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

Abstract

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 °C; however several authors have reported oxidative stability values at different temperatures higher than 98 °C (110 °C, 120 °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 °C. A mathematical model is presented to transform the induction period inter-temperatures (98–140 °C). The results suggested 110 °C as the more adequate temperature since the analysis time was shortened by 63% compared to induction period obtained at 98 °C; the inter-conversion 98–110 °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 °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.