Frying stability time of olive oils estimated from the oxidative stability index

Six refined olive oil samples were characterized to have wide ranges of compositional indicators (the ratio between monounsaturated and polyunsaturated fatty acids = 3.9–9.6; peroxide value = 1.3–7.0 meq/kg; acid value = 0.4–0.6 mg/g; total tocopherols = 150–459 mg/kg; total phenolics = 11–39 mg/kg). Oxidative stability index (OSI) and frying stability time (the time required to reach a total polar compounds, TPC, of 25%, a conjugated diene value, CDV, of 25 mmol/l, and a carbonyl value, CV, of 47 µmol/g) of the olive oils were monitored under two thermal (Rancimat at 110–140 °C) and frying (at 180 °C) processes, respectively. The values of OSI ranged from 7.1 to 16.9 h at 110 °C, which significantly decreased to 0.9–1.9 h at 140 °C. Frying stability times were calculated to be 38.3–56.6 h, 25.6–64.1 h, and 32.4–55.3 h in terms of TPC, CDV, and CV, respectively. The greatest correlations (R2 ≥ 0.97) were obtained between the OSI at 110 °C and the frying stability times. The CV-based frying stability times provided the highest correlations at all temperatures used in the thermal process.