Abstract
Antioxidants are a very important class of food additive. They play the fundamental role of retarding oxidation reactions, i.e. preventing rancidity, stabilize food color and appearance. Although their functional role is well-established, less clear is their mechanism of action. Consequently, it is important to test antioxidants in a wide range of conditions such as concentrations, pHs, solvents and/or substrates. The need to develop high throughput system is driving a renovated interest on the use of electrochemical methods. This work investigates the reactivity of individual antioxidant with the free radicals generated by 2,2'-azobis(isobutironitrile) (AIBN). The consumption of antioxidants was followed by cyclic voltammetry. The fitting of such decay with a kinetic model yielded the rate constant 𝑘𝑘𝑑𝑑 of radical formation and the rate constant 𝑘𝑘𝑖𝑖𝑖𝑖ℎ of radical inhibition exerted by each antioxidant. The antioxidant efficiency was defined as the ratio between 𝑘𝑘𝑖𝑖𝑖𝑖ℎ and 𝑘𝑘𝑑𝑑. The following ranking of antioxidants was obtained: α-tocopherol>> catechin>> retinyl acetate>> hydroxytyrosol>> oleuropein >> caffeic acid. Overall, the approach shows the effectiveness of cyclic voltammetry to investigate the kinetic rates at which antioxidants react with radicals. The approach was implemented for characterizing commercial edible oils: EVOO, old EVOO (12 months of storage), VOO and SOO. According to the results, the peroxyl scavenging activity was highest in the EVOO samples compared to VOO and SOO. This was confirmed by the DPPH assay and HPLC-MS analysis. However, it should be also recognized that this approach needs relatively long experimental times (i.e. several hours). In general, long experimental times are not attractive when redox species prone to passivate the working electrode are investigated. As the follow up work, we also used styrene to investigate the possibility to enhance this proposed approach by speeding up the time of analysis by understanding the impact of solvent and temperature on the rate constants, and found effective. But, further investigation is required to conclude it.