Fourier transform Raman and infrared spectroscopy of pectins

The FT-Raman and FT-IR spectra of polygalacturonic (pectic) acid, potassium pectate and its derivatives, as well as commercial citrus and sugar beet pectins were measured and interpreted. Methyl and acetyl esters of potassium pectate derivatives have several characteristic Raman and IR bands that allow both this groups to be distinguished. The very intense Raman band at 857 cm−1 is sensitive to the state of uronic carboxyls and to O-acetylation. The wavenumber of this band decreases with methylation (min. 850 cm−1) and increases with acetylation (max. 862 cm−1). The acetylation of potassium pectate, as well as its acetylation together with methylation, causes drastic changes in the Raman spectra in the region below 700 cm−1. Sugar beet pectin, but not citrus pectin, showed Raman bands at 1633 and 1602 cm−1 and IR band at 1518 cm−1. All these bands rise from feruloyl groups and can be used for identification of pectins containing feruloyl groups.