Pectin dissociation

Figure 1. van t Hoff plots demonstrating concentration dependence of pectin dissociation. Values at intercept calculated from end group titrations. 

Maximal speed (Vmax) and supposed Michaelis constant (K ) of pectin hydrolysis reaction (catalyzed by the studied pectinesterase) were determined in Zinewedwer — Berk coordinated, They were determined in the range of substrate concentration values that was below optimum one V = 14.7 10 M min K = 5.56 10 M. The value of dissociated constant (KJ of the triple enzyme—substrate complex was determined from the experimental data at high substrate concentration. It was the following Kj= 0.22 M. Bunting and Murphy method was used for determination. 

At the second critical pH (pH,, ), which is usually below the protein isoelectric point, strong electrostatic interaction between positively charged protein molecules and anionic polysaccharide chains will cause soluble protein/polysaccharide complexes to aggregate into insoluble protein/polysaccharide complexes. For negatively charged weak acid-based (e.g., carboxylic acid) polysaccharides like pectin, with the decrease of pH below the pKa of the polysaccharide, protein (e.g., bovine serum albumin (BSA))/polysaccharide (e.g., pectin) insoluble complexes may dissociate into soluble complexes, or even non-interacted protein molecules and polysaccharide chains, due to the low charges of polysaccharide chains as well as the repulsion between the positively charged proteins (Dickinson 1998). 

Physical Methods. Infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectroscopic methods have been applied to structural analysis of polysaccharides such as pectin. These applications have been reviewed ( ), and reference IR spectra of pectic substances have been published ( ). Quantitative IR has been used to estimate acid dissociation constants of polyuronides from the ratio of -CO2H to -CO2- as a function of pH ( ). Also, by... 

In the case of charged polymers, the charge comes from the dissociation of acid or basic functions. According to the pH, some molecules may be acid (-) or neutral (pectins), or both acid (-) and alkaline (-I-) (proteins). Proteins have both functions, with an isoelectric pH (or isoelectric... 

Pectin is also found to form aggregates of macromolecule at acidic pH whereas at neutral pH it tends to dissociate and shows an expanded network. Rate of gelation is also influenced by the DE. When DE is reduced via the treatment with commercial pectin methyl esterase an increase in viscosity and firmer gelling was found in the presence of calcium ions [49, 77]. Furthermore, amidation process increases the gelation ability of LM pectin and the amidated pectin requires less calcium to gel [8,75,6,76],... 

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