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Electrochemical detection of polyphenols in food samples

Polyphenols are the significant plant compounds with antioxidant activity and are the subject of increasing scientific interest because of their beneficial effects on human health (anti- carcinogenic, anti-mutagenic, anti- inflammatory etc.). The most important polyphenols are the ones which come from routine consummation of fruits and vegetables and it is important to detect concentrations of polyphenols in real samples. Protocatechuic acid and p-hydroxybenzoic acid are natural polyphenols mostly found in green tea, acai oil, plums, grapes, coconut and wine. So, the main goal of this study was to detect protocatechuic acid and p-hydroxybenzoic acid in model systems and in real samples. The measurements were performed in a Faraday cage using potentiostat/galvanostat (PalmSens) controlled by PSTrace 1.2. software. The three electrode system consisted of a glassy carbon working electrode, Ag/AgCl reference electrode and a platinum wire counter electrode. The system was purged with high purity argon (fiAr= 99.999 %) before each measurement. Cyclic voltammograms of both polyphenols showed one oxidation and one reduction peak which correspond to oxidation of hydroxyl group(s) and reduction of oxidation product of investigated antioxidants. The oxidation of both polyphenols was diffusion controlled and pH dependent. Differential pulse voltammograms have shown that the highest oxidation peak current was around pH = 4 for protocatechuic acid and around pH = 6 for p-hydroxybenzoic acid, while it decreased in more acidic and alkaline medium. It was also determined that the anodic peak current of investigated polyphenols linearly increase with the increase of their concentration in the concentration range from 1 M to 600 M. Both polyphenols were detected in real samples with differential pulse voltammetry where their quantity varied from 2 uM to 9 uM. The highest concentrations of investigated polyphenols were detected in wine, grapes and fruit juice while the lowest concentrations were detected in coconut milk and chicory coffee.

antioxidants, voltammetry, detection, real samples

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