Determination of pectin degree of esterification by diffuse reflectance Fourier transform infrared spectroscopy

A diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) meth od was developed to measure the degree of esterification (DE) of commercial pectin samples. The relationship between infrared spectroscopy data and ti trimetrically determined DE values was investigated. The ester carbonyl ban d area (C=O) occurring at a mean frequency of 1756 cm(-1) had the highest c orrelation (R-2 = 0.822) with the mean DE of the bands observed. The DE val ues of pectin samples calculated from the line fit equation were comparable to those obtained from the titrimetric method. Mean DE values obtained wer e within 3.23% for DE 71.6, 2.9% for DE 62, and less than 1% for DE 55.3 of values obtained by titrimetric method. Spectral variations due to sample s ource have to be considered in developing prediction equations using FTIR. DRIFTS can be a rapid, alternative method to titrimetric analysis of pectin DE. (C) 1999 Elsevier Science Ltd. All rights reserved.