Biospectroscopy of Rhododendron indicum flowers. Non-destructive assessment of anthocyanins in petals using a reflectance-based method

Abstract

Reflectance spectra from pink petals of Rhododendron indicum flowers showed absorption in the NIR (1470, 1930 and 2500 nm) due to water, in the visible (533 nm, due to anthocyanins) and in the UV (broad absorption due to phenolic compounds other than anthocyanins). A linear correlation between the remission function at 533 nm and the anthocyanin content in μmol per g fresh weight has been found, allowing non-destructive quantification of anthocyanins. The remission function could be obtained either from reflectance of a group of stacked petals (Kubelka–Munk theory) or through determination of the absorption and scattering coefficients following the Pile of Plates model. The intact petals have shown fluorescence emission in the blue (400–500 nm) and in the visible around 624 nm under UV excitation. The red emission was attributed to anthocyanins whereas blue emission was assigned to other phenolic compounds. On the basis of absorption and fluorescence measurements of crude and purified extracts from the petals, the last compounds could possibly be a mixture of flavonoids and hydroxycinnamic-type plant phenolics such as ferulic acid, chlorogenic acid or others.