255
9 Qualitative and Quantitative FT-Raman Analysis of Plants
9.2 Primary Substances
Primary substances of plant origin (carbohydrates, amino acids, fats, oils and proteins) occur in all cells and are responsible for the individual biochemical processes
necessary to produce enough energy, to maintain life, or to stimulate growth of the
respective organism. Furthermore, from these basic substances numerous secondary metabolites, exhibiting various healthy properties for human beings, are biosynthesized.
9.2.1 Fatty Oils and Waxes
vegetable oils obtained from various oil plants such as, coconut, corn, high oleic
sunflower, olive oil, peanut, Brazil nut, palm, palm kernel, rapeseed, soybean by
mechanical or solvent extraction show characteristic Raman bands in the region of
1,440–1,660 cm
−1
which are related to C = C stretching modes of cis-unsaturated
fatty acids as well as Ch 2 -scissoring modes of saturated fatty acids [9]. In addition
characteristic signals occur in the region between 2,990 and 3,020 cm
−1
. the Raman
shifts around 3,010 cm
−1
were assigned as ν ( = C-h) modes of the olefinic triglycerides
which can be used as a reliable indicator of the different degrees of unsaturation
[9, 10]. Furthermore, these signals can also be used to accurately predict the individual iodine value of vegetable oils as well as to detect and quantify adulterations
in olive oil. other scattering Raman shifts registered at 1,663 and 1,264 cm
−1
were
also found to correlate with the individual fatty acid profiles determined by gas
chromatography.
vegetable oils present a comparatively weak carbonyl Raman band around
1,750 cm
−1
. other signals can be observed in the range between 1,650 and 1,670 cm
−1
which are assigned to ν (C = C) vibrations of the unsaturated triglycerides. the fingerprint region between 700 and 1,200 cm
−1
shows the characteristic C-C skeletal and
C-o bond vibrations and provides mainly information about the unsaturated fatty
acids [9]. Several Raman studies have been performed to determine oil content,
humidity and free fatty acid content in olives [11, 12] or to quantify the amount of
sunflower oil adulterant in extra-virgin olive oil from various mediterranean sites
[13]. A new method has been also developed to rapidly predict the iodine value in
single rapeseeds [14]. this approach is very useful for breeding research and applied breeding to measure the lipid content and composition of a seedling without
to destroy the plant tissue. thus, the authors were able to distinguish seedlings of a
classic rapeseed cultivar from a new genetically modified cultivar. this successful
discrimination by means of cluster analysis based on Raman data is mainly related
to a lower iodine value of the genetically modified cultivar, as it contains myristic
acid which is normally not detectable in the fatty acid profile of rape.
Several studies have been performed applying Raman spectroscopy to discriminate between different edible oils and fats [15–17]. using linear discriminant
analysis (LdA) and canonical variate analysis (CvA) adulterants of edible oils
9 Qualitative and Quantitative FT-Raman Analysis of Plants
9.2 Primary Substances
Primary substances of plant origin (carbohydrates, amino acids, fats, oils and proteins) occur in all cells and are responsible for the individual biochemical processes
necessary to produce enough energy, to maintain life, or to stimulate growth of the
respective organism. Furthermore, from these basic substances numerous secondary metabolites, exhibiting various healthy properties for human beings, are biosynthesized.
9.2.1 Fatty Oils and Waxes
vegetable oils obtained from various oil plants such as, coconut, corn, high oleic
sunflower, olive oil, peanut, Brazil nut, palm, palm kernel, rapeseed, soybean by
mechanical or solvent extraction show characteristic Raman bands in the region of
1,440–1,660 cm
−1
which are related to C = C stretching modes of cis-unsaturated
fatty acids as well as Ch 2 -scissoring modes of saturated fatty acids [9]. In addition
characteristic signals occur in the region between 2,990 and 3,020 cm
−1
. the Raman
shifts around 3,010 cm
−1
were assigned as ν ( = C-h) modes of the olefinic triglycerides
which can be used as a reliable indicator of the different degrees of unsaturation
[9, 10]. Furthermore, these signals can also be used to accurately predict the individual iodine value of vegetable oils as well as to detect and quantify adulterations
in olive oil. other scattering Raman shifts registered at 1,663 and 1,264 cm
−1
were
also found to correlate with the individual fatty acid profiles determined by gas
chromatography.
vegetable oils present a comparatively weak carbonyl Raman band around
1,750 cm
−1
. other signals can be observed in the range between 1,650 and 1,670 cm
−1
which are assigned to ν (C = C) vibrations of the unsaturated triglycerides. the fingerprint region between 700 and 1,200 cm
−1
shows the characteristic C-C skeletal and
C-o bond vibrations and provides mainly information about the unsaturated fatty
acids [9]. Several Raman studies have been performed to determine oil content,
humidity and free fatty acid content in olives [11, 12] or to quantify the amount of
sunflower oil adulterant in extra-virgin olive oil from various mediterranean sites
[13]. A new method has been also developed to rapidly predict the iodine value in
single rapeseeds [14]. this approach is very useful for breeding research and applied breeding to measure the lipid content and composition of a seedling without
to destroy the plant tissue. thus, the authors were able to distinguish seedlings of a
classic rapeseed cultivar from a new genetically modified cultivar. this successful
discrimination by means of cluster analysis based on Raman data is mainly related
to a lower iodine value of the genetically modified cultivar, as it contains myristic
acid which is normally not detectable in the fatty acid profile of rape.
Several studies have been performed applying Raman spectroscopy to discriminate between different edible oils and fats [15–17]. using linear discriminant
analysis (LdA) and canonical variate analysis (CvA) adulterants of edible oils