Studies On Effects Of Phospholipids And Free Fatty Acids On Formation Of Smoke And Oxidation Stability In Vegetable Oils

In order to understand the effect of phospholipids and free fatty acids(oleic acid, linoleicacid and linolenic acid) on smoke point, oil smoke and oxidation stability of vegetable oil.The paper used saturated vegetable oil (palm oil); monounsaturated vegetable oil (tea seed oil);double unsaturated vegetable oil (sunflower seed oil) and polyunsaturated vegetable oil(linseed oil) to study the effects of phospholipids and free fatty acids on the smoke point,smoke and oxidation stability of vegetable oils, finally to lay the foundation for thedevelopment of high quality edible oil.Through analyzing the physical and chemical properties of four type vegetable oils. Wefound that palm oil had the highest content of saturated fatty acid (palmitic acid content is46.36%), the smoke point was the highest and the oxidation stability was the best. Linseed oilhad the maximum amount of unsaturated fatty (linolenic acid content is45.33%), the smokepoint was the lowest and the oxidation stability was the worst.We studied the effects of the addition of phospholipids and free fatty acids on the smokepoint of four type vegetable oils, and analyzed the difference of smoke point of different oils.The results show that phospholipids and free fatty acids can decrease the smoke point ofvegetable oils, regression analysis shows that it had a good linear relationship between theamount of phospholipids or free fatty acids and the smoke point of vegetable oil. After addingphospholipids, oleic acid, linoleic acid and linolenic acid, the smoke point of palm oilchanged obviously (the slope are-0.1387,-0.1353,-0.1518and-0.2024respectively); then teaseed oil (the slope are-0.1072,-0.1004,-0.1206and-0.1650respectively); then sunflowerseed oil (the slope are-0.092,-0.0896,-0.1077and-0.1335respectively); linseed was theleast (the slope are-0.0727,-0.0688,-0.0809and-0.1132respectively).We studied the changes of main chemical composition of oil smoke after addingphospholipids and free fatty acids. The results show that after adding phospholipids, oleic acid,linoleic acid and linolenic acid, the main smoke compositions of every type of vegetable oilhad no significant change, but there was a decrease of the content of high molecular weightsubstances and an increase of the content of small molecular weight substances. Such as2-decenal and2-undecylenic aldehyde content reduced while2,4-heptyldiene aldehydecontent increased gradually in palm oil;2-undecylenic aldehyde content reduced whilenonanal and2-heptenal content increased gradually in tea seed oil;2,4-nonadienal contentreduced while hexanal content increased gradually in sunflower seed oil; Nonanal contentreduced while2,4-heptyldiene aldehyde content increased gradually in linseed oil.Then we studied the effects of the addition of phospholipids and free fatty acids on theoxidation stability of four type vegetable oils, and analyzed the difference of oxidationstability of different oils. The results show that phospholipids can increase the oxidativeinduction time while free fatty acids can decrease the oxidative induction time of vegetableoils, regression analysis shows that it had a good linear relationship between the amount ofphospholipids or free fatty acids and the oxidative induction time of vegetable oil. Theoxidative induction time of palm oil changed obviously (the slope are0.0025,-0.0044, -0.0053and-0.0064respectively); then tea seed oil (the slope are0.0009,-0.0010,-0.0014and-0.0023respectively); then sunflower seed oil (the slope are0.0004,-0.0007,-0.0009and-0.0013respectively); linseed was the least (the slope are0.00007,-0.0002,-0.0002and-0.0003respectively).Finally, through analyzing oxidation kinetics of four type vegetable oils, we exploredthe effect of phospholipids and free fatty acids on the thermal oxidation decompositionmechanism of vegetable oils. The results show that the palm oil had the highest oxidativedecomposition activation energy (195.01kJ/mol), while the linseed oil had the lowestoxidative decomposition activation energy (80.83kJ/mol). The oxidative decompositionactivation energy of vegetable oils reduced after adding phospholipids and free fatty acids,and along with the order of phospholipids, oleic acid, linoleic acid and linolenic acid, thereduction of the oxidative decomposition activation energy became larger. The activationenergy of palm oil, tea seed oil, sunflower seed oil and linseed oil decreased by up to25.38kJ/mol、22.49kJ/mol、16.81kJ/mol and5.63kJ/mol. Because of the decrease of the oxidativedecomposition activation energy, the oxidative decomposition of vegetable oils became easyto happen. So the smoke point became lower; the oxidation stability became worse and thehigh molecular weight substances decomposed to small molecular weight substances in oilsmoke.