Thumbnail Image
Publication

A FRAP Assay at pH 7 unveils Extra Antioxidant Activity from Green, Black, White and Rooibos Tea but not Apple Tea

Owusu-Apenten, Richard K.
; 
Wong, C. W.
; 
Cheung, W. S. M.
; 
Lau, Y. Y.
; 
Bolanos de la Torre, Angelica A. S.
Advisors
Editors
Other Contributors
Affiliation
University of Chester, University of Ulster
EPub Date
Publication Date
2015-06-26
Submitted Date
Collections
Clinical Sciences and Nutrition
Show all metadata
Files
Thumbnail Image
Main article
Adobe PDF, 582.12 KB
Other Titles
Abstract
Aim: Realization of a ferric reducing antioxidant power (FRAP) assay at neutral pH and re-evaluation of tea antioxidant activity for comparisons with the standard FRAP assay. Method: A FRAP assay at neutral pH utilized ferrozine (7.3-(2-Pyridyl)-5, 6-diphenyl-1, 2, 4-triazine-4’, 4’’-disulfonic acid;ferrozine) dye in conjunction with Tris-HCl buffer (0.1M. pH 7.0) with 280 µl of regent addition to 20 µl of tea infusions and absorbance measurements at 562 nm with a microplate reader. Results: The microplate ferrozine FRAP assay (mFzFRAP) gave linear calibrations for ascorbic acid, gallic acid, ammonium ferrous sulphate, (AFS), trolox, cysteine and glutathione (R2 = 0.998 -1.000) with molar absorptivity (measures of sensitivity) similar to literature values. The analytical precision was 5-7% and the minimum detectable concentrations (MDC) were 1.4- 2.8 µM (0.4-0.8 nanomoles). Discussion: Values for FRAP were higher at pH 7.0 compared to pH 4.0 for gallic acid, ascorbic acid, glutathione, and cysteine possibly due to their ionization at high pH. The assay sensitivity for AFS and trolox were unchanged at pH 4.0 and pH 7.0. When assayed at pH 7 the water infusions from green tea, black tea, white tea, and rooibos tea had 200-360% antioxidant activity normally observable at low pH. Conclusion: A FRAP assay at pH 7 unveils extra antioxidant activity for green, black, white and Rooibos teas compared to values from the standard TptzFRAP (pH 3.6) method. As a recommendation, the antioxidant activity of teas and other herbal preparations should be re-evaluated over a wide pH range.
Citation
Wong, C. W., Cheung, W. S., Lau, Y. Y., Bolanos de la Torre, A. A. S. & Owusu-Apenten, R. (2015). A frap assay at pH 7 unveils extra antioxidant activity from green, black, white and rooibos tea but not apple tea. Food and Nutrition Report, 1(1), 16-23.
Publisher
Verizona
Journal
Food and Nutrition Report
Research Unit
URI
http://hdl.handle.net/10034/621964
DOI
10.24218/fnr.2015.03
PubMed ID
PubMed Central ID
Type
Article
Language
en
Description
Series/Report no.
ISSN
2059-8564
EISSN
ISBN
ISMN
Gov't Doc
Test Link
Sponsors
Additional Links
http://verizonaonlinepublishing.com/FoodandNutrition.aspx