Multivariate analysis of uronic acid and neutral sugars in whole pectic samples by FT-IR spectroscopy

The sequential extraction of the cell wall material (CWM) of olive and orange pulps and its subsequent fractionation by ethanol precipitation and anion-exchange chromatography gave a wide range of cell wall polysaccharide fractions. The fractions rich in pectic polysaccharides, characterised by the presence of uronic acid, rhamnose, arabinose and galactose monosaccharides released by acid hydrolysis, were selected, 13 from olive and 11 from orange. The FT-IR spectrum of a pectic polysaccharide sample shows characteristic absorbances in the region between 1200 and 850 cm(-1); samples rich in uronic acid show two intense peaks at 1110 and 1018 cm(-1). Although the peaks are readily observable, simple quantification is difficult because of the underlying spectral structure. To verify if this region is useful for the characterisation of the pectic polysaccharides, a multivariate analysis was performed. This region allows prediction of the uronic acid and neutral sugars' pectic side chains of the two distinct fruits. In order to highlight the selective wavenumbers for the determination of the sugar components of the pectic polysaccharides from olive and orange, it was performed on a selection of variables based on a mathematical method that uses the signal to noise ratio. This study showed that the FT-IR spectra have the potential to be an important source of information for a quick evaluation of the polysaccharide composition of samples of pectic origin. (C) 1998 Elsevier Science Ltd. All rights reserved.