Pectins molecular weight

Figure 3 Effect of ionic calcium addition on average droplet sizes dA3 and creaming stability of D-limonene emulsions (10 vol% oil, ionic strength 0.2 M, pH 4.7) stabilized by depolymerized pectin molecular weight 70 kg/mol...

When appreciable amounts of pectin, proteins, lipids, unwanted polyphenols, or other compounds are suspected to be present in anthocyanin-containing extracts, some of them can be precipitated or the anthocyanins may be crystalhzed and separated from the others. Pectin and proteins can be removed by organic solvents such as methanol and acetone in order to reduce their solubility, then precipitated and separated by centrifugation. Gelatin was used to remove proanthocyanidin due to its high molecular weight. Anthocyanins were reported to be precipitated early by lead acetate to achieve isolation from other materials. ... 

Whatever Is the technic used to determine the molecular weights on pectins, it is necessary to eliminate aggregates often mentionned in the litterature [13, 19, 21-23] for this, ultracentrifugation was used but it seems that filtration through hydrophilic membranes with very small pores (as low as 0.1 or 0.05 pm) is easier. 

At the moment, one recommends to determine the molecular characteristics of pectins using SEC chromatography equipped with a differential refractometer, a multiangle laser light scattering detector and a viscometer as previously described [25]. This technique needs no calibration with the usual molecular weight standards such dextrans and pullulans... 

The viscosity of sodium pectinate was previously examined by Pals and Hermans [44]. In salt excess (NaCI 0.1 M), the viscosity of a pectate sodium form solution (ri) is related to the polymer concentration (c) and the molecular weight (or [rj] = KM ) by the relation ... 

The observed increase in serum and efflux viscosity of juice from transgenic tomato fruits was most likely due to changes in pectin chemistry as a result of reduced levels of PME activity. Since viscosity is affected by the volume occupied by the molecule or the extent of molecular association in solution, both molecular weight and DOM will enhance the viscosity of the juice [26]. Since juice from... 

Further characterization by SDS-PAGE and Western blot analysis of the culture filtrate of a 6 day-old culture of lindemuthiaimm showed that only one endoPG of the same molecular weight (42 kDa) as the pure endoPG (Hugouvieux et al., 1995) was induced on pectin. 

Pectins are longchain macromolecules. In aqueous solutions they form more or less stiff rods or coils, depending on their degree of branching and linking as well as their molecular weight. In addition interparticular or intermolecular physical-chemical interactions like Van-der-Waals forces, ionic interactions or hydrogen bonds influence the active volume of the molecule, the stiffness and the viscosity. 

The value of critical concentration depends strongly on the pectin being used. Figure 2 gives the viscosity curves of two different pectins at the same concentration of 2.5 % w/w. The different production parameters, that have been used for these pectins, have strongly influenced their flow behaviour. The enzymatic reduction of the molecular weight down to... 

Figure 2. Viscosity curves of pectins with different molecular weight (2.5 % sol)...

The results showed (16) that the extruded products contained a large amount of water soluble pectins of high molecular weight which were able to gel. It has been shown that the all the extruded citrus fibres were able to gel in presence of sucrose at acidic pH without prior extraction of the pectins. 

Each fruit has specific quantities and ratio of pectin, hemicelluloses and cellulose. These polysaccharides are important concerning enzymes activities required to produce juices and concentrates. Moreover, even if molecular weight and methylation degree of the pectin are specific for each fruit, during the fruit maturation, endogenous pectinases depolymerases and esterase are changing the pectin characteristics This broad variability of raw material makes difficult the standardisation of fruits processing. 

For apple maceration, the main activity is the endopectinlyase (PL) which decreases the viscosity due to the colloidal pectin by decreasing tlie molecular weight of this substrate methylated at about 90%. In association to this PL, exo B and endoarabanase (ARAs), pectinacetylesterase (PAE), rhamnogalacturonase (RG) and other hemicellulases allow to hydrolyse side chains of the pectin, decrease the steric hindrance and make the access of pectinases to the rhamnogalacturonic backbone more easy. 

Ultrafiltration of heterogenous colloidal suspensions such as citrus juice is complex and many factors other than molecular weight contribute to fouling and permeation. For example, low MW aroma compounds were unevenly distributed in the permeate and retentate in UF in 500 kd MWCO system (10). The authors observed that the 500 kd MWCO UF removed all suspended solids, including pectin and PE. If PE is complexed to pectate in an inactive complex, then it is conceivable that release of PE from pectin with cations will enhance permeation in UF. At optimum salt concentration, less PE activation was observed at lower pH values than at higher pH (15). In juice systems, it is difficult to separate the effect of juice particulates on PE activity. Model studies with PE extracts allows UF in the absence of large or insoluble particulates and control of composition of the ultrafilter. In... 

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