Muhammad Nadeem Asghar, Islam Ullah Khan,* Iram Zia, Mukhtar Ahmad# and Fahim Ashraf Qureshi
Department of Chemistry, Government College University, Lahore-54000, Pakistan
#Department of Biochemistry, Allama Iqbal Medical College, Canal Road, Lahore,
Pakistan
* Corresponding author: E-mail: iukhan@gcu.edu.pk
Office Tel: 92-042-111-000-010
Abstract
2,2’-Azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical cation
decolorization assay has been applied under
different pH conditions for the determination of trolox equivalent antioxidant
capacity (TEAC) of biological and
food samples. Due to innate nature of ABTS radical cation, it is unstable at
physiological pH. Further, its sensitivity is
also lost at acidic pH. No single method has yet claimed to cover both drawbacks
of the ABTS procedure. The present
investigation was aimed at developing an improved ABTS decolorization method for
the measurement of antioxidant
activity of human plasma and herbal extracts with greater stability and
sufficient sensitivity. A relatively stable ABTS
radical cation was generated through a reaction between ABTS and potassium
persulfate in the presence of sodium acetate
buffer at pH 6.5 (20 mM). The electron or hydrogen atom transfer from
antioxidative components of plasma or herbal
extracts reduced the radical cation. Standard antioxidants like trolox,
butylated hydroxyanisol (BHA), butylated
hydroxytoluene (BHT) and ascorbic acid demonstrated stable end-point readings
showing a promising aspect of determination
of total antioxidant activity (TAA) of all the other samples with reference to
these indicators. The modified assay
proved to be highly reproducible. TEAC values for plasma samples ranged between
1.410–2.025 mM with mean
percent relative standard deviation (% RSD) 1.64 and between 1.72–1.98 with mean
% RSD 1.27 for older and modified
ABTS assays, respectively. The efficacy of the assay was ascertained further by
determining antioxidant activity of
organic and aqueous extracts of Cuscuta reflexa and Terminalia arjuna.
Keywords: ABTS radical cation, antioxidant activity, TEAC, plasma, potassium persulfate.