Characterization of Edible Oils Using Total Luminescence Spectroscopy

Abstract

Total luminescence spectroscopy was used to characterise and differentiate edible oils and additionally, to control one of the major problems in the oil quality--the effect of thermal and photo-oxidation. We studied several vegetable oils available on the Polish market, including soybean, rapeseed, corn, sunflower, linseed and olive oils. Total luminescence spectroscopy measurements were performed using two different sample geometries: front-face for pure oil samples and right-angle for transparent samples, diluted in n-hexane. All the samples studied as n-hexane solutions exhibit an intense peak, which appears at 320 nm in emission and 290 nm in excitation, attributed to tocopherols. Some of the oils exhibit a second long-wavelength peak, appearing at 670 nm in emission and 405 nm in excitation, belonging to pigments of the chlorophyll group. Additional bands were present in the intermediate range of excitation and emission wavelengths; however, the compounds responsible for this emission were not identified. The front-face spectra for pure oils included chlorophyll peaks for most samples, and some additional peaks in the intermediate range, while the tocopherol peaks were comparatively less intense. The results presented demonstrate the capability of the total luminescence techniques to characterise and differentiate vegetable oil products, and additionally, to characterize the effect of thermal and photo-oxidation on such products. In the photo-oxidation experiments, special attention was paid to possible involvement of singlet oxygen. Experiments were done to monitor the highly specific O2(1delta(g)) --> O2(3sigma(g)-) singlet oxygen emission at 1270 nm. Thus, total luminescence spectroscopy presents an interesting alternative to time-consuming and expensive techniques such as gas or liquid chromatography, mass spectrometry and other methods requiring wet chemistry steps.

Analysis of Olive Oils by Fluorescence Spectroscopy: Methods and Applications

“…This assignment has been confirmed by several observations. Firstly, it was shown that a similar band appears in various vegetable oils, either cold-pressed or refined, and not only in olive oils (Sikorska et al, 2004). Olive oils contain considerable amounts of phenolic compounds, with their concentrations significantly reduced in refined oils.…”

“…The effect of concentration on the total and synchronous fluorescence spectra of vegetable oils including olive oils was reported by Sikorska et al (2004;.…”

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

“…Spectroscopic methods could be also used for detecting oil adulteration and for using in oil routine analyses. 15 Sikorska et al [15][16] reported the applicability of total luminescence spectroscopy for characterization of vegetable oils and monitoring their changes during photo and auto oxidation.…”

“…Spectroscopic methods could be also used for detecting oil adulteration and for using in oil routine analyses. 15 Sikorska et al [15][16] reported the applicability of total luminescence spectroscopy for characterization of vegetable oils and monitoring their changes during photo and auto oxidation.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. Then, 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.…”

Evaluation of α-tocopherol in virgin olive oil by a luminescent method

“…An alternative for tocopherol determination is the l GRASAS Y ACEITES, 60 (4), JULIO-SEPTIEMBRE, 336-342, 2009 . The ability of virgin olive oil to emit fluorescent radiation is partially due to the presence of chlorophylls, pheophytins and tocopherols (Galano Diaz et al, 2003;Sikorska et al, 2004). Thus, spectrofluorimetric methods have been used to distinguish diverse edible oils (Sikorska et al, 2005) to characterize olive oil designations (Nicoletti, 1990) and to detect the presence of hazelnut oil in olive oil (Sayago et al, 2004).…”