M.Sc. 2010- Application of some Methods for Detecting Adulteration in Olive Oil.pdf
Creators: name: Almoselhy, Rania I.M.
Publisher: name: figshare
Year: 2021
Subjects: Analytical biochemistry

description: Rania Ibrahim Mohammad Almoselhy. Application of Some Methods for Detecting Adulteration in Olive Oil. Unpublished M.Sc. Thesis, Department of Food Science, Faculty of Agriculture, Ain Shams University, 2010.<br><br>This study aimed to maintain the high quality of olive oil by investigating some analytical methods as a powerful tool to determine extra virgin olive oil adulteration with relatively cheap seed and vegetable oils such as sunflower oil, corn oil and refined olive oil. The analytical methods ranged from the familiar manual physical and chemical tests such as refractive index (RI) which gives a good idea about the degree of unsaturation of the oil under investigation, as well as its correlation with iodine value (IV); acid value (AV) as indication of free fatty acid content of the oil; peroxide value (PV) which determines the amount of primary oxidation products and UV absorbencies at 232 and 270 nm, that measure the formation of conjugated dienes and trienes, respectively due to the formation of secondary oxidation products.<br><br>The analytical methods extended to the more sophisticated instrumental methods of analysis such as chromatographic separation and determination techniques which involved gas chromatography (GC) with flame ionization detector (FID) in order to investigate the composition of the fatty acids of the oils under investigations.<br><br>Fourier Transform Infra Red (FTIR) spectroscopic determination technique was employed and applied as a potent, nondestructive and effective analytical tool to study its potency to investigate the functional groups with their relative absorbencies or transmittances according to their concentrations in samples and their characteristic fingerprints. FTIR spectroscopy was used also to determine extra virgin olive oil adulteration with sunflower, corn and refined olive oils in their binary admixtures at different concentrations of 0, 5, 10, 20, 30, 40, 50, 100%; w/w. FTIR spectral data collected in MIR range 4000-400 cm<sup>-1</sup> showed major peaks representing triglyceride functional groups which could be observed around 2925 cm<sup>-1</sup> [C–H stretching (asymmetry)], 2854 cm<sup>-1</sup> [C– H stretching (symmetry)], 1747 cm<sup>-1</sup> [C=O stretching], 1463 cm<sup>-1</sup> [C–H bending (scissoring)], 1238, 1163, 1118 and 1097 cm<sup>-1</sup> [C–O stretching] and 722 cm-1 [C–H bending (rocking)]. A peak around 1653 cm<sup>-1</sup> is attributed to C=C stretching (cis). The spectral region (1300-1000 cm<sup>-1</sup>) which contains FTIR fingerprints of the used oils was found to be very useful in detecting extra virgin olive oil adulteration. A band shift at 3005 cm<sup>-1</sup>; assigned to C–H stretching vibration of cis- double bond (=C–H) characteristic to extra virgin olive oil, was observed at higher wavenumbers with increasing adulterant concentration which allowed the determination of adulteration of extra virgin olive oil. The absorption intensity values of the spectral bands at 1163 cm<sup>-1</sup> (assigned to C–O stretching vibration and CH2 bending vibration) increased with increasing adulterant concentration. There was a pronounced shift of the peak at 912 cm<sup>-1</sup> (assigned to –HC=CH– of cis- double bond, bending out-of-plane) for extra virgin olive oil to higher wave numbers with increasing adulterant concentration. Absorbance ratios (R1118/1097 and R1747/2925 cm<sup>-1</sup>) decreased with increasing the concentrations of added adulterant oils (sunflower, corn and refined olive oils) with a fairly good linear relationship. The spectral region selected between 1800-900 cm<sup>-1</sup> mostly represented the combination of C–H bending, C=O stretching and C=C stretching and hence it was directly related to the unsaturated C=C bond. It played a very important role in the discriminant analysis. In conclusion, FTIR spectroscopy proved its potency to detect extra virgin olive oil adulteration at 5% level of adulterant oils (sunflower, corn and refined olive oils) which is much lower than the limit at which there exists a threatening of adulteration of extra virgin olive oil.