In Situ Flavonoid Analysis by FT-Raman Spectroscopy:  Identification, Distribution, and Quantification of Aspalathin in Green Rooibos (Aspalathus linearis)

Abstract

FT-Raman spectroscopy was used for the first time for in situ identification of aspalathin and quantification of the dihyrochalcones in dried, green rooibos (Aspalathus linearis). With the support of two-dimensional correlation spectroscopy, characteristic key bands of aspalathin, the main flavonoid and antioxidant occurring in rooibos, were localized and identified in the spectra obtained from various plant samples. Application of Raman mapping revealed the spatial distribution of this valuable dihydrochalcone within the intact dried leaves. Based on the spectral data and reference HPLC values, reliable multivariate calibration models were developed for quantification of aspalathin, nothofagin, and the combined dihydrochalcone contents of dried, green rooibos.

SERS of plant material

“…If this were the case, we would expect to see significant contributions of the antioxidants to the Raman spectra, due to their proximity to the metal colloids. Our measured spectra for some typical antioxidant materials (specifically flavanoids) as well as Raman 37 and SERS 38 measurements differ from those obtained here for the whole plants. However, a partial contribution of the flavanoids together with that of other biochemicals cannot be ruled out.…”

Chemometric Analysis of Raman and IR Spectra of Natural Dyes

“…What is interesting, authors detected malvidin 3-glucoside in "Pinot noir" berries both in the quinonoidal base form (strong band at 1653 cm −1 ) and in the flavylium form (features at 1,572, 1,600 and 1,648 cm −1 ). the Raman mapping has been shown for green rooibos ( Aspalathus linearis) where the aspalanthin, a dihydrochalcone, is the major flavonoid component [66]. From these results it can be seen that the aspalanthin is distributed heterogeneously in the sample and the highest concentration was observed in the inner part of the leaves.…”

“…the PLS method applied in RS is so-called "full spectrum method" what means that calibration model is improved with an increasing number of data points, in opposite to methods which require to choose the marker bands [66].…”

“…Nevertheless, the in situ quantitative analysis is possible. the quantification of aspalathin and nothofagin in green rooibos ( Aspalathus linearis) was performed with Ft-Raman spectroscopy together with flavonoid mapping in plant mentioned above [66]. the Ft-Raman calibration for aspalathin model resulted in R 2 = 0.87 (SECv = 0.53 g/100 g) whilst for nothofagin showed R 2 = 0.78 (SECv-0.14 g/100 g).…”

FT-Raman spectroscopy as a tool in evaluation the response of plants to drought stress

“…The content of pigments in the leaf samples collected before and after the drought was measured using one of the most popular methods, i.e., the spectrophotometric method described by Lichtenthaler and Wellburn [19], which as all classical analytical method, is time-consuming, laborious and requires the intake of reagents. Raman spectroscopy with Fourier transformation (FT-Raman) can serve as an alternative, non-invasive technique useful for the characterization and identification of the pigment content (especially carotenoids) in living tissue [21][22][23][24][25]. Our study has applied FT-Raman spectroscopy for the first time in the analysis of the effect of drought stress on the chemical composition of plant tissue, including the content of carotenoids and chlorophylls.…”