256
H. Schulz
and the individual botanical origin were identified. A similar approach has been
presented by Weng et al. [18] to prove the authenticity of Camelia oleifera oil used
in taiwan.
A rapid method to detect adulterations of extra virgin olive oil with cheaper vegetable oils has been also described [19]. Based on various extra virgin oil samples
exhibiting different amounts of olive oil adulteration, a suitable calibration equation
was developed (R
2
= 0.997, SEP = 1.72 %) allowing to detect even low amounts of
other added vegetable oils. the potential capability of Raman spectroscopy to identify and quantify monoterpenes isolated from aromatic plants in olive oil was studied by omar et al. [20]. they mixed olive oil with different amounts of rosemary oil,
measured in the range between 150 and 3,000 cm
−1
and developed calibrations for
eucalyptol and camphor. the predicted concentrations of essential oil in the analysed olive oil samples were found to correlate very well with the reference gC data.
the authors stress that Raman spectroscopy is therefore a useful screening method
for various purposes in the field of food chemistry.
Another approach for discrimination of olive oils from various cheaper vegetable oils (sunflower oil, safflower oil, soybean oil, wheat germ oil, walnut oil,
flaxseed oil) has been developed by El-Abassy and al. [21]. Raman measurements
were carried out using excitation at 514.5 nm. For signal detection, a CCd detector
was employed recording the complete spectral range of interest between 700 and
3,100 cm
−1
. Adulterations with sunflower oil, rapeseed oil and soybean oil could be
easily detected, because the characteristic carotenoid bands to be seen in the spectrum of olive oil at 1,008, 150 and 1,525 cm
−1
decrease significantly when these
edible oils are added. the amount of sunflower oil in adulterated extra-virgin olive
oil could be determined by applying the PLS regression algorithm. In this context a
lower detection limit of approx. 500 mg/kg adulterated oil was determined.
usually, the amount of trans-isomers in partially hydrogenated vegetable oils
is detected by gC or mid-infrared spectroscopy but Raman spectroscopy was also
evaluated in comparison to mid IR spectroscopy to predict the content of cis- and
trans-isomers in processed canola and soybean oils [22, 23].
the studies of [24] show that Raman microscopy is useful to discriminate even
between different tocopherols and their oxidation products such as α-tocopheryl
quinine. Parker and Bisby [1] presented time-resolved resonance Raman spectra
of the α-tocopheroxyl radical which represents an intermediate in the antioxidative
reaction of α-tocopherol in cellular membranes. The spectra reflect the extent of
delocalisation of the radical site due to interaction with the ion pair of the paraoxygen atom.
the epicuticular wax of mature mango fruits ( Mangifera indica) were successfully characterised by means of Raman spectroscopy [25]. Raman measurements
presented two morphologically different parts in the wax layer, a crystalline outermost layer and a smooth layer next to the cuticula. Furthermore, the Raman studies
were useful to clarify problems faced by the mango industry related to discoloration
around lenticels.
H. Schulz
and the individual botanical origin were identified. A similar approach has been
presented by Weng et al. [18] to prove the authenticity of Camelia oleifera oil used
in taiwan.
A rapid method to detect adulterations of extra virgin olive oil with cheaper vegetable oils has been also described [19]. Based on various extra virgin oil samples
exhibiting different amounts of olive oil adulteration, a suitable calibration equation
was developed (R
2
= 0.997, SEP = 1.72 %) allowing to detect even low amounts of
other added vegetable oils. the potential capability of Raman spectroscopy to identify and quantify monoterpenes isolated from aromatic plants in olive oil was studied by omar et al. [20]. they mixed olive oil with different amounts of rosemary oil,
measured in the range between 150 and 3,000 cm
−1
and developed calibrations for
eucalyptol and camphor. the predicted concentrations of essential oil in the analysed olive oil samples were found to correlate very well with the reference gC data.
the authors stress that Raman spectroscopy is therefore a useful screening method
for various purposes in the field of food chemistry.
Another approach for discrimination of olive oils from various cheaper vegetable oils (sunflower oil, safflower oil, soybean oil, wheat germ oil, walnut oil,
flaxseed oil) has been developed by El-Abassy and al. [21]. Raman measurements
were carried out using excitation at 514.5 nm. For signal detection, a CCd detector
was employed recording the complete spectral range of interest between 700 and
3,100 cm
−1
. Adulterations with sunflower oil, rapeseed oil and soybean oil could be
easily detected, because the characteristic carotenoid bands to be seen in the spectrum of olive oil at 1,008, 150 and 1,525 cm
−1
decrease significantly when these
edible oils are added. the amount of sunflower oil in adulterated extra-virgin olive
oil could be determined by applying the PLS regression algorithm. In this context a
lower detection limit of approx. 500 mg/kg adulterated oil was determined.
usually, the amount of trans-isomers in partially hydrogenated vegetable oils
is detected by gC or mid-infrared spectroscopy but Raman spectroscopy was also
evaluated in comparison to mid IR spectroscopy to predict the content of cis- and
trans-isomers in processed canola and soybean oils [22, 23].
the studies of [24] show that Raman microscopy is useful to discriminate even
between different tocopherols and their oxidation products such as α-tocopheryl
quinine. Parker and Bisby [1] presented time-resolved resonance Raman spectra
of the α-tocopheroxyl radical which represents an intermediate in the antioxidative
reaction of α-tocopherol in cellular membranes. The spectra reflect the extent of
delocalisation of the radical site due to interaction with the ion pair of the paraoxygen atom.
the epicuticular wax of mature mango fruits ( Mangifera indica) were successfully characterised by means of Raman spectroscopy [25]. Raman measurements
presented two morphologically different parts in the wax layer, a crystalline outermost layer and a smooth layer next to the cuticula. Furthermore, the Raman studies
were useful to clarify problems faced by the mango industry related to discoloration
around lenticels.