FT-IR spectroscopy as a tool for measuring degree of methyl esterification in pectins isolated from ripening papaya fruit

A straightforward method using Fourier transform-infrared (FT-IR) spectroscopy for determination of methyl esterification degree (MED) of pectins is described. The method was used for measuring methylation level of different pectin fractions isolated from papaya (Carica papaya) fruit in three ripening stages as well as of the bulk pectin without isolation from the cell wall. All the samples used were in solid state. MED values were calculated from absorbance spectra of the samples, using a relationship involving absorbance intensities for 1630 and 1745 cm(-1) bands. Under present experimental conditions these bands could be assigned to the stretching frequencies for the carbonyl groups of galacturonic acid and its methyl ester, respectively. The sample quantities required for the technique were less than 1 mg and the results obtained were in agreement with those achieved using an established method. (C) 2002 Elsevier Science B.V. All rights reserved.