7 cells are presented. The generation of T-AuNPs follows all principles of green chemistry and T-AuNPs have been found to be non toxic as assessed through MTT assays. No ‘man made’ chemicals, other than gold salts, are used in this truly biogenic, green nanotechnological process thus paving the way for excellent opportunities for their application in molecular imaging and therapy.

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Green nanotechnology from tea: phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles

Phytochemicals occluded in tea have been extensively used as dietary supplements and as natural pharmaceuticals in the treatment of various diseases including human cancer. Results on the reduction capabilities of phytochemicals present in tea to reduce gold salts to the corresponding gold nanoparticles are presented in this paper. The phytochemicals present in tea serve the dual roles as effective reducing agents to reduce gold and also as stabilizers to provide robust coating on the gold nanoparticles in a single step. The Tea-generated gold nanoparticles (T-AuNPs), have demonstrated remarkable in vitro stability in various buffers including saline, histidine, HSA, and cysteine solutions. T-AuNPs with phytochemical coatings have shown significant affinity toward prostate (PC-3) and breast (MCF-7) cancer cells. Results on the cellular internalization of T-AuNPs through endocytosis into the PC-3 and MCF-7 cells are presented. The generation of T-AuNPs follows all principles of green chemistry and have been found to be non toxic as assessed through MTT assays. No 'man made' chemicals, other than gold salts, are used in this true biogenic green nanotechnological process thus paving excellent opportunities for their applications in molecular imaging and therapy.

Phytochemicals in tea as building blocks for production of biocompatible gold nanoparticles

Extraction and quantification of polyphenols from kinnow (Citrus reticulate L.) peel using ultrasound and maceration techniques

Background: The role of non-polymeric phenolic (NP) and polymeric tannin (PT) constituents in the antioxidant and antibacterial properties of six brands of green, black, and herbal teas of Camellia sinensis were investigated. Materials and Methods: Total phenolic content (TPC) and ascorbic acid equivalent antioxidant capacity (AEAC) were assessed using the Folin-Ciocalteu and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays, respectively. Minimum inhibitory dose (MID) against Gram-positive Micrococcus luteus, Staphylococcus aureus, and Bacillus cereus, and Gram-negative. Escherichia coli, Salmonella typhi, and Pseudomonas aeruginosa was assessed using the disc-diffusion method. Teas were extracted with hot water successively three times for one hour each time. The extracts were fractionated using Sephadex LH-20 column chromatography to obtain the NP and PT constituents. Results: Extraction yields ranged from 12 to 23%. Yields of NP fractions (70−81%) were much higher than those of PT fractions (1−11%), suggesting that the former are the major tea components. Ranking of antioxidant properties of extracts was green tea>black tea>herbal tea. For all six teas, antioxidant properties of PT fractions were significantly higher than extracts and NP fractions. Extracts and fractions of all six teas showed no activity against the three Gram-negative bacteria. Green teas inhibited all three Gram-positive bacteria with S. aureus being the least susceptible. Black and herbal teas inhibited the growth of M. luteus and B. cereus, but not S. aureus. The most potent were the PT fractions of Boh Cameron Highlands and Ho Yan Hor with MID of 0.01 and 0.03 mg/disc against M. luteus. Conclusion: Results suggested that NP constituents are major contributors to the antioxidant and antibacterial properties of teas of C. sinensis. Although PT constituents have stronger antioxidant and antibacterial properties, they constitute only a minor component of the teas.

Antioxidant and antibacterial properties of green, black, and herbal teas of Camellia sinensis.

Catechins: Sources, extraction and encapsulation: A review

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.

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Effect of Extraction Conditions on Measured Total Polyphenol Contents and Antioxidant and Antibacterial Activities of Black Tea

Polyphenol content, polyphenol yield, antioxidant and antibacterial activities of methanol, ethanol and water extracts and their crude, ethyl acetate and water fractions derived from fresh tea leaves (FTL) and green tea (GT) were evaluated. Ethyl acetate fractions of ethanolic extracts contained the highest polyphenol content in FTL and GT samples (680.2 and 560.8 mg gallic acid equivalent g -1 dry extract, respectively). For each of 3 extraction solvents, ethyl acetate fractions always had highest polyphenol content, for both teas. Ethyl acetate fractions of water extracts of FTL and GT had highest antioxidant activity (80.8 and 78.6 g ascorbic acid 100g -1 dry extract). A rather high correlation coefficient (R 2 = 0.9376 for FTL and 0.9783 for GT) was obtained between antioxidant activity to total polyphenol content for both tea. Ethyl acetate fractions of extracts showed antibacterial activity on S. aureus and B. cereus . Crude extract of FTL were also effective on S. aureus .

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Antioxidant and antibacterial activities of various extracts and fractions of fresh tea leaves and green tea.

Black mate tea was extracted with different 50% solvents (acetone, N,N-dimethyl formamide (DMF), ethanol and methanol) for 2, 8 and 18h. The extracts were screened for polyphenol content, antioxidant and antibacterial activities. Total polyphenol content of the extracts ranged from 97.01 to 119.28mg gallic acid equivalent (GAE)/g dry weight (dw) tea depending on the solvent used and extraction time applied. In general, methanol was the least efficient solvent for polyphenol extraction from black mate tea and the efficiency of the others was found to be similar. All extracts showed antioxidant activity by 2,2-diphenyl-1-picryhydrazyl (DPPH) radical and reducing power. Different trend was observed for each method with respect to solvents used. The extracts possessed antibacterial activity depending on the solvent used and bacterium tested and the results sowed that black mate tea extracts had strong antimicrobial activity against selected bacteria, except for E. coli O157: H7. While S. aureus was found to be the most sensitive to all extracts, E. coli was the most resistant among bacteria tested.

Gökçe Polat

Papers

Effect of Extraction Conditions on Measured Total Polyphenol Contents and Antioxidant and Antibacterial Activities of Black Tea

Antioxidant and antibacterial activities of various extracts and fractions of fresh tea leaves and green tea.

Total Polyphenol, Antioxidant and Antibacterial Activities of Black Mate Tea