<p>Cell wall pectic substances have a great influence on the production and quality aspects of apple juice. Apple juices were characterized by their polysaccharide content and composition. A pectic fraction, retained by ultrafiltration of a liquefaction juice, was isolated and termed MHR (modified hairy regions). MHR, resistant to further enzymic degradation by the liquefaction enzymes, was characterized using chemical and enzymic methods. Next to a high arabinose content, this fraction was characterized by a high rhamnose to galacturonic acid ratio and a high acetyl content. Rhamnogalacturonase (RGase), an enzyme able to hydrolyze galacturonic acid-(1->2)-rhamnosyl linkages within the rhamnogalacturonan backbone, was purified and characterized.<p>Next to high molecular weight degradation products, rhamnogalacturonase released characteristic oligosaccharides from MHR. Various 2D-NMR techniques were used to identify these RGase oligomers, which consisted of a tetrameric or hexameric backbone of alternating rhamnose and galacturonic acid residues with a galactose residue substituted at C-4 of part of the rhamnose moieties.<p>Analogous MHR fractions were isolated from potato fibre, pear, carrot, leek, and onion tissue, although variations occurred with respect to the arabinose and xylose content. All MHR fractions were degraded by RGase in a comparable fashion resulting in the same type of oligomers in an almost equal ratio.<p>Comparison of the MHR with non-modified pectic hairy regions of apple cell wall, isolated in a mild and defined way, revealed great resemblance indicating that the modifications of the MHR during enzymic liquefaction were only minor. The oligomers liberated by RGase from the various pectic hairy regions differed in absolute as well as in relative amount.<p>After degradation by RGase of the highest molecular weight population of apple MHR, three subunits were characterized representing a xylogalacturonan segment, residual stabs of the backbone rich in arabinose and regions of alternating rhamnose-galacturonic acid residues of unknown length. The substitution of xylose residues and methylestergroups over the galacturonan backbone was studied by NMR and was found to be random.
|Qualification||Doctor of Philosophy|
|Award date||16 Jun 1995|
|Place of Publication||S.l.|
|Publication status||Published - 1995|
- apple juice
- organic compounds