The role of acyl moiety in the formation and reactions of steryl ester hydroperoxides

Nowadays, several types of food products are fortified with plant sterols because of their cholesterol-lowering properties. Therefore, it is also important to study the oxidation behaviour of sterols and their conjugates. In the present study, the autoxidation of intact steryl fatty acyl esters was investigated by following the formation and decomposition of these esters' primary hydroperoxides. The effects of the unsaturation of the acyl moiety on the sterol oxidation were investigated by oxidising pure cholesteryl fatty acyl esters at 100 A degrees C. A previously introduced HPLC-ELSD method was further developed in order to follow the primary oxidation of steryl and acyl moieties individually. Peroxide values and secondary oxidation products of sterol were determined to confirm the obtained results and to follow further reactions. In the case of cholesteryl oleate and linoleate, the primary hydroperoxides of the steryl and acyl moieties were initially measurable at the same time point. As the unsaturation of the acyl moiety was increased, the induction period of the sterol oxidation was shortened and the rate of hydroperoxide formation increased. Moreover, the hydroperoxides started to decompose earlier. The maximum content of primary hydroperoxides was higher in cholesteryl stearate (64 mg/g) and oleate (78 mg/g) than in cholesteryl linoleate (40 mg/g). Thus, the degree of unsaturation of the acyl moiety also clearly affects the oxidation behaviour of the steryl moiety.