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

CW Wong, WSM Cheung, YY Lau, AAS Bolanos de la Torre, Richard Owusu-Apenten

Research output: Contribution to journalArticle

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. pH7.0) 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 sensitivityfor 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 activitynormally 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 arecommendation, the antioxidant activity of teas and other herbal preparations should be re-evaluated over a wide pH range.
LanguageEnglish
Pages1-8
JournalFood and Nutrition Report
Volume1
Issue number1
Publication statusPublished - 26 Jun 2015

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Assays
Antioxidants
Ferrozine
Gallic Acid
Ascorbic Acid
Glutathione
Cysteine
Tea
hydroquinone
Plant Preparations
Ionization
Buffers
Coloring Agents
Calibration
Acids
Water

Keywords

  • Tea
  • Antioxidant activity
  • microplate
  • FRAP
  • Ferrozine
  • pathlength calibration

Cite this

Wong, CW., Cheung, WSM., Lau, YY., Bolanos de la Torre, AAS., & 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), 1-8.
Wong, CW ; Cheung, WSM ; Lau, YY ; Bolanos de la Torre, AAS ; Owusu-Apenten, Richard. / A FRAP Assay at pH 7 unveils Extra Antioxidant Activity from Green, Black, White and Rooibos Tea but not Apple Tea. In: Food and Nutrition Report. 2015 ; Vol. 1, No. 1. pp. 1-8.
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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. pH7.0) 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 sensitivityfor 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 activitynormally 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 arecommendation, the antioxidant activity of teas and other herbal preparations should be re-evaluated over a wide pH range.",
keywords = "Tea, Antioxidant activity, microplate, FRAP, Ferrozine, pathlength calibration",
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Wong, CW, Cheung, WSM, Lau, YY, Bolanos de la Torre, AAS & 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, vol. 1, no. 1, pp. 1-8.

A FRAP Assay at pH 7 unveils Extra Antioxidant Activity from Green, Black, White and Rooibos Tea but not Apple Tea. / Wong, CW; Cheung, WSM; Lau, YY; Bolanos de la Torre, AAS; Owusu-Apenten, Richard.

In: Food and Nutrition Report, Vol. 1, No. 1, 26.06.2015, p. 1-8.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A FRAP Assay at pH 7 unveils Extra Antioxidant Activity from Green, Black, White and Rooibos Tea but not Apple Tea

AU - Wong, CW

AU - Cheung, WSM

AU - Lau, YY

AU - Bolanos de la Torre, AAS

AU - Owusu-Apenten, Richard

N1 - Citation:Wong CW, Cheung WSM, Lau YY, Bolanos de la Torre AAS and 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. F Nutr Reprt 1(1).

PY - 2015/6/26

Y1 - 2015/6/26

N2 - 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. pH7.0) 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 sensitivityfor 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 activitynormally 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 arecommendation, the antioxidant activity of teas and other herbal preparations should be re-evaluated over a wide pH range.

AB - 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. pH7.0) 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 sensitivityfor 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 activitynormally 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 arecommendation, the antioxidant activity of teas and other herbal preparations should be re-evaluated over a wide pH range.

KW - Tea

KW - Antioxidant activity

KW - microplate

KW - FRAP

KW - Ferrozine

KW - pathlength calibration

M3 - Article

VL - 1

SP - 1

EP - 8

JO - Food and Nutrition Report

T2 - Food and Nutrition Report

JF - Food and Nutrition Report

SN - 2059-8564

IS - 1

ER -

Wong CW, Cheung WSM, Lau YY, Bolanos de la Torre AAS, Owusu-Apenten R. 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. 2015 Jun 26;1(1):1-8.