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

Yuk Man Chan, Nga Kwan Cheng, P Nigam, R.K. Owusu-Apenten

Research output: Contribution to journalArticle

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 Antioxidant Capacity (AAEAC) was grater 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.
Original languageEnglish
Pages (from-to)1-8
JournalJournal of Applied Life Sciences International
Volume6
Issue number2
Early online date22 Jun 2016
DOIs
Publication statusE-pub ahead of print - 22 Jun 2016

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Keywords

  • Radical quenching
  • ABTS
  • tea
  • gallic acid
  • ascorbic acid
  • TEAC value.

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