269
9 Qualitative and Quantitative FT-Raman Analysis of Plants
ary phloem β-carotene increased gradually from periderm towards the core, but
declined fast in cells close to the vascular cambium. On the other hand, α-carotene
and lutein were deposited in younger cells with a higher rate than β-carotene, while
lycopene in red carrots accumulated throughout the whole secondary phloem at the
same level [93].
Reliable Ft-Raman methods were developed for the rapid determination of lycopene and other carotenoids occurring in tomatoes and various related products
such as tomato puree or tomato ketchup [94]. Compared to the spectrum of pure
isolated lycopene, the most intense C = C stretching vibration of this substance was
found to be slightly different in the Raman spectra obtained from the plant samples.
the authors assume that this shift is mainly caused by the interaction between the
naturally occurring carotenoids and the plant matrix changing their chemical form
or physical structure.
using an Ft-Raman spectrometer equipped with a microscope (40-fold amplification) carotenoid crystals sequestered in a carrot cell have been also measured
at the subcellular level [95]. the characteristic bands occurring at 1,518 cm
−1
and
1,156 cm
−1
proved that the crystals were predominantly formed from β-carotene.
Applying nonlinear coherent anti-Stokes Raman scattering (CARS) microscopy measurements of carotenoids in various thermally treated plant tissues such as
sweet potato, carrot, and mango were performed [96]. Based on the obtained CARS
signals, a quantification of size, shape, density, and location of different carotenoid
bodies could be achieved. In this context heterogeneous rod-shaped bodies with
high carotenoid densities were found for potatoes and carrots, whereas the carotenoid containing lipid droplets inside the mango fruits presented a more homogeneous low-density and rounded shape. After thermal treatment of the potatoes,
β-carotene density and morphology remained intact despite of significant changes
of the surrounding starch granules [96].
A range of naturally occurring carotenoids in numerous plant species have been
analysed using Ft-Raman spectroscopy [97]. here the authors stress that there may
be a significant wavenumber shift caused by carotenoid interactions with the surrounding plant tissue. the special potential of Raman spectroscopy was also applied
to characterize the different ripening stages of olives [98]. the authors showed that
the increase of triglycerides, carotenoids and phenolic compounds during the first
development stages and their decrease during the ripening process can be successfully monitored by means of the Raman bands at 1,525 and 1,605 cm
−1
, respectively.
Raman spectroscopy has been also applied to discriminate pollen grains of different tree species [99–101]. In this context single pollen Raman spectra are presented showing the individual key bands of carotenoids, proteins, nucleic acids,
carbohydrates, and lipids [99]. the classification of the different pollen species was
based on PCA as well as hierarchical cluster analyses (hCA) and allowed to analyze
various chemical classes of molecules simultaneously [100]. A similar study aiming
to measure the individual carotenoid profiles of different pollen grains of trees was
performed using the strong pre-resonant Raman spectra obtained before and after
photodepletion of the carotenoid molecules [101]. Without any further sample pre-
9 Qualitative and Quantitative FT-Raman Analysis of Plants
ary phloem β-carotene increased gradually from periderm towards the core, but
declined fast in cells close to the vascular cambium. On the other hand, α-carotene
and lutein were deposited in younger cells with a higher rate than β-carotene, while
lycopene in red carrots accumulated throughout the whole secondary phloem at the
same level [93].
Reliable Ft-Raman methods were developed for the rapid determination of lycopene and other carotenoids occurring in tomatoes and various related products
such as tomato puree or tomato ketchup [94]. Compared to the spectrum of pure
isolated lycopene, the most intense C = C stretching vibration of this substance was
found to be slightly different in the Raman spectra obtained from the plant samples.
the authors assume that this shift is mainly caused by the interaction between the
naturally occurring carotenoids and the plant matrix changing their chemical form
or physical structure.
using an Ft-Raman spectrometer equipped with a microscope (40-fold amplification) carotenoid crystals sequestered in a carrot cell have been also measured
at the subcellular level [95]. the characteristic bands occurring at 1,518 cm
−1
and
1,156 cm
−1
proved that the crystals were predominantly formed from β-carotene.
Applying nonlinear coherent anti-Stokes Raman scattering (CARS) microscopy measurements of carotenoids in various thermally treated plant tissues such as
sweet potato, carrot, and mango were performed [96]. Based on the obtained CARS
signals, a quantification of size, shape, density, and location of different carotenoid
bodies could be achieved. In this context heterogeneous rod-shaped bodies with
high carotenoid densities were found for potatoes and carrots, whereas the carotenoid containing lipid droplets inside the mango fruits presented a more homogeneous low-density and rounded shape. After thermal treatment of the potatoes,
β-carotene density and morphology remained intact despite of significant changes
of the surrounding starch granules [96].
A range of naturally occurring carotenoids in numerous plant species have been
analysed using Ft-Raman spectroscopy [97]. here the authors stress that there may
be a significant wavenumber shift caused by carotenoid interactions with the surrounding plant tissue. the special potential of Raman spectroscopy was also applied
to characterize the different ripening stages of olives [98]. the authors showed that
the increase of triglycerides, carotenoids and phenolic compounds during the first
development stages and their decrease during the ripening process can be successfully monitored by means of the Raman bands at 1,525 and 1,605 cm
−1
, respectively.
Raman spectroscopy has been also applied to discriminate pollen grains of different tree species [99–101]. In this context single pollen Raman spectra are presented showing the individual key bands of carotenoids, proteins, nucleic acids,
carbohydrates, and lipids [99]. the classification of the different pollen species was
based on PCA as well as hierarchical cluster analyses (hCA) and allowed to analyze
various chemical classes of molecules simultaneously [100]. A similar study aiming
to measure the individual carotenoid profiles of different pollen grains of trees was
performed using the strong pre-resonant Raman spectra obtained before and after
photodepletion of the carotenoid molecules [101]. Without any further sample pre-