Desenvolvimento de método analítico para determinação da capacidade antioxidante de óleos comestíveis utilizando sistema BIA com detecção amperométrica

Abstract

This work reports an electroanalytical method for the determination of antioxidant capacity of edible oils. This method uses a disposable screen-printed graphitic electrode (SPGE) coupled with a batch-injection analysis cell (BIA), based on the measurement of the consumption of 2,2-diphenyl-1-picrylhydrazyl (DPPH). The SPGE’s used in this work are organic-resistant electrodes and thus compatible with oil samples and organic solvents used to dissolve DPPH. The reaction between DPPH and oil samples or antioxidant standard, such as α-tocopherol, caffeic acid and butyl-hydroxitoluene (BHT), was performed by the reaction of a mixture containing 25 µL of sample and 5.0 mL of DPPH for 1 hour protected from light. A micropipette controlled the release (193 µL s-1) of sample (150 µL) upon the working electrode immersed in an electrolytic solution of 1:1 v/v ethanol/methanol containing 0.05 mol L-1 LiCl contained in the BIA cell. The remaining DPPH was amperometrically detected at +0.1 V (vs. pseudo AgCl). The antioxidant capacity (percentage of DPPH scavenging and mg equivalent of tocopherol in the samples) was obtained using the proposed and spectrophotometric methods. The results were in agreement according to paired t-test (confidence level of 95%). Moreover, the method is precise (RSD = 2.3%; n=12), fast (180 h-1), presents low detection limit of DPPH (1 µmol L-1), and allows on-site analysis.