267
9 Qualitative and Quantitative FT-Raman Analysis of Plants
seen. Furthermore, several sabinene bands of minor intensity occur in the range
between 600 and 1,000 cm
−1
(δ C-C at 950 cm
−1
and ring deformation vibration at
652 cm
−1
). The Raman spectrum of the “δ-3-carene/caryophyllene/limonene type”,
shows signals of all three main components, δ-3-carene (key bands at 1,686, 819,
713 and 678 cm
−1
), caryophyllene (key band at 1,632 and 1,671 cm
−1
) and limonene
(key band at 760 cm
−1
).
Raman spectroscopy was also successfully applied for chemotype discrimination of marjoram and oregano essential oils as well as for identification of the essential oil constituents [81]. the essential oils isolated from various basil species
and cultivars have been also analysed by means of Raman spectroscopy and 11
chemotypes could be successfully classified [82].
Raman spectra obtained from various citrus oils (orange, grapefruit, mandarin,
lemon, and lime) [72] show more or less a similar spectral profile. Some of the
most relevant monoterpene components occurring in the oil, such as limonene and
γ-terpinene, show characteristic key bands, which are useful for a quantitative distinction of the different oil types. Applying principal component analysis (PCA) to
the spectral data, the individual citrus oils can be clearly separated in a 3-dimensional factor space. Cross-validation statistics showed that a partial least square
(PLS) algorithm was able to produce high quality predictions of the relative oil
composition as well as general quality parameters. the dominating bands are due
to limonene vibrations and are recorded at 760, 1,435, 1,644/1,678 cm
−1
. Based on
the first three PCA factors, 86 % of the total variation could be explained. Applying
the PLS algorithm all relevant oil components as well as sum parameters (total aldehyde content, optical rotation) of the various citrus oils were precisely analyzed.
Calibration curves for the prediction of α-pinene and β-myrcene occurring in
mastic gum oil have been developed [74]. the authors report, that the correlation
coefficient was calculated to be 0.992 and 0.997, respectively.
Recently, a novel approach was reported to analyse in situ (-)-bornyl acetate in
the essential oil of Sibirian fir ( Abies sibirica) by means of Raman optical activity (RoA) [83]. Characteristic Raman signals were observed at 1,688, 1,659 and
1,639 cm
−1
due to C = C stretching vibrations originating from the four main components (bornyl acetate, camphene, α-pinene, 3-carene) of the essential oil. The
experimental results correlated very well with simulated RoA and Raman spectra
of bornyl acetate obtained from dFt calculations. the authors mention that this
method has the potential to become a standard procedure for commercial essential
oil analysis.
9.3.4 Carotenoids
Carotenoids occur in chromoplasts of plants and algae and are responsible for their
characteristic yellow, orange or red-color. generally, plant pigments such as carotenoids, anthocanins and flavonoids fulfill the task to attract insects and birds for
the purpose of pollination and thus to guarantee the preservation of the individual
9 Qualitative and Quantitative FT-Raman Analysis of Plants
seen. Furthermore, several sabinene bands of minor intensity occur in the range
between 600 and 1,000 cm
−1
(δ C-C at 950 cm
−1
and ring deformation vibration at
652 cm
−1
). The Raman spectrum of the “δ-3-carene/caryophyllene/limonene type”,
shows signals of all three main components, δ-3-carene (key bands at 1,686, 819,
713 and 678 cm
−1
), caryophyllene (key band at 1,632 and 1,671 cm
−1
) and limonene
(key band at 760 cm
−1
).
Raman spectroscopy was also successfully applied for chemotype discrimination of marjoram and oregano essential oils as well as for identification of the essential oil constituents [81]. the essential oils isolated from various basil species
and cultivars have been also analysed by means of Raman spectroscopy and 11
chemotypes could be successfully classified [82].
Raman spectra obtained from various citrus oils (orange, grapefruit, mandarin,
lemon, and lime) [72] show more or less a similar spectral profile. Some of the
most relevant monoterpene components occurring in the oil, such as limonene and
γ-terpinene, show characteristic key bands, which are useful for a quantitative distinction of the different oil types. Applying principal component analysis (PCA) to
the spectral data, the individual citrus oils can be clearly separated in a 3-dimensional factor space. Cross-validation statistics showed that a partial least square
(PLS) algorithm was able to produce high quality predictions of the relative oil
composition as well as general quality parameters. the dominating bands are due
to limonene vibrations and are recorded at 760, 1,435, 1,644/1,678 cm
−1
. Based on
the first three PCA factors, 86 % of the total variation could be explained. Applying
the PLS algorithm all relevant oil components as well as sum parameters (total aldehyde content, optical rotation) of the various citrus oils were precisely analyzed.
Calibration curves for the prediction of α-pinene and β-myrcene occurring in
mastic gum oil have been developed [74]. the authors report, that the correlation
coefficient was calculated to be 0.992 and 0.997, respectively.
Recently, a novel approach was reported to analyse in situ (-)-bornyl acetate in
the essential oil of Sibirian fir ( Abies sibirica) by means of Raman optical activity (RoA) [83]. Characteristic Raman signals were observed at 1,688, 1,659 and
1,639 cm
−1
due to C = C stretching vibrations originating from the four main components (bornyl acetate, camphene, α-pinene, 3-carene) of the essential oil. The
experimental results correlated very well with simulated RoA and Raman spectra
of bornyl acetate obtained from dFt calculations. the authors mention that this
method has the potential to become a standard procedure for commercial essential
oil analysis.
9.3.4 Carotenoids
Carotenoids occur in chromoplasts of plants and algae and are responsible for their
characteristic yellow, orange or red-color. generally, plant pigments such as carotenoids, anthocanins and flavonoids fulfill the task to attract insects and birds for
the purpose of pollination and thus to guarantee the preservation of the individual