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Effect of pH on the Radical Quenching Capacity of Tea Infusions Using the ABTS•+ Assay

Chan, Yuk Man
; 
Cheng, Nga Kwan
; 
Nigam, Poonam S.
; 
Owusu-Apenten, Richard K.
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Affiliation
University of Chester, University of Ulster
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2016-06-22
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Clinical Sciences and Nutrition
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Abstract
Aims: The aims of this study were to assess the impact of pH on the free radical quenching activity of tea infusions using a modified 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assay and three antioxidant compounds as reference. Study Design: In-vitro method. Place and Duration of Study: Faculty of Life and Health Science, School of Biomedical Sciences, Ulster University, UK. From Sept 2014 and May 2016. Methodology: Free radical quenching capacity of tea (Earl grey, black tea, Ceylon tea, & green tea) infusions were investigated using persulfate activated ABTS with acetate buffer (pH 4.5) or phosphate buffer saline (pH 7.0) as solvent. Tests were performed using 96-well microplates, 20 µl of sample and 280 µl of ABTS reagent, and calibrated using ascorbic acid, trolox or gallic acid as reference antioxidants. Results: Gallic acid free radical quenching was pH dependent and unsuitable as reference. The free radical quenching capacity of trolox and ascorbic acid was not significantly different at pH 4.5 and pH 7.0. The radical quenching capacity of tea infusions expressed as Trolox Equivalent Antioxidant Capacity (TEAC) or Ascorbic Acid Equivalent Antioxidant Capacity (AAEAC) was greater by 50-300% at pH 7 compared to pH 4.5. Conclusion: The modified ABTS assay is suitable for examining the influence of pH on free radical quenching ability of tea samples. Gallic acid was not a suitable reference compound. The radical quenching capacity of tea infusions increases with rising pH.
Citation
Chan, Y. M., Cheng, N. K., Nigam, P. S., & Owusu-Apenten, R. (2016). Effect of pH on the Radical Quenching Capacity of Tea Infusions Using the ABTS• Assay. Journal of Applied Life Sciences International, 6(2), 1-8.
Publisher
SCIENCEDOMAIN International
Journal
Journal of Applied Life Sciences International
Research Unit
URI
http://hdl.handle.net/10034/621910
DOI
10.9734/JALSI/2016/27235
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PubMed Central ID
Type
Article
Language
en
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2394-1103
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http://www.sciencedomain.org/index.php?/abstract/15117