Study of phenolic extractability in grape seeds by means of ATR-FTIR and Raman spectroscopy

- Grape seeds have been analysed using mid infrared absorption and Raman spectroscopy.
- Phenolic compounds extractabilities were determined for grape seed samples.
- Grape variety and phenolic compound extractability were observed to be correlated.
- Spectral features confirmed phenolic extraction is linked to cell wall composition.

Near infrared hyperspectral imaging has been applied to grape seeds in order to select a representative subset of samples according to their spectral features in the 900-1700 nm range. Afterwards, selected grape seeds have been classified according to their total phenol and flavanol extractabilities. In this way, samples were sorted in three different groups identified as low, medium and high extractability levels.In order to establish the chemical structures which can be responsible for the different extractabilities, vibrational spectroscopy has been applied to the non-extracted material after seed extractions. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) and Raman spectra of non-extracted seed material have been recorded and their main spectral features have been linked to extractabilities of flavanolic and total phenolic compounds.The vibrational spectroscopic analysis confirms that grape seed phenolic extractability is influenced by the cell wall composition (polysaccharides, lignins, pectins) and by the degree of esterification of pectins.

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