Thermal oxidization study of vegetable oils by ultraviolet-visible spectroscopy

Abstract

The reuse of vegetable oils after successive heating requires research of quality tests, because the oil used in frying causes loss of initial quality and is harmful to health. In this work was studied whether some vegetable oils used in the preparation food are appropriate when subjected to thermal oxidization, by ultraviolet-visible spectroscopy analysis (UV-vis). The iodine value, saponification index and acidity value of each sample in natura originally were determined by hydrogen nuclear magnetic resonance (1H-NMR). Then, the samples were subjected to a separate system of heating in two phases (Phases 1 and 2): in  Phase 1, 200 mL of each sample in natura was heated to 180 °C 4h/day for seven days and in Phase 2 the same amount of each sample in natura was heated to 180 °C 8h/day for ten days. The samples were reviewed daily, at each end of heating, by UV-vis spectroscopy. The results of the iodine value, saponification index and acidity value by 1H-NMR calculations for the samples in nature were within the values set up by ANVISA for edible oils, as well as the analyses by UV-vis demonstrated that vegetable oils thermal oxidized deteriorate rapidly as seen in the batocromic displacement of the samples heated and increasing the absorption intensity in the λ 230 nm place.