Electrochemistry-based determination of pungency level of hot peppers using the voltammetry of microparticles

The electrochemical behaviour of capsaicin on a paraffin-impregnated graphite electrode (PIGE) was investigated using square-wave (SWV) and cyclic voltammetry (CV) in a wide range of pH values (2.0–11.0) and potential scan rates. The electrochemical oxidation of capsaicin is an irreversible process and occurs in a complex, pH dependent mechanism. In electrolytes with 2 ≤ pH ≤ 10 oxidation involves the transfer of two electrons and two protons, followed by chemical transformation and the formation of a product which undergoes a further reversible redox reaction. However, at pH close to pKa the product of two-electron electrochemical oxidation of capsaicin dissolves into the electrolyte.Analysis of microparticles of dry ground pepper samples immobilized on the surface of PIGE was performed using SWV under optimal experimental conditions of pH 11, pulse amplitude of 50 mV, frequency of 150 Hz, and step potential of 2 mV. The presence of capsaicin in samples was registered with good precision and sensitivity. The proposed methodology exploits the current intensity of capsaicinoids in pepper samples in order to classify samples according to their pungency. A strong positive correlation was observed between the measured peak currents for capsaicinoids in pepper samples and the average of Scoville heat units reported in the literature (R = 91.3%).