268
H. Schulz
species [84]. the main role of carotenoids in plants is related to photosynthesis
where they interact between light absorption, excitation energy transfer, dissipation of excess energy and electron transfer processes. Carotenoids are located in
antenna-proteins forming light-harvesting complexes, which surround a photosynthetic center to focus photon energies absorbed by the pigment, and to transport the
excitation energy to the reaction center where it is converted into chemical energy
driving the photosynthetic reaction [85].
Raman spectra of β-carotene show three characteristic bands at 1,524, 1,157 and
1,005 cm
−1
, respectively, which are assigned as double bond C = C stretching mode
(1,524 cm
−1
), C-C in-plane single bond stretching mode (1,157 cm
−1
), and C-h
bending mode (1,008 cm
−1
), respectively.
Already in early 1970s the resonance Raman spectra for astaxanthin were measured and a correlation between the absorption spectra and the resonance Raman
excitation profiles of this carotinoid substance was found [86].
Recently, it has been observed that the position of C = C stretching vibrations
in the Raman spectrum is mainly influenced both by the carotenoid polyene chain
length and the structure of terminal substituents [87]. Based on this finding it is
principally possible analyzing simultaneously the distribution of different carotenoids in plant tissue [88]. Even unstable epoxycarotenoids such as auroxanthin and
violaxanthin were detected with high sensitivity and their distribution in the plant
tissue could be measured in situ applying micro-Raman mapping [53, 88]. Furthermore, Ft-Raman microspectroscopy has been used to demonstrate the microstructure and chemical composition of fennel fruits, chamomile inflorescence and curcuma roots [77]. Ft-Raman imaging or mapping of carotenoid distribution also seems
to be a suitable approach to show possible changes in the plant metabolism induced
by abiotic and biotic stresses as well as sunscald physiological disorder [89].
Changes of carotinoid distribution was also found in leaves of diseased sugarbeet ( Beta vulgaris L.) and in leaves of parsley ( Petroselinum crispum mill. Nym.)
which were infected by the fungus Septoria petroselini [89].
It is well known that during ripening the composition of the carotenoid fraction
cessfully applied e.g. to characterize the content of lutein, β-carotene and capsanthin in the individual ripening stages of bell pepper ( Capsicum annum) [89]. Quite
recently, confocal Raman has been used to identify in parallel lycopene, β-carotene,
and lutein in tomato fruits [90]. the authors mention that this technique provides
some advantages for the food industry in order to get a rapid information of fruit
quality during processing.
Comprehensive Raman studies of carrots ( Daucus carota) show that various
quality parameters such as carotenoids, polyacetylenes, pectin and starch can be
determined simultaneously in wild and cultivated roots [90, 92]. moreover, the distribution of α- and β-carotene as well as lutein and lycopene was analysed in root
sections of various carrot cultivars. this finding was possible due to the ability to
separate different Raman bands to β-carotene (1,520 cm
−1
), lycopene (1,510 cm
−1
)
and α-carotene/lutein (1,527 cm
−1
). Clearly, the level of β-carotene was heterogeneous across root sections of orange, yellow, red and purple roots. In the second-
H. Schulz
species [84]. the main role of carotenoids in plants is related to photosynthesis
where they interact between light absorption, excitation energy transfer, dissipation of excess energy and electron transfer processes. Carotenoids are located in
antenna-proteins forming light-harvesting complexes, which surround a photosynthetic center to focus photon energies absorbed by the pigment, and to transport the
excitation energy to the reaction center where it is converted into chemical energy
driving the photosynthetic reaction [85].
Raman spectra of β-carotene show three characteristic bands at 1,524, 1,157 and
1,005 cm
−1
, respectively, which are assigned as double bond C = C stretching mode
(1,524 cm
−1
), C-C in-plane single bond stretching mode (1,157 cm
−1
), and C-h
bending mode (1,008 cm
−1
), respectively.
Already in early 1970s the resonance Raman spectra for astaxanthin were measured and a correlation between the absorption spectra and the resonance Raman
excitation profiles of this carotinoid substance was found [86].
Recently, it has been observed that the position of C = C stretching vibrations
in the Raman spectrum is mainly influenced both by the carotenoid polyene chain
length and the structure of terminal substituents [87]. Based on this finding it is
principally possible analyzing simultaneously the distribution of different carotenoids in plant tissue [88]. Even unstable epoxycarotenoids such as auroxanthin and
violaxanthin were detected with high sensitivity and their distribution in the plant
tissue could be measured in situ applying micro-Raman mapping [53, 88]. Furthermore, Ft-Raman microspectroscopy has been used to demonstrate the microstructure and chemical composition of fennel fruits, chamomile inflorescence and curcuma roots [77]. Ft-Raman imaging or mapping of carotenoid distribution also seems
to be a suitable approach to show possible changes in the plant metabolism induced
by abiotic and biotic stresses as well as sunscald physiological disorder [89].
Changes of carotinoid distribution was also found in leaves of diseased sugarbeet ( Beta vulgaris L.) and in leaves of parsley ( Petroselinum crispum mill. Nym.)
which were infected by the fungus Septoria petroselini [89].
It is well known that during ripening the composition of the carotenoid fraction
cessfully applied e.g. to characterize the content of lutein, β-carotene and capsanthin in the individual ripening stages of bell pepper ( Capsicum annum) [89]. Quite
recently, confocal Raman has been used to identify in parallel lycopene, β-carotene,
and lutein in tomato fruits [90]. the authors mention that this technique provides
some advantages for the food industry in order to get a rapid information of fruit
quality during processing.
Comprehensive Raman studies of carrots ( Daucus carota) show that various
quality parameters such as carotenoids, polyacetylenes, pectin and starch can be
determined simultaneously in wild and cultivated roots [90, 92]. moreover, the distribution of α- and β-carotene as well as lutein and lycopene was analysed in root
sections of various carrot cultivars. this finding was possible due to the ability to
separate different Raman bands to β-carotene (1,520 cm
−1
), lycopene (1,510 cm
−1
)
and α-carotene/lutein (1,527 cm
−1
). Clearly, the level of β-carotene was heterogeneous across root sections of orange, yellow, red and purple roots. In the second-