Evaluation of tests for rancidity in edible packaged oils

Abstract

Organoleptic tests, in spite of their limitations, were the most satisfactory methods of determining the quality of corn and cottonseed oils which had aged in sealed containers. The chemical and physical tests used in this investigation were influenced more by storage conditions, such as exposure to light or the presence of air, than by the actual organoleptic state of the oil. Changes in the methylene blue fading time of an oil were dependent on the presence of air or a high temperature during storage. Aldehydes, as determined by the bisulfite method, increased in oils exposed to air but their formation in oils in sealed containers was very slow even with extensive development of rancidity. No significant changes in the film pressure of oil in sealed containers took place except in samples exposed to light for several months, however, aeration of an oil at 100° C. resulted in a rapid change in film pressure. Exposure to light caused the color of the oils to fade, exposure to air caused darkening, yet both factors contributed to the development of rancidity. The induction period of the oils stored in sealed containers depended upon their original peroxide value which in turn was influenced by exposure to light. Exposure of sealed samples of oil to light caused a destruction of peroxides. The chlorophyll value of oils and the fluorescence changed rapidly when they were exposed to light; however, oil could be made rancid in the absence of light with little or no significant change in its chlorophyll value. Preliminary polarographic and light transmission studies in the ultraviolet and infrared regions of the spectrum failed to reveal any changes in the oils which could be correlated with the development of rancidity.