Determination of tocopherol in oxidized fats. Interference from heat‐formed reducing substances in highly oxidized fats

Summary and Conclusions By application of a heating method to determine tocopherol in oxidized fats it was shown that polymeric reducing substances were produced when fats have a peroxide value exceeding 100. By comparison with a chromatographic method to remove peroxides it was shown that the interference in determining tocopherol from these heat‐produced reducing substances was negligible at peroxide levels lower than 100. It is concluded that the heating method is satisfactory within the peroxide range (0–100) most important in oxidative and flavor‐stability studies of edible oils. The chromatographic method for removing peroxides can be relied upon for determining tocopherol in more highly oxidized fats as well as in methyl esters of fatty acids which are distillable under conditions of the heating method. The appearance of reducing substances in heated oxidized fats is related to the peroxides present in the fats prior to heating. It is accompanied with an increase in browning, viscosity, acid, and carbonyl values of the fats and with a decrease in iodine values. The polymeric material from heated‐oxidized methyl esters of unsaturated fatty acids has been separated by vacuum distillation and chromatography on silicic acid. It is believed to be principally dimeric in nature.