Proteins colloid stability

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

Molina-Bollvar, J.A., Galisteo-Gonzalez, F., and lvarez, R.H. (1998) Anomalous colloidal stability of latex-protein systems./. Colloid Interface Sci. 206, 518-526. 

The sorbent materials are supplied as finely dispersed colloidal particles, whose surfaces are smooth. Some of their properties are presented in Table 3. The sorbents cover different combinations of hydrophobicity and sign of the surface charge. Thus, the model systems presented allow systematic investigation of the influences of hydrophobicity, electric charge, and protein structural stability on protein adsorption. 

BSA, sterie considerations in protein adsorption, 180-82 on CE from aq. NaCl, 95-111 colloidal stability in nonaq. media, 332... 

In a qualitative way, colloids are stable when they are electrically charged (we will not consider here the stability of hydrophilic colloids - gelatine, starch, proteins, macromolecules, biocolloids - where stability may be enhanced by steric arrangements and the affinity of organic functional groups to water). In a physical model of colloid stability particle repulsion due to electrostatic interaction is counteracted by attraction due to van der Waal interaction. The repulsion energy depends on the surface potential and its decrease in the diffuse part of the double layer the decay of the potential with distance is a function of the ionic strength (Fig. 3.2c and Fig. 

Polymer brushes were found to minimize adsorption of proteins by the soft or steric repulsion of the flexible yet immobihzed macromolecules [179], although a generally valid explanation of the protein resistant properties of some hydrophihc brushes is not available. A similar explanation can be formulated for the improvement of the colloidal stability of particle suspensions, when polymer brush-type layers are bound to small particles. This and other intriguing features of polymer brushes prompted a remarkable experimental and theoretical research activity in order to understand and exploit the unique properties of polymer brushes. 

McMurrough, I., Kelly, R., and Byrne, J. (1992). Effect of the removal of sensitive proteins and proanthocyanidins on the colloidal stability of lager beer. J. Am. Soc. Brew. Chem. 50, 67-76. 

Marinova, K., Gurkov, T., Velev, O., Ivanov, I., Campbell, B., Borwankar, R. (1997). The role of additives for the behaviour of thin emulsion films stabilized by proteins. Colloids and Surfaces A Physicochemical and Engineering Aspects, 123-124, 155-167. 

Key points relating to the adsorption behaviour of proteins and their influence on colloid stability are summarized below (Dickinson, 1999a). 

Izmailova, V.N., Yampolskaya, G.P., Tulovskaya, Z.D. (1999). Development of Reh-binder s concept on structure-mechanical barrier in stability of dispersions stabilized with proteins. Colloids and Surfaces A Physicochemical and Engineering Aspects, 160, 89-106. 

Filtering. Conditioning or lagering gives the beer its desired organoleptic properties, but it still contains yeast, protein-tannin complexes, etc, ie, it has a hazy appearance. A high quality beer must be clear and totally sterile, have colloidal stability, and yeast must be removed to allow the beer to have biological stability. The protein-tannin complexes must also be removed so as not to upset the colloidal stability. 

A current hypothesis, which is receiving considerable attention, is that one can indeed produce a surface which actively repels proteins and other macromolecules123 124, 133). The basic idea is presented in Fig. 25, which shows that a neutral hydrophilic polymer, which exhibits considerable mobility or dynamics in the aqueous phase, can actively repel macromolecules from the interface by steric exclusion and interface entropy methods. This method has been well-known and applied in the field of colloid stability for many years 120). The most effective polymer appears to be polyethylene oxide, probably because of its very high chain mobility and only modest hydrogen bonding tendencies 121 123>. 

Fig. 25a and b. A protein resistant surface based on the steric repulsion argument commonly used in the colloid stability field U0). The interaction between a polyethylene oxide grafted surface and a protein solution is shown, a. suggests an excluded volume or steric repulsion mechanism b. the surface dynamics or polymer chain motion mechanism (from Ref., 33))... 

Dickinson, E. (1993). Protein-polysaccharide interactions in food colloids. In Food Colloids Stability and Mechanical Properties, Dickinson, E., and Walstra, P. (Eds.), pp. 77-93. Royal Chem. Soc., London. 

There are some qualitative difficulties when the specific ion effects are explained via the dispersion forces of the ions. Particularly the anions, for which the dispersion coefficients / , are large, affect the double layer interactions. However, experiments on colloid stability [6] or colloidal forces [11] revealed strong specific ion effects especially for cations. Furthermore, the ions which affect most strongly the solvating properties of the proteins are those from their vicinity, since they perturb mostly the structure of water near the proteins. However, the van der Waals interactions of ions predict that the cations remain in the vicinity of an interface, and the anions are strongly repelled, while Hofmeister concluded that anions are mainly responsible for the salting out of proteins. 

It is claimed that commercially-available ultrasound equipment can measure the following quality parameters of dairy products levels of solids, solids non-fat (SNF), protein, water and fat solid fat content (SFC), colloidal stability, gelation point, adulteration with oil, particle size, particle size distribution, oil composition, protein denaturation and fat oxidation. This incomplete list represents an impressive contribution towards the solution of food quality measurement although the present authors are slightly skeptical regarding some of these claims. In this review only those applications will be addressed which are regarded as robust. 

K-casein also contains two Cys residues per monomer subunit and is thus capable of interacting with the whey proteins, e.g., mainly g-lactoglobulin, via the disulfide interchange mechanism at temperatures at or above 65°C. This latter phenomenon is believed to be important in providing colloidal stability to the milk casein micelle system, as well as to the whey proteins, in high temperature processed milk products. It has also been postulated that this latter interaction with g-lactoglobulin may alter the availability of K-casein in the micelle, and thus has a detrimental effect upon the cheese making properties of milk (4). 

Electric double layers at phase boundaries pervade the entire realm of Interface and colloid science. Especially in aqueous systems, double layers tend to form spontaneously. Hence, special precautions have to be taken to ensure the absence of charges on the surfaces of particles. Insight into the properties of double layers is mandatory, in describing for Instance electrosorption, ion exchange, electrokinetics (chapter 4), charged monolayers (Volume III), colloid stability, polyelectrolytes and proteins, and micelle formation of ionic surfactants, topics that are intended to be treated in later Volumes. The present chapter is meant to Introduce the basic features. 

Where membrane filtration is applied in the wine production process can also have long terms effects. Care should be taken to ensure that long term colloidal stability as a result of membrane filtration is not a problem. It may take several months for the colloids to reestablish new equilibrium. Proteins, anthocyanins, tannins and tartrate salts may precipitate. 

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