Analysis of cyclopropenoid and cyclopropanoid acids in fats and oils

Abstract

AbstractThe analysis of cyclopropenoid acids may be considered, from a historical standpoint, to have started with the discovery of the Halphen test. Although this test as orginally conceived was utilized as a means of detecting adulteration of premium edible oils with cottonseed oil, it has since been shown to be a characteristic test for cyclopropenoid fatty acids and has been adapted with various modifications as a quantitative colorimetric test for these substances. More recently, spectrophotometric methods particularly in the IR region have been applied to the analysis of these substances. The 9.8 Ɓ band, characteristic of the cyclopropane, and the 9.91 Ɓ band, characteristic of the cyclopropene group, as well as the 11.0 Ɓ band, characteristic of some of the noncyclic degradation derivatives, have been utilized. Gasliquid chromatography (GLC) has been applied to the methyl esters of cyclopropanoid and hydrogenated cyclopropenoid acids. The reactivity of the cyclopropene ring toward hydrohalogens has been the basis of several analytical methods developed for use with cyclopropene acid‐containing oils. Both aqueous and nonaqueous solutions of hydrohalogens have been employed. The hydrohalogenation methods are the most precise methods currently available for these analyses but only GLC has the inherent potential of identifying the specific cyclopropenoid or cyclopropenoids involved.