Structural Changes of Polyacetylenes in American Ginseng Root Can Be Observed in Situ by Using Raman Spectroscopy

The presented results show the special advantage of Raman spectroscopy in the investigation of polyacetylenes in American ginseng (Panax quinquefolium L.) roots. The compounds are measured directly in the plant tissue without any preliminary sample preparation. The polyacetylene signal is strong and well-separated from other bands so the spectral impact of the surrounding biological matrix can be clearly distinguished. The Raman spectrum taken in situ from the fresh ginseng root revealed a characteristic polyacetylene key band at 2237 cm-1 whereas in the spectrum obtained from dried root this band was shifted to about 2258 cm-1. The latter is in good agreement with signals obtained from isolated standards, falcarinol (2258 cm-1) and panaxydol (2260 cm-1), occurring as predominant polyacetylenes in this species. The shift of the polyacetylene band observed in root extracts or at a certain stage of root drying indicates the molecular modification of polyacetylenes resulting from the loss of water. Furthermore, it was found that the process upon root hydration is reversible as the shift of polyacetylene band from 2258 to 2237 cm-1 is observed. An explanation of this phenomenon can be an interaction of polyacetylene molecules with plant components in the presence of water molecules forming a stable entity in situ that is broken after dehydration (loss of water) of the fresh ginseng root. Application of the Raman mapping technique to ginseng roots of different size showed that the content of both main polyacetylenes decreases with increasing root size in accordance with quantitative high-performance liquid chromatography data. Keywords: Panax quinquefolium; FT-Raman; mapping; falcarinol; panaxydol; nondestructive analysis; in situ