Citrus pectin

The source materials were commercial pectins apple A30 and citrus pectin C73 kindly supplied by Unipectine (France) and Copenhagen Pectin Factory (Denmark) respectively. Polygalacturonic acid samples (named SR) were obtained by acid hydrolysis of a fully de-esterified citrus pectin as previously described [24]. Citrus pectins with different degree of esterification (DE) were obtained by controlled acid de-esterification [8]. 

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. 

Fig. 2. HPLC ion exchange gradient separation of samples (25 ug of uronic acid) of smaller (G7) citrus pectin oligomers (a), larger (G12) citrus pectin oligomers (b), and the B. fruit extract (c). Detection was by PAD. For each sample the peak co-eluting with the standard galacturonate oc-tamer was designated peak 8, and the remaining peaks were numbered consecutively.

Table II. Carbohydrate compositions (weight percentage) of individual oligomer peaks purified (QAE-Sephadex or HPLC ion-exchange separation, respectively) from mixtures of citrus pectin oligomers or B fruit extracts Compositions shown are for peaks whose biological activity is described in Figure 4. Uronic acid values are based on colorimetric assay. Proportions of neutral sugars were determined by GC and adjusted so that totals equal 100%. In fact, some oligomers (G7 peaks 8, 9 and 10. B extract peak 10) produced small (less than 1 % of the total integrated area), unknown peaks in the GC chromatograms.

The exceptionally strong influence of calcium-ions on pectin solutions especially made with HM citrus pectins can be shown by a frequency sweep. The addition of calcium leads to an increase of the complex viscosity. Additionally we can observe a stable trapping of air bubbles in the solution. This effect can not be caused by the increase of viscosity. The frequency sweeps of the solutions give the answer. The storage modulus curves show the significant increase of the elastic shares caused by the addition of calcium-ions. 

Gels made from citrus pectin have a small linear visco-elastic range. To puncture the gels takes a big but only short time effort. The gel breaks into small lumps immediately. In the... 

Figure 4 Phase diagrams of pectins extracted by water from extruded citrus fibre and by acid from the fibres (upper curve), and of commercial citrus pectins (dm 73%) (lower curve)...

Activation studies were conducted at pH 7.5 at 30°C in 20 mL of 0.5% high methoxyl citrus pectin (Citrus Colloids, Hereford, U.K.). Final cation concentration in PE extracts used for activation studies was less than 2 mM as measured by potentiometry. Controls were conducted to correct for non-enzymic alkali consumption, with no polyamine/no PE and polyamine added/no PE. PE activity was normalized as a percentage of activity with no cation addition. 

To improve production of rhamnogalacturonase by Aspergillus aculeatus CBS 115.80 shake flask ejqjeriments were performed on several substrates. Cross reactivity was found after transfer to thamnose in combination with galacturonic acid and on apple pectin, citrus pectin, beet pectin and sugar beet pulp. No cross reactivity was found after transfer to meda containing simple carbon sources such as sucrose, glucose, fiuctose, rhamnose or galacturonic acid. 

Figure 4. Scatchard representation of binding of Ni2+ to pectins in water (A) and in 0.1 M NaN03 (B) at 25°C, with pectins at 2 mequiv. COO-.l-i (V) sugar-beet pectins, (T) citrus pectins.

In water, Scatchard plots showed clear concave-shaped curves whatever the pectin origin (figure 4A). Nevertheless, differences between sugar-beet and citrus pectins appeared in presence of ionic strength. While citrus pectins exhibited convex-shaped curves whatever the metal ion, sugar-beet pectins display convexe curvature for Cu2+ and Pb2+ but concave-shaped curves for the other three cations (figure 4B, in the case of Ni2+). 

Binding isotherms presented the same characterisitics for sugar-beet and citrus pectins according to the pectin concentration and the conditions of ionic strength. The single case of... 

Here data on apple pectins are presented. A comparison of corresponding data on apple and citrus pectins will be given in a future paper. 

Commercial Rapid Set citrus pectin (864 mg galacturonic acid per g, degree of methylation 73) was from SBI (Beaupte, France). 

The FTIR spectra of citrus pectin and wheat straw XRPP (Figure 1) appeared to be similar. Both of the spectra have absorptions at 1740, 1608, 1430, 1360, 1244, 1080, 1060, 1035, 890 and 524 cm. The pectic substances belong to a class of carboxy poly saccharides which differ from neutral polysaccharides, with an intense band in the region 1740 cm l (for salts 1608 cm ) related to vibrations of the carboxyl group... 

Figure 1. FT-IR spectra of citrus pectin (a) and wheat straw xylose-rich pectic polysaccharide (b).

Candida boidinii was cultured at pH 3.51, 5.49 and 7.01, respectively. Czapek s Dox medium with citrus pectin (GENU Pectin, Denmark), sodium pectate or citrus pectin with 20% of D-galactopyranuronic acid (Fluka, Switzerland) as a carbon source were used. The growth curves were performed by measuring the optical density (OD) at 660 nm. 

Total pectinase, cellulase and lipase activities secreted by colonies were detected on BSM plates containing respectively 1% of citrus pectin, 2% Walseth cellulose and 1% olive oil + rhodamine. After few days at 30°C, pectin plates were covered by 1% CTAB for Ihour, positive colonies became surrounded by a clear halo walseth plates are not stained the halo is visible directly on positive clones lipase activity is revealed under UV on oil-rhodamine plates. 

The basal medium of Mandels (Mandels et al., 1976) was used with the following modifications it was buffered with 3 g/1 of sodium nitrate to pH 5.5 and supplemented with 1% w/v citrus pectin " Sigma" or other carbon sources. For enzyme production, 50 ml medium in 250 ml erlemneyer flasks were inoculatedwith spores (10 spores /ml ) exept for the non sporulating Pol 6 strain, where mycelium was used. The culture were incubated at 30° C on a rotary shaker (150 rev mn -1) for 5 days. The culture broth was filtered (Millipore 0.45 pm ) and the supernatant was analysed for pectinolytic activities, reducing sugars and proteins. 

Enzymes produced by parental (CLIOO) and mutant (CTl) strains cultured on citrus pectin... 

The strains were cultured on Mandels medium + 1% citrus pectin for 5 days and the enzymatic activities of culture filtrates were determined on three substrates citrus pectin, polygalacturonic acid and filter paper, (a) extracellular proteins are in p.g/ml. (b) p>ectinolytic activities on pectin (PC) and on polygalacturonic acid (TO) and Pectin esterase (PE) are in units/ml. (c) total cellulolytic activity (filter paper, fp) are in mg of liberated reducing sugars/ml. 

CTl hyperproduces pectinases on "citrus pectin " as well as on "orange peel" local substrate. 

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