Isolation and structural characterization of a pectin homo and ramnogalacturonan

With a purpose to achieve an individual components of the pectins there was purified and separated the acidic components of the apple pectin and its chemical structure was studied using C-13-NMR-Spectroscopy. The apple pectin was consecutively subjected to processing with hydrochloric acid and ethanol mixture, ultracentrifuging at 7000 and 40 000 rpm, ultrafiltration, fractionation on cellulose (DEAE-52) ion exchanger, eluting by the phosphate buffer. The contents of the acidic and neutral polysaccharides in an initial pectin and in the selected fractions controlled by narrow-band filter - spectroscopically in relation to E-q = E-298 / E-315. In the C-13-NMR-spectrums of the pectins before purifications on the ion exchanges besides the signals characteristic for homogalacturon, resonances are observed at 105.8, 79.01, 76.3, 73.9, 70.0 and 18.32 m.d., appropriate to the ramnogalacturonan residues. Resonance lines of acidic fraction in the field of 69.8, 70.6, 72.3, 80.6, 100.6 and 176.6 m.d, are referred to homogalacturonan residues and signals at 55.9, 73.3, 80.8, 101.6 and 172.6 m.d. to their methoxyl group. Minor resonance at 18.32 originated from C-6 rhamnose residues, substituted or unsubsituted with galactosyl-chains. Hence it has been shown that the apple pectin consist mainly of linear homogalacturonan and branched ramnogalacturonan macromolecules. (C) 2000 Elsevier Science B.V. All rights reserved.