Monitoringthe Thermal Oxidation of Local Edible Oils by Fluorescence Spectroscopy Technique Coupled to Chemometric Methods

Abstract

In the present work, a study on the thermo-degradation of local edible oils by using fluorescence spectroscopy is conducted. Diluted unrefined palm, refined palm, cottonseed, sunflower, and soybean oils were considered. At excitation wavelength of 295 nm, fluorescence peaks were visualized at 325, 310, 415, 465, and 525 nm. A complete assignment of these different peaks is achieved by recording the 3D fluorescence spectra of the oils that were further treated by parallel factors analysis. This yielded excitation/emission peaks, which correspond according to known fluorophores in edible oils to -tocopherol (vitamin E), primary, secondary oxidation products, and carotenoid compounds. Tocopherol and oxidation products’ contents that are indicators of the vegetable oil quality are monitored at different heating temperatures and for different heating times. We showed that excitation at unique wavelength of 295 nm can be used to monitor the oil chemical composition change under heating. A positive correlation is found between the fluorescence intensity at 325 nm, 420 nm, and 465 nm and the -tocopherol content, the peroxide value, and the β + δ + γ-tocopherol content respectively. Three regression equations were obtained that can be used to make an estimate of these minor constituents as well as the peroxid value. Upon heating, a decrease of -tocopherol content accompanied by an increase in the oxidation products is observed. Refined palm, cottonseeds, and sunflower oils showed higher degree of stability against heating, whereas soybean and unrefined palm oils are unstable. A principal components analysis method provided a classification of the studied oil according to their vegetable origin. The work demonstrates the ability of fluorescence spectroscopy to help decide on the appropriate usage of edible oil.