Autoxidation in milk rich in linoleic acid I. An objective method for measuring autoxidation and evaluating antioxidants

Autoxidation was studied in milk obtained from cows fed on formaldehyde-treated casein-safflower oil supplement. The fat of this milk contained high levels of linoleic acid. A rapid disappearance of dissolved oxygen (DO), measured by using a oxygen electrode, from milk samples stored at 0 degrees C in tubes without head-space, coincided with the development of oxidized flavours detected organoleptically. A correlation coefficient of 0.9 with 69 degrees of freedom (P smaller than 0.001) was obtained between the amount of DO disappearing and the taste panel scores for oxidized flavours. Butylated hydroxyanisole, sesamol, nordihydroguaiaretic acid, ethoxyquin, or butylated hydroxyanisole with propylgallate or tocopherols, when added in emulsified form to the milk at the rate of 10-15 mg/l milk checked the development of oxidized flavours and the rapid disappearance of DO. Other antioxidants tested were either ineffective or imparted off-flavours to milk. Samples of mare's milk neither developed oxidized flavours nor showed rapid disappearance of DO over a test period of 8 d. The oxygen electrode provides a convenient and sensitive method for studying autoxidation and evaluating antioxidants in milk.