Chronoamperometric estimation of cognac and brandy antioxidant capacity using MWNT modified glassy carbon electrode.

Cognac and brandy components are electrochemically oxidized on multi-walled carbon nanotube modified glassy carbon electrode at 0.44 and 0.59 V in 0.1 М phosphate buffer solution pH 3.0. Voltammetric behavior of the main antioxidant constituents of cognac (ellagic and gallic acids, syringaldehyde, coniferaldehyde, vanillin, 5-hydroxymethylfurfural and furfural) has been investigated. The peak at the less positive potential of cognacs is caused by oxidation of gallic acid as well as syringaldehyde- and coniferaldehyde. The second peak corresponds to ellagic acid oxidation. One-step chronoamperometry at 0.59 V for 75 s has been applied for the cognac and brandy antioxidant capacity (AOC) evaluation. Ellagic acid, being the main antioxidant of cognac, has been used as a reference substance. The chronoamperometric response of ellagic acid is linear in the range of 0.66-52.8 µM with the limit of detection and quantification at 0.19 and 0.63 µM, respectively. AOC in ellagic acid equivalents per 100mL of cognac and brandy for different denominations (11 cognacs and 11 ordinary and vintage brandies) has been estimated. AOC of cognacs and brandies increases with the age of the beverages. Positive correlations (r=0.9134-0.9703) with common parameters characterizing antioxidant properties of beverages, in particular antiradical activity, total phenolics content, total antioxidant capacity and ferric reducing power have been observed.