The contents of bibenzyl derivatives, flavonoids and a phenanthrene in selected Dendrobium spp. and the correlation with their antioxidant activity

Dendrobium spp. (the Orchidaceae family) is widely distributed in Asian countries. The fresh or dried stems of Dendrobium spp. have long been used in traditional Chinese medicine for their tonic and antipyretic properties. Bibenzyl derivatives (moscatilin, gigantol, crepidatin, and chrysotoxin), flavonoids (eriodictyol and homoeriodictyol) and phenanthrene lusianthridin are the major active compounds in the stems of Dendrobium spp. Most of these compounds have been recorded in these plants in Thailand; however, their concentrations have not yet been reported. Therefore, in this study, dried stems of selected Dendrobium spp. (33 species) in Thailand were extracted and analyzed by using high-performance liquid chromatography (HPLC). The HPLC method was performed on a reversed-phase column using a mobile phase gradient system of 20-32% acetonitrile in 1.5% acetic acid with a flow rate of 0.8 ml/min and a detection wavelength of 280 nm. The HPLC method displayed good linearity with coefficients of determination (R-2 > 0.997) for the seven active compounds analyzed. The variation in intra- and inter-day analysis (%RSD) was less than 0.5%. Additionally, the extracts of selected Dendrobium spp. were investigated for antioxidant activity by DPPH and FRAP radical scavenging assays. The results showed good activities in some species. The correlation between the seven active compounds and the antioxidant levels (IC50 and FRAP values) were significant in bibenzyl derivatives and homoeriodictyol as determined by the Pearson correlation. In conclusion, the developed HPLC method can be used for the determination of active compounds in Dendrobium spp., which is useful for further studies of the species containing the highest levels of these compounds.