Pectin membranes, degradation

Since the first steps of pectin degradation are extracellular, the intracellular catabolism is dependent on the permeabihty of the membrane to the external substrates. Oligogalacturonides can enter the cells but the corresponding transport system(s) have not yet been identified (14). Two transport systems which mediates entry of monomers were characterised ExuT for galacturonate uptake (35) and KdgT for DKI, DKIl or KDG uptake (36) (Figure 1). 

Pectin degradation in UF-membrane reactors with commercial pectinases... 

Enzymatic degradation of pectin can be satisfactory performed in UF-membrane reactors which have been proved to be helpful tool for laboratory scale investigations. Reaction products can be continuously recovered in a sequence of filtration stages. The obtained product distribution depends on the enzyme to substrate ratio, which affects particularly the... 

To confirm that there was not degradation of pectin, changes in the membrane or changes in PE, UF was conducted at pH 3.8 after initial permeation at pH 8.0 (24). The... 

Oligouronides production in a membrane reactor by enzymatic degradation of pectins from Citrus peel. A preliminary study... 

X. Shao, Y. Fend, S. Hu and R. Govind, Pectin Degradation in a Spiral Membrane Reactor, in Membrane Reactor Technology, R. Govind and N. Itoh (eds), AIChE Symposium Series Number 268, AIChE, New York, NY, Vol. 85, pp. 85-92 (1989). 

For example, the work by Emery and Schroeder (24) indicates that wood can be chemically oxidized with an iron catalyzed reaction under acidic conditions. It is conceivable that this type of treatment could degrade the pit membrane and increase the permeability. Furthermore, Tschernitz (25) has shown that treatment of Rocky Mountain Douglas fir sapwood with hot ammonium oxalate improved the treatability of this material. In this latter case, the ammonium oxalate probably solubilized the pectins in the pit membrane. 

With the objective of enhancing membrane flux by enzymatic degradation of pectin in the puree, the liquefaction enzymes normally used in the process were reduced while a commercial pectinase preparation was used in increasing amounts as a replacement (Table I). 

The vacuole comprising most mature plant cells contains secondary metabolites and enzymes. The cell envelope is composed of cellulosic cell walls bound by pectinaceous middle lamella. A phospholipid-bilayer membrane is located on the inside of the cell wall (plasmalemma), as well as around the vacuole (tonoplast). Disruption of the cell or vacuole membrane leads to the release of hydrolytic enzymes which cause the degradation of pectins or cellulose. This in turn weakens the cell wall and tissue structure and leads to a loss of firmness and crispiness due to a dissipation of the intracellular osmotic pressure (turgor) (Taiz and Zeiger, 2007). 

Chlorophyllases participate in the degradation of chlorophyll and transaminases in the production of precursors for aroma constituents. Demethylation of pectins by pectin methyl esterase (cf. 4.4.S.2) results in the formation of a pectic acid gel, which affects cell membrane permeability, thus resulting in a drop in the rate of oxygen diffusion into leaves during fermentation. 

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