Comparison of a simplified,quantitative kreis test with peroxide values of oxidizing fats

Summary 1. A simplified quantitative Kreis test has been compared with peroxide numbers and iodine values during prolonged rancidification of several animal and vegetable fats. 2. The ratio of Kreis to peroxide values varied with the kind of fat and seemed to parallel its linoleic acid content. With vegetable oils containing a large amount of linoleic acid (corn and cottonseed) the intensity of color at the time of peak color development was too great to be read on the colorimeter. 3. With all fats for which accurate determinations were possible (butter, chicken, pork, and ethyl oleate), the Kreis values reached maximum and began falling off while peroxide values were still increasing. 4. Temperature of fat storage had a greater effect on the Kreis test than on the peroxide number. Increasing the temperature caused a decrease not only in the peak values obtained for the Kreis test, but also in the ratio of Kreis to peroxide values. Published as Scientific Paper No. 670, College of Agriculture and Agricultural Experiment Stations, State College of Washington, Pullman.