Chemical and instrumental characterization of pectin from dried pomace of eleven apple cultivars

Pectic substances from eleven samples of dried apple pomace were extracted using an acid procedure (100 mM HNO3, 10 min., 80 degrees C), dried, ground and stored in a P2O5 atmosphere. The degree of esterification was determined by the classical titrimetric method and confirmed by the instrumental FTIR method. The samples showed an average DE of 73% and the typical fingerprint in IR spectrogram. The steric exclusion chromatograms obtained with the multi-angle laser light scattering (MALLS) and refraction index (RI) detectors showed that all samples had a high molar fraction eluted at 36-38 min., another large polysaccharide family had an elution time around 43 min, and some samples showed yet another low molecular oligosaccharide that appeared at 58-60 min. Gas chromatography of alditol acetate allowed estimates of the proportion of the neutral sugar in the samples. The ratio of galacturonic acid and rhamnose may give the average size of the galacturonan fraction. These results showed that yields of pectin extracted by the same acid procedure were slightly different. However, the degree of esterification of pectin was similar, with both factors pointing to the best sources in this group of varieties.