Abstract
Photoacoustic spectroscopy was used to obtain optical properties of edible soybean, canola and olive oils as well to evaluate the oil modifications induced by thermal treatment. The normalized photoacoustic signal intensity and its phase were independently measured as a function of wavelength of the radiation source. The oil samples were heated up to the smoke point and then for additional 30 min in order to degrade them. After, the oil samples were cooled down and photoacoustic measurements were conducted in order to obtain the absorption spectra of samples at both degraded and non-degraded conditions. Comparisons between the two conditions indicate that the degraded oil samples exhibited widening of the absorption bands in ultraviolet region of the spectra, relative to the respective non-degraded sample. Also, the peaks of those absorption bands presented a red shift.
Highlights
The photoacoustic spectroscopy (PAS) is a useful photothermal technique to obtain thermal and optical parameters of materials based on heat transfer due to absorption of radiation by the matter.[1]
PAS is a suitable technique to obtain optical absorption spectra of vegetable oils because this class of compounds is known for their physical characteristics: highly ultraviolet (UV) absorbent due to unsaturated fatty acids,[14] and light-scattering samples due to arising of polymeric compounds
This paper presented an application of a particular photothermal technique, PAS, to study optical properties of edible oils
Summary
The photoacoustic spectroscopy (PAS) is a useful photothermal technique to obtain thermal and optical parameters of materials based on heat transfer due to absorption of radiation by the matter.[1]. PAS is a suitable technique to obtain optical absorption spectra of vegetable oils because this class of compounds is known for their physical characteristics: highly ultraviolet (UV) absorbent due to unsaturated fatty acids,[14] and light-scattering samples (when degraded) due to arising of polymeric compounds. They are unsuitable for conventional optical absorption spectroscopy, i.e., absorbance spectroscopy, since they give featureless spectra (UV saturation spectra) without dilution in organic solvents. There are scarce reports on the application of photoacoustic spectroscopy technique to the analysis of edible oil samples
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