Determination of polygalacturonic acid content in pectin extracts by diffuse reflectance Fourier transform infrared spectroscopy

A simple, rapid diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) method was developed for pectin measurement. Pectin calibration standards were prepared by blending polygalacturonic acid with potassium bromide to cover a range of polygalacturonic acid concentrations (10–98%). A linear relationship between pectin content and total carbonyl absorption band area was found (R²=0.982). Linearity was up to 80% pectin, since there was no significant difference in peak areas of 80% and greater. Pectin contents of various commercial pectin samples were calculated from the linear fit equation. Accuracy of the DRIFTS method was determined by comparing the pectin contents to the values obtained by colorimetric and HPLC methods. For four different sources of samples, the pectin contents by FTIR method were 78.2, 89.4, 65.9 and 67.1%, which were comparable to values obtained by colorimetric analysis (79.1, 87.9, 64.7 and 57.7%) and HPLC (84.1, 91.4, 69.5 and 67.9%).