Comparative vibrational spectroscopy for determination of quality parameters in amidated pectins as evaluated by chemometrics

The potential of vibrational spectroscopy and chemometrics as a reliable and fast method for the determination of important gel-forming parameters in amidated pectins has been investigated. For a set of 98 amidated pectin samples, six complete spectroscopic ensembles were recorded including NIR, FT-NIR, FT-IR and NIR FT-Raman spectroscopy. For each spectroscopic ensemble, quantitative models based on partial least squares regression (PLS) have been developed and compared. Chemometric models were constructed by dividing the spectroscopic ensembles up into a calibration set of 73 samples and an independent test set of 25 samples to evaluate the predictive ability of the models. The 98 amidated pectin samples span a degree of esterification (%DE) between 20 and 55% and a degree of amidation (%DA) between 4 and 24 per cent. From all six spectroscopic ensembles quantitative PLS models were obtained for %DE and %DA with RMSEP (root mean square error of prediction) ranging between 1.5 and 2.1 and between 1.1 and 2.1 for %DE and %DA respectively. In both cases the results are comparable to that of the experimental error of the quantitative chemical determination. Finally, different ways of selecting FT-IR spectral elements (variables) to correlate with %DE were compared. The method of principal variables (PV) was found to be superior to methods based on knowledge based selection and the resulting PV-based model was found to be slightly better than the PLS model using the full spectral information.