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

A diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) method was developed to measure the degree of esterification (DE) of commercial pectin samples. The relationship between infrared spectroscopy data and titrimetrically determined DE values was investigated. The ester carbonyl band area (CO) occurring at a mean frequency of 1756 cm−1 had the highest correlation (R2=0.822) with the mean DE of the bands observed. The DE values of pectin samples calculated from the line fit equation were comparable to those obtained from the titrimetric method. Mean DE values obtained were 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 source have to be considered in developing prediction equations using FTIR. DRIFTS can be a rapid, alternative method to titrimetric analysis of pectin DE.