Effects of α‐Tocopherol on Oxidative Stability and Phytosterol Oxidation During Heating in Some Regular and High‐Oleic Vegetable Oils

Abstract The first part of this study evaluated oxidative stability in high‐oleic rapeseed oil, palm olein, refined olive oil, low erucic acid rapeseed oil and sunflower oil. The results showed oxidative stability in the order: palm olein > high‐oleic rapeseed oil > refined olive oil > low erucic acid rapeseed oil > sunflower oil, as determined by the Rancimat method. Addition of α‐tocopherol at high levels of up to 0.2% increased the oxidative stability of refined olive oil, whereas the opposite effect was generally observed in the other oil samples. In the second part of the study, high‐oleic rapeseed oil, palm olein, refined olive oil and refined olive oil containing 0.2% α‐tocopherol were heated for 3, 6, 9 and 12 h at 180 °C. The peroxide and p‐ anisidine values generally increased over time in the samples, including olive oil containing 0.2% α‐tocopherol. High‐oleic rapeseed oil contained the highest amount of total sterols and total phytosterol oxidation products (POPs), but during heating the total POPs content increased moderately (~10%), in contrast to the threefold increase after 12 h of heating in palm olein and refined olive oil. Very high levels of 6‐hydroxy derivatives of brassicastanol, campestanol and sitostanol and of 7‐ketobrassicasterol were observed in high‐oleic rapeseed oil samples. Addition of 0.2% α‐tocopherol during heating significantly decreased POPs formation in refined olive oil ( P < 0.05).