Themooxidative and Autoxidative Stability of Wheat Germ Oil

Abstract

A stability of wheat germ oil against thermal oxidation and autoxidation was compared with soybean, cottonseed and corn oils. The nutritionally deleterious dimer glycerides produced in heated oils were also determined. Furthermore, the composition of unsaponifiable matter in wheat germ oil and a presence of antioxidative compounds except tocopherols were investigated. Thermally oxidized oils were prepared by heating fresh oils at 180±2°C for 8 hours a day for 6 days. Several chemical characteristics of the thermally oxidized oils indicated that a stability of wheat germ oil against thermal oxidation was superior to soybean oil but not good as cottonseed and corn oils. The stabilities of fresh and thermally oxidized oils against autoxidation in oven test were almost similar to those of thermal oxidation. There was no significant difference of the contents of dimer glycerides among the thermally oxidized oils and also the quantities produced in those oils seemed to be negligible for deleterious effect on nutrition. Major component in unsaponifiables of wheat germ oil was sterols and tocopherols were present in minor quantity. However, the contents of total, and α-and β-tocopherols in wheat germ oil were the highest when compared with other vegetable oils. Presence of antioxidative component other than tocopherols in unsaponifiables of wheat germ oil was not recognized. Wheat germ oil is not suitable for frying oil because of its less thermal oxidative stability. Wheat germ oil contains high quantity of linoleic acid, and physiologically active α-and β-tocopherols, so it is preferable to ingest this oil as fresh.