The effect of sterols on the oxidation of edible oils

The effect of sterols on the oxidation of a triglyceride mixture, similar in composition to olive oil, has been studied at 180°C. Δ⁵-Avenasterol and fucosterol are effective as antioxidants, whilst other sterols, including cholesterol and stigmasterol, are ineffective. The antioxidant effect of Δ⁵-avenasterol increases with concentration in the range 0·01% to 0·1%.An hypothesis is presented to explain the effectiveness of the sterols as antioxidants. It is concluded that lipid free radicals react rapidly with sterols at unhindered allylic carbon atoms. Isomerisation leads to a relatively stable allylic tertiary free radical, which is slow to react further, and this interrupts the autoxidation chain.