2.4. Oil quality
Acidity, peroxide value (PV), and extinction coefficient (K270 and K232) determination were carried out following the analytical methods described in the EEC/2568/91 standard of the Commission of the European Community (2003). Acidity and PV are expressed in % oleic acid and mili-equivalents of active oxygen per kilogram of oil (mEqO2/kg) respectively, and extinction coefficients K270 and K232 are the specific extinction of a 1% (w/v) solution of oil in 2,2,4-trimethylpentane in 1 cm cell path length.
Oxidative stability of each sample was determined as the induction period (IP) measured in hours (h) recorded with a Rancimat 743 apparatus (Metrohm, Switzerland), using 3 g of oil. Samples placed into Rancimat standard tubes were subjected to the normal operation of the test by heating at 110 °C with an air flow of 20 L/h.