Gels pectate

In contrast, observation of the c.d. with the addition of Ca(OH)2, as a function of d.p., demonstrated that terminal and central units react differently towards Ca ". This is illustrated in Fig. 27 for the dimer and the polymer. Again, the intensity of the c.d. band decreases as the polymer binds calcium and begins to gel. Results for both salt forms are attributed to a helix having a two-fold screw-symmetry, in analogy with calcium pectates. The gelling would then involve a multi-chain association, with crosslinking by the calcium ions to form an egg box structure. ... 

The rheological behaviour in the range of LM pectin was analyzed and the sol-gel diagram established [59] for different stoichiometric ratios. In their paper, these authors determined the gel times for sodium pectate during calcium-induced gelation and the variation of the gel time with polymer concentration, stoichrometric ratio and temperature. 

At end, it is important to mention that calcium pectate gel beads were compared with calcium alginates gel beads for all entrapment uses [65, 66] in this work, the authors determined the pore size of the beads by size exclusion chromatography using dextran standards and other solutes. 

Figure 7. The egg-box structure for the junction zones of dilute calcium pectate gels two galacturonan chains in the twofold (2i) helical conformation with calcium ions (shaded circles) locked between them.

Figure 9. The cable model for the structure of concentrated calcium pectate gels. Egg-box dimers link single-chains segments (top left) and are themselves ed together by larger aggregates of either egg-box or 3i helical chains (lower right)...

F ure 10. solid-state NMR spectra of calcium pectate in the solid (A) and gel (B) forms. Inset resolution-enhanced spectra. The gel concentration was 290 g/1. 

Thus pectins in muro contain most elements of the cable model but have additional features due to esterification (acetyl- as well as methyl-) and branching. The ionic junction zones are similar to those of calcium pectate gels in vitro but also contam methyl-esterified junctions, and most of the single chains probably have a relatively high degree of methyl-esterification. 

Figure 4. Isoenzyme profiles of wild type and mutant strains. Detection of PG activity was by ruthenium red staining on pectate-agarose overlay gels after lEF. WT indicates wild type and the numbers refer to specific mutant isolates.

Macmillan and coworkers51 105 106 purified pectinesterase produced by Clostridium multifermentans by using practically all of the available methods and materials (calcium phosphate gel, DEAE-cellulose, DEAE-, QEAE-, CM-, and SE-Sephadex, Sephadexes G-75, G-100, G-150, and G-200, Sepharose 4B, and zonal centrifugation). However, they could not separate pectinesterase from exo-pectate lyase, and, hence, they postulated that either (a) a complex of the two enzymes having an apparent molecular weight of 400,000 exists, or (b) the two enzymes are identical in their molecular species. On the basis of the mode of action of this pectinesterase in comparison with that of those from tomatoes and from Fusarium ox-ysporum, the existence of a complex of pectinesterase and exopectate lyase in Clostridium multifermentans appears to be the more probable. 

The development of modem separation techniques has affected the purification procedures employed for D-galacturonanases. Fractional precipitation with ammonium sulfate and with organic solvents are now used only in combination with new separation techniques. To separate fractions having D-galacturonanase activity, adsorption to pectate or calcium pectate gel has been used in several instances.157-207... 

If steps are not taken to stabilize cloud, most citrus juices will clarify when allowed to stand. Clarification occurs when native PE lowers the ester content of juice soluble pectin until it becomes susceptible to precipitation as insoluble pectates (23). If pectin levels are high enough, as in concentrates, these pectates may form a gel. 

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