Calibration of Squalene, p-Cymene and Sunflower Oil as Standard Oxidizable Substrates for Quantitative Antioxidant Testing

The autoxidation kinetics of stripped sunflower oil (SSO), squalene (SQ) and p-cymene (p-C) initiated by 2,2′-azobis(isobutyronitrile) at 303 K were investigated under controlled conditions by differential oximetry so to build reference model systems that are representative of the natural variability of oxidizable materials, for quantitative antioxidant testing. Rate constants for oxidative chain-propagation kp and chain-termination 2kt and the oxidizability (kp/√2kt) were measured using 2,6-di-tert-butyl-4-methoxyphenol, 2,2,5,7,8-pentamethyl-6-chromanol, BHT, and 4-methoxyphenol as reference antioxidants. Measured values of kp (M-1s-1) / 2kt (M-1s-1) / oxidizability (M-1/2s-1/2) at 303K in chlorobenzene were 66.9 / 3.45106 / 3.6×10-2, 68.0 / 7.40106 / 2.5×10-2, and 0.83 / 2.87106 / 4.9×10-4, respectively for SSO, SQ and p-C. Quercetin, magnolol, caffeic acid phenethyl ester and 2,4,6-trimethylphenol, were investigated to validate calibrations. The distinctive usefulness of the three substrates in testin...