Modified 2,2-Azino-bis-3-ethylbenzothiazoline-6-sulfonic Acid (ABTS) Method to Measure Antioxidant Capacity of Selected Small Fruits and Comparison to Ferric Reducing Antioxidant Power (FRAP) and 2,2‘-Diphenyl-1-picrylhydrazyl (DPPH) Methods

• Published in: Journal of agricultural and food chemistry 2006-02, Vol.54 (4), p.1151-1157
• Main Authors: Ozgen, Mustafa, Reese, R. Neil, Tulio, Artemio Z, Scheerens, Joseph C, Miller, A. Raymond
• Format: Article
• Language: English
• Subjects: ABTS method; antioxidant activity; antioxidants; Antioxidants - analysis; Antioxidants - chemistry; assays; Benzothiazoles; Biological and medical sciences; Biphenyl Compounds; Caffeic Acids - chemistry; Chlorogenic Acid - chemistry; DPPH method; Ferric Compounds - chemistry; food analysis; Food industries; FRAP method; Fruit - chemistry; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; grapes; Oxidation-Reduction; Picrates; raspberries; reaction kinetics; Rubus idaeus; Rubus occidentalis; small fruits; strawberries; Sulfonic Acids
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf051960d

The measurement of antioxidant capacity in fruits differs from that of other biological samples due to their low pH and very low lipophilic antioxidant capacity. In this report, we present a modified 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) method for fruits and compare its performance with the other commonly used antioxidant methods of 2,2‘-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP). The antioxidant capacity and reaction kinetics of four phenolic compounds, two antioxidant standards, and five fruits were also investigated. The modified ABTS method prepared at a pH of 4.5 with sodium acetate buffer is highly stable and easily applied to fruit samples as compared to the standard (pH 7.4) version. The measured antioxidant capacity of samples varied with the assay method used, pH, and time of reaction. Traditional antioxidant standards (trolox, ascorbic acid) displayed stable, simple reaction kinetics, which allowed end point analysis with all of assays. Of the phenolic compounds examined, chlorogenic and caffeic acids exhibited the most complex reaction kinetics and reaction rates that precluded end point analysis while gallic acid and quercetin reached stable end points. All fruit extracts exhibited complex and varied kinetics and required long reaction times to approach an end point. Because the antioxidant capacity of fruit extracts is a function of the array of individual antioxidants present, accurate comparisons among fruit samples require that reaction times be standardized and of sufficient length to reach steady state conditions and that more than one assay be used to describe the total antioxidant activity of fruit samples. Keywords: Natural antioxidants; polyphenols; phenolics; ABTS; phytonutrients; phytochemicals; oxidative stress; berries; black raspberry; red raspberry; blackberry; strawberry; grape; free radicals; antioxidant assay; dietary antioxidants