Characterization and discrimination of phenolic compounds using Fourier transform Raman spectroscopy and chemometric tools

Abstract

Description of the subject. Phenolic compounds (PCs) are the most abundant secondary metabolites in plants. This work was part of a study that sought to develop rapid screening FT-Raman methods for identifying and quantifying classes and/or types of PCs in the dry extracts of plant products. Objectives. Fourier transform Raman spectroscopy (FT-Raman) coupled with chemometric tools was used to characterize and discriminate four families of phenolic compounds: two important classes of phenolic acids, hydroxybenzoic and hydroxycinnamic acids, as well as their derivatives and flavonoids. Method. For this study, 25 standards of phenolic compounds were used (47 standards in total, taking account of the different brands). Repeatability and reproducibility studies were conducted to verify the Raman assignments of gallic acid. Raman characterization with the most significant spectral bands of phenolic compounds was done using spectra ranging from 1,800 to 50 cm -1 . A Fisher test was applied to pre-processed Raman spectra (SNV) and 20 Raman scattering signals were used to differentiate each class of phenolic compounds. Results. Hydroxybenzoic acids, hydroxycinnamic acids, their derivatives and flavonoids have been characterized by Raman spectroscopy; bands have been identified and differentiated within and between groups. Conclusions. The scattering intensities located around 1,600-1,699, 1,300-1,400 and below 200 cm -1 were responsible for differentiating 100% of phenolic compound families, classes and subclasses.

Potential of Spatially Offset Raman Spectroscopy for Detection of Zebra Chip and Potato Virus Y Diseases of Potatoes (Solanum tuberosum)

“…Vibrational band assignments were made on the basis of previously reported spectroscopic analyses of carbohydrates, protein, carotenoids, and polyphenols (Table ). − We believe that most of these bands are likely associated with carbohydrates. To confirm this, we obtained the Raman spectra of powdered pectin and amylopectin (Figure S2)…”

Rapid and Noninvasive Typing and Assessment of Nutrient Content of Maize Kernels Using a Handheld Raman Spectrometer

“…Fibers are polyphenolic molecular assemblies that have two distinct vibrational bands in Raman spectra. , The band at 1600 cm –1 can be assigned to C–C ring stretching and symmetric C–H vibration . The 1632 cm –1 band originates from CC aromatic ring vibration . ANOVA revealed at least two groups of maize based on the fiber content.…”

Vibrational Study (Raman, SERS, and IR) of Plant Gallnut Polyphenols Related to the Fabrication of Iron Gall Inks

“…Performing a complete and detailed vibrational assignment is not a simple task. In fact, no satisfactory assignment of the bands was found in the literature, although the Raman spectra of many phenolic compounds have been already published [ 38 , 46 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. Furthermore, the comparison of the IR and Raman spectra also serves as an additional assistance toward a more accurate assignment, since they are complementary due to the different selection rules applied in these techniques, which give rise to vibrational bands with different relative intensities.…”

“…The characterization of IGIs by Raman spectroscopy requires a previous analysis of the polyphenols integrated in gallnuts. Although this kind of study has been performed for different phenolic compounds [ 38 , 39 ], a comprehensive comparative analysis is necessary to distinguish between the main vibrational features in a mixture of such gallnut compounds. Raman spectroscopy alone is not always able to distinguish the sources of specific functional groups, especially in such complex systems as (paper-based) artifacts.…”