Pectins deesterification

The activity of PE was measured [25] from the increase of carboxylic groups during the pectin deesterification (5 g/L) in phosphate-citrate buffer 50 mM, pH 4.7. Continuous titration of the reaction mixture with NaOH 0.01 M was employed for product determination. 

Gelation became a significant problem with the introduction of frozen orange juice concentrate, which initially was often packed without pasteurization. This product, when not frozen, rapidly developed low ester pectins by virtue of the PE it contained. Much of the research generated in response to this problem has been reviewed by Joslyn and Pilnik (22). Briefly, it has been found that gelation is the result of pectin deesterification (23), and increases as juice pulp (24), PE... 

Fig. 10. Intercellular junction zones of carrot cells grown in suspension have been observed in electron microscopy after immunogold labeling with the 2F4 antibody, (a) no treatment of the sections prior to labeling the gold particles are restricted to the center of the junction zones (b) enzymatic (pectin methyl esterase) deesterification of the E.M. grids before labeling the deesterified pectins present in the primary walls now bind the probe. Scale bars = 1 pm.

When cell-wall fragments are incubated in molar NaCl, ionically bound proteins are released into the incubation medium. All investigated crude cell extracts deesterified Citrus pectin (Table 2) but the deesterification rates were clearly higher when the enzymes were still bound to the cell walls, indicating a major loss of activity during the solubilization process. 

Qualitatively, the results observed with ferric chloride and lead acetate were highly variable. It was first noted with ferric chloride that gels were forming within the reaction vessel We observed the formation of translucent gels in the reaction vessel with calcium chloride, spermidine and ferric chloride. In the case of lead acetate, a feathery type precipitate formed in the reaction vessel. Macdonald et al. (14) observed formation of a clear gel and flocculated precipitate in high ester pectin treated with lemon endocarp and peel PE isozymes, respectively. They hypothesized that the different gel structures were due to unique mechanism of deesterification by the PE isozymes. Our results with different cations and formation of different gel structure or precipitate seems to be similar to that reported by Macdonald et al. (14). If there is a different mechanism of de-esterification for plant PEs,... 

DM and DAc of various pectin fractions except those of OHSP (due to deesterification during extraction) are summarized in Table 5. The DM of WSP of conventionally canned carrots did not significantly differ from that of fresh carrots,while in the presence of CaCk a considerable increase was observed. This increment can be ascribed to cross-Unking of water soluble-low methylated... 

The deesterification of pectin with ammonia has industrial application because of the following reasons ... 

Reistma et al. [2] establish the positive influence of NaCl on the deesterification of ester groups of amidated pectins with ammonium hydroxide, without discussing the mechanism of the catalytic action of the sodium chloride. 

The behaviour of the added alkali cations is different. Na and K enhance the deesterification and the differences in the interaction of both cations at the separate reactions are inessential. The use of these ions in the deesterification of highly esterified pectin in either enzyme or chemical method shows that they only enhance the hydrolysis. Since in the investigated case they cannot influence the equilibrium (6), the enhancement of the hydrolysis leads to faster exhausting of the reactable -COOCH3 groups and thus is reduced the rate of the competitive ammonolysis. 

This study reports on the production of pectic enzymes and partial characterization of polygalacturonases produced by Candida boidinii. Candida boidinii belongs to the so called methylotrophic yeasts with famous utilization of methanol. Pectin, the natural substrate of pectic enzymes complex, can serve for microorganisms as a C - source by two different ways after deesterification with pectinesterase as methanol and after hydrolytic cleavage with... 

Deesterification of natural polysaccharides accomplishes the same result as chemical derivatization, to wit, the critical DE range necessary for high-methoxyl pectin gelation. Robinson et al. (1988) discovered that the normally gelling, branched polysaccharides studied did not gel when side chains were removed, because the unsubstituted main chain did not subsequently adopt an ordered conformation. Their explanation was that the polydispersed... 

PME activity is almost not affected in the usual pressure range up to 600 MPa [7]. In the intact cell, PME is bound to the cell wall, upon HP-application PME is liberated and gets into contact with its substrate the highly methylated pectin. This causes a de-esterification not only during the HP-application, but a continuous further deesterification can be observed after release of the pressure [8]. Therefore, the tissue hardening and poor cooking behaviour is even more pronounced after a storage of 3 - 4 days (fig. 5, 6). 

Depolymerization splits ester linkage. Deesterification forms unsaturated monomers of galacturonic acid. With pectin degraded, hemicellulose is exposed. 

Pectinesterase action was first reported in 1840 by Fremy (56). He noted that the addition of carrot juice to a pectin solution caused formation of a gel. This gel was produced by the enzymatic deesterification of pectin followed by precipitation of the resulting polygalacturonic acid as calcium pectate 20), Various names such as pectin meth-oxylase and pectin methyl esterase have been applied to the enzyme, but pectinesterase is the preferred trivial name (57). 

Multiple forms of pectinesterase have been reported. Reid (64) separated two active pectinesterase fractions from a fungal source and suggested that pectinesterases from various organisms diflFer in their initial rates and final percent deesterification of pectin. Glasziou and Inglis (65) found two pectinesterases present in tobacco pith one of which was firmly bound to the cell walls. Hulton and Levine (66) observed three molecular forms of pectinesterase in the pulp of the... 

Kirtchev, N., Panchev, I. and Kratchanov, C. 1989. Kinetics of acid-catalyzed deesterification of pectin in a heterogeneous medium, Int. J. Food Sci. Technol., 24 479-486. 

---