• Raman spectroscopy;
  • carotenoids;
  • plant tissue;
  • polyene conjugation


Raman spectroscopic studies of a range of naturally occurring carotenoids in over 50 specimens of plant tissue and a range of standard extracts have been undertaken, and the characteristic bands of C[DOUBLE BOND]C and C[BOND]C stretching and C[BOND]CH bending have been recorded. Comparison of the spectroscopic data with the chemical assignment of the carotenoids from chemical extraction of the plant tissues reveals that there is a problem in the interpretation of the spectroscopic data which can be attributed to significant wavenumber shifts, particularly in the C[DOUBLE BOND]C stretching band wavenumber, for carotenoids in the organic tissues arising from molecular interactions between the carotenoid and its host matrix. The simple identification of carotenoids in biological tissues on the basis of comparison with the standard spectra of extracted material must be made with caution; the progressive shift in wavenumber of the C[DOUBLE BOND]C stretching band in the conjugated polyene chain of carotenoids with the number of C[DOUBLE BOND]C groups, and hence the identification of the carotenoid, cannot be unambiguously interpreted for the range of materials studied here. Copyright © 2009 John Wiley & Sons, Ltd.