Turbidity, polysaccharides

Avigad and Milner224 used a turbidimetric method based on the measurement of residual turbidity caused by complexing the acid polysaccharide with such quaternary ammonium detergents as cetyl-pyridinium bromide. The activity unit was expressed as the amount of enzyme bringing about a decrease of absorbance at 400 nm of 0.01/min. 

Dirt, soils, and clays Retention of particulates and colloids in turbid water supplies concn of fines in kaolin processing Polysaccharides and oligosaccharides Concn of starch effluents concn of pectin extracts... 

Figure 4 Thermal stability of lysozyme-polysaccharide conjugates. O, lysozyme , lysozyme-dextran conjugate , lysozyme-galactomannan conjugate. Lysozyme-polysaccharide conjugates were prepared by dry heating at 60°C for 2 weeks. Sample solutions (0.1%) in 67 mM phosphate buffer (pH 7.4) were heated at an increasing rate of l°C/min. The resulting turbidity was measured with the absorbance at 500 nm.

The ethanol test (Boulton etal., 1996) consists of adding a volume of absolute ethanol to the same volume of wine. The turbidity formed in the presence of alcohol, measured by nephelometry shortly after the substances are mixed, does not consist only of unstable proteins, as polysaccharides and particularly mannoprotein also precipitate. It is relatively common for wines that are perfectly thermostable to become turbid when subjected to this ethanol test, particularly if they have acquired a high mannoprotein content through aging on the lees. This test leads to the use of higher doses of bentonite than are truly necessary to achieve stability. 

Most turbidity occurring in wine is due to the flocculation of colloidal particles caused by chemical reactions that leave the solution clear. It is certain that the presence of natural polysaccharides, with their protective colloid properties, prevent the formation of turbidity and deposits. It is also clear that, in some cases, it may be useful to enhance this protective effect by adding a colloid such as gum arabic. 

Nevertheless, this does not provide a sufficient explanation for the differences observed in wines. When kaolin gel is added, certain wines remain very turbid, whereas others are properly clarified. The presence of protective colloids in the medium (Section 9.4.2) is the decisive factor in hindering clarification, causing these differences in behavior. Colloids in wine consist mainly of long-chain polysaccharides that form networks, preventing sedimentation and clogging filters. 

As bentonite flocculates in wine, with a behavior analogous to that of protein fining agents, experiments have been made in using it to clarify wine. In fact, its effectiveness in clarification depends on the type of bentonite and the composition of the wine. The only wines that may be properly clarified are reds or whites with low concentrations of polysaccharides and other protective colloids (Section 9.4.1), as these inhibit the flocculation and settling of the bentonite particles. In some winegrowing areas, bentonite is well suited to clarifying dry white wines, but elsewhere white wines may be more turbid after bentonite treatment than before. 

Table III shows the results obtained with two crystalline preparations of the polysaccharide. Single crystals and a "quench precipitate" (prepared by quickly chilling a polymer solution in ice to precipitate the polysaccharide with minimal crystallinity) were compared. The extent of degradation of lamellar crystals is highly temperature dependent, with the total fraction of polymer digested at any temperature being finite and quite reproducible from one batch of crystals to another. Incubation up to 20 hours causes no additional decrease in turbidity nor do the crystals inactivate the enzyme. The plateau in absorbance is evidence of a "two region" model of crystal morphology, i.e., one with both accessible and inaccessible zones. The extent of digestion at 20°C of the lamellar crystalline material is to be compared with that of the "quench precipitate" form at the same temperature.

Insoluble polysaccharides like cellulose can be suspended and mixed with agar. This will result in turbid plates. If the polysaccharide is degraded clear zones around the colonies will emerge (6). This method can also be used with soluble polysaccharides. However, large amounts may be needed to obtain sufficient turbidity. Furthermore, the presence of protein contaminants can also cause turbidity. Thus, colonies producing proteases instead of polysaccharases may be selected. 

In the case of dextran (0.1-1%) and amyiopectin (0.05%) the potentiometric measurements do not indicate any interaction with NaDS, the activity of NaDS solutions is the same with and without these polymers. An amylose solution of 0.025% was turbid and it did not clear up even in the presence of 20 mmoLkg" NaDS. However, the potentiometric measurements showed binding of NaDS according to a Langmuir isotherm with a saturation value of 0.27 mmol/g amylose. The binding of NaDS on amylose is regarded as an adsorption on solid amylose particles and not as an interaction between them in solution. It is concluded that the investigated polysaccharides do not interact with NaDS in aqueous solution. 

Fig. 2. A typical example of gel-filtration of liposomes coated with FITC(0.54)-OPP-50(1.8) from the free FITC-OPP developed with 200 mM Tris-HCl (pH 8.0) as an eluant. Liposomes were detected by turbidity at 220 nm (— —) and fluorescence intensity of FITC moiety at 520 nm (—O —) Coating with the polysaccharide was perfomed by incubating 3.0 ml of a sonicated liposome suspension prepared from 30 mg of egg lecithin with 1 ml of 200 mM Tris-HCl containing 5 mg of the FITC-OPP at 25 C (see text).

Miscellaneous Polysaccharides and Oligosaccharides.—The reaction of acidic polysaccharides with cetyltrimethylammonium bromide has been studied by recording the turbidity with an automatic titration device." The optimal conditions for the quantitative determination of various acidic polysaccharides were found from a correlation between ionic strength and turbidity. 

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