Recent Advances in Raman Analysis of Plants: Alkaloids, Carotenoids, and Polyacetylenes

This paper demonstrates the special potential of Raman spectroscopy for the study of selected plant metabolites. Carotenoids, which are beneficial components in fruits and vegetables, have been shown to be a significant factor in lowering the risk of various types of cancer and ischemic heart diseases. On the other hand, alkaloids may have various effects on human health, e.g. caffeine is a mild stimulant of the central nervous system and as a result it can influence human behaviour. Polyacetylenes are highly cytotoxic against numerous cancer cell lines and demonstrate antifungal, anti-inflammatory and anti-platelet-aggregatory properties. In most cases, vibrational measurements can be performed directly on plant tissues as well as on fractions isolated from the plant material by hydro-distillation or solvent extraction. Raman spectroscopy techniques allow obtaining spectra which present some characteristic key bands of individual components. Based on such markers related to individual plant substances, spectroscopic analyses in principle allow the discrimination of different species, and even chemotypes among the same species. Moreover, Raman microspectroscopy provides 2- and 3-dimensional images of the investigated plant samples. These maps can be directly compared to the corresponding visual images obtained from a light microscope and offer additional detailed information regarding the local distribution of specific compounds in the surface layers of the analyzed plant tissue.