Relationship of Rancimat method values at varying temperatures for virgin olive oils

Oxidative stability of VOO is widely determined by Rancimat test, an accelerated method that shortens analysis time. The most usual temperature used for Rancimat analysis is 98 degrees C; however several authors have reported oxidative stability values at different temperatures higher than 98 degrees C (110 degrees C, 120 degrees C) in order to reduce the analysis time. In this study the effect of temperature on Rancimat method for VOO analysis, measuring the method reproducibility at each temperature, has been evaluated. Method precision expressed as the relative standard deviation (RSD) was ranged from 1.14 to 5.84%, indicating that analytical method was repeatable even at 140 degrees C. A mathematical model is presented to transform the induction period inter-temperatures (98-140 degrees C). The results suggested 110 degrees C as the more adequate temperature since the analysis time was shortened by 63% compared to induction period obtained at 98 degrees C; the inter-conversion 98-110 degrees C presented low differences between theoretical value obtained from mathematical model and experimental value obtained by Rancimat apparatus. To shorten analysis time, 84 and 92% respectively, 120 and 130 degrees C can be used too; although some samples can present higher differences between theoretical and experimental induction period values because of the different oxidation mechanism at each temperature.