Effect of β-sitosterol in the antioxidative activity of oxidized lipid–amine reaction products

Phosphatidylethanolamine (PE), phosphatidylcholine (PC), lysine (Lys), and mixtures of them were tested for activity in a polar compound-stripped olive oil (SOO) and in the same oil after addition of 1500 ppm of β-sitosterol (phytosterol-added olive oil, PAO) to evaluate the role of phytosterols in the antioxidant activity of oxidized lipid–amine products. None of the added compounds protected either SOO or PAO, when tested alone at 0–400 ppm. However, mixtures of PE/Lys and PC/Lys (100/300, 200/200, and 300/100 ppm) significantly increased the induction periods of both oils. Furthermore, there was a synergism between the phospholipids and Lys, which was a consequence of the reaction between the carbonyl compounds produced in the oxidation of the phospholipid fatty acid chains and the amino group of Lys. Some of these carbonyl–amine reaction products were determined by gas chromatography–mass spectrometry after converting them into volatile derivatives. In addition, stepwise multiple regression analysis demonstrated the relationship between the induction periods and the formed products. However, the contribution of carbonyl–amine reaction products to oil stability also depended on the type of oil, therefore suggesting a role of β-sitosterol in the antioxidative activity of the compounds produced by carbonyl–amine reactions. This contribution was also confirmed by the higher synergism observed for PE/Lys and PC/Lys mixtures in PAO than in SOO.