Antioxidant Capacity Of Spices Research Articles

Determination of the antioxidant capacity of the micellar extracts of spices in Brij® 35 medium by differential pulse voltammetry

It was established that the micellar extracts of spices are electrochemically active on a glassy carbon electrode modified with cerium dioxide nanoparticles in a 0.02 M Brij® 35 in the presence of a phosphate buffer solution (pH 7.4) under the conditions of differential pulse voltammetry. The number of oxidation steps and their potentials vary over a wide range depending on the type of spice. A number of the oxidation peaks of the micellar extracts of spices were identified based on the oxidation potentials of the following individual antioxidants: gallic acid, ferulic acid, p-coumaric acid, caffeic acid, rosmarinic acid, thymol, eugenol, vanillin, syringaldehyde, capsaicin, rutin, quercetin, catechin, tannin, and curcumin. The contribution of the main antioxidants to the amperometric response of the extracts was confirmed by the standard addition method. A procedure for the voltammetric determination of the antioxidant capacity of the extracts of spices based on the oxidation of their antioxidants was developed. The antioxidant capacity of spices was evaluated from the total area of the oxidation steps in units of gallic acid, whose analytical range, detection limit, and determination limit were 50–2490, 11.9, and 39.6 μM, respectively. Twenty types of spices were analyzed. Positive correlations of the antioxidant capacity with the ferric reducing power and the antioxidant activity (r = 0.8971 and 0.9127, respectively at r crit = 0.497) were found.

Evaluation of the antioxidant properties of spices by cyclic voltammetry

The individual antioxidants of spices (gallic and rosmarinic acids, capsaicin, thymol, and eugenol) are irreversibly oxidized at 0.88–1.25 V at a glassy carbon electrode in 0.1 M LiClO4 solution in ethanol. Corresponding electrode reactions are proposed. A linear dependence of the oxidation step area on the concentration is observed for all the analytes. The detection limits and the lower limits of quantification vary from 0.57–12 and 1.8–40 μM, respectively. Distinct steps and peaks of oxidation are observed on cyclic voltammograms of the methanolic extracts of spices; the potentials and areas of these peaks depend on the type of spice. The contribution of individual antioxidants to integral responses of spice extracts is evaluated. A method is developed for the voltammetric evaluation of the antioxidant capacity (AOC) of spices based on the oxidation of their antioxidants. The total area of the oxidation steps was selected as a parameter characterizing the antioxidant properties. The AOC of spices was expressed as a weight of gallic acid in milligrams per 1 g of a dry spice. Seventeen different spices were tested. The AOC decreases in the series of clove > juniper berries > nutmeg > cinnamon > rosemary > anise ≥ oregano > black pepper ≥ ginger ≥ basil > turmeric > red pepper ≈ bay leaf ≥ coriander ≈ red sweet pepper > cumin > caraway. A correlation between the AOC obtained by voltammetry and the total AOC, ferric reducing power, antiradical activity, and total content of phenolic compounds and these parameters with each other is found; the correlation coefficients vary in the range 0.8886–0.9615.