Phase separation protein + polysaccharide

It did not give rise to phase separation or precipitation. Similar behavior was observed when other types of polysaccharides were examined [53,54]. By now all the commercially important polysaccharides have been applied to the fabrication of hybrid silica nanocomposites in accordance with Scheme 3.2. What is more, various proteins have been entrapped in silica by the same means. In all instances the THEOS demonstrated good biocompatibility with biopolymers, even though its amount in formulations was sometimes up to 60 wt%. Biopolymer solutions after the precursor admixing remained homogeneous to the point of transition into a gel state. 

The ethylene glycol-containing silica precursor has been combined, as mentioned above, with most commercially important polysaccharides and two proteins listed in Table 3.1. In spite of the wide variety of their nature, structure and properties, the jellification processes on addition of THEOS to solutions of all of these biopolymers (Scheme 3.2) had a common feature, that is the formation of monolithic nanocomposite materials, proceeding without phase separation and precipitation. The syner-esis mentioned in a number of cases in Table 3.1 was not more than 10 vol.%. It is worthwhile to compare it with common sol-gel processes. For example, the volume shrinkage of gels fabricated with the help of TEOS and diglyceryl silane was 70 and 53 %, respectively [138,141]. 

In addition to classical reverse phase separation of peptides on octadecyl derivatized silica monoliths, sugars and peptides as well as proteins and nucleosides have been analyzed on a 20-cm-long silica-based poly(acrylic acid) column (ID. 200 pm), employing HILIC and weak cation-exchange chromatography, respectively [194]. Furthermore, HILIC fractionation of polysaccharides delivered remarkable and promising results [84,194]. 

Tuinier, R., Dhont, J.K.G., de Kruif, C.G. (2000). Depletion-induced phase separation of aggregated whey protein colloids by an exocellular polysaccharide. Langmuir, 16, 1497-1507. 

Nowadays it is well established that the interactions between different macromolecular ingredients (i.e., protein + protein, polysaccharide + polysaccharide, and protein + polysaccharide) are of great importance in determining the texture and shelf-life of multicomponent food colloids. These interactions affect the structure-forming properties of biopolymers in the bulk and at interfaces thermodynamic activity, self-assembly, sin-face loading, thermodynamic compatibility/incompatibility, phase separation, complexation and rheological behaviour. Therefore, one may infer that a knowledge of the key physico-chemical features of such biopolymer-biopolymer interactions, and their impact on stability properties of food colloids, is essential in order to be able to understand and predict the functional properties of mixed biopolymers in product formulations. 

In Part Four (Chapter eight) we focus on the interactions of mixed systems of surface-active biopolymers (proteins and polysaccharides) and surface-active lipids (surfactants/emulsifiers) at oil-water and air-water interfaces. We describe how these interactions affect mechanisms controlling the behaviour of colloidal systems containing mixed ingredients. We show how the properties of biopolymer-based adsorption layers are affected by an interplay of phenomena which include selfassociation, complexation, phase separation, and competitive displacement. 

In view of the importance of chiral resolution and the efficiency of liquid chromatographic methods, attempts are made to explain the art of chiral resolution by means of liquid chromatography. This book consists of an introduction followed by Chapters 2 to 8, which discuss resolution chiral stationary phases based on polysaccharides, cyclodextrins, macrocyclic glyco-peptide antibiotics, Pirkle types, proteins, ligand exchangers, and crown ethers. The applications of other miscellaneous types of CSP are covered in Chapter 9. However, the use of chiral mobile phase additives in the separation of enantiomers is discussed in Chapter 10. 

Both polymeric and silica-based columns are in common use.The polymeric columns are heavily used in the analysis of synthetic polymers and plastics where organic solvents are required. Silica-based columns with hydrophilic bonded phases are used to separate aqueous solutions of macromolecules. Finally, polymeric size-separation columns with hydrophilic phases are available for separation of polysaccharides, peptides, and very small proteins. 

Persson and Andersson [65] reviewed the unusual effects in liquid chromatographic separations of enantiomers on chiral stationary phases with emphasis on polysaccharide phases. On protein phases and Pirkle phases, reversal of the elution order between enantiomers due to... 

The mixture of phenol and water (45 50, v/v) can be used to extract LPS (Westphal and Jann, 1965). This mixture is a single phase above 65°C but separates into two phases below 65°C. LPS and proteins can be extracted from bacteria by this mixture above 65°C. When cooled down, phase separation occurs. The phenol phase mainly contains proteins, while the water phase contains LPS, polysaccharides, and nucleic acids. The following protocol is the most used for phenol-water extraction of LPS (Johnson and Perry, 1976). 

On mixing solutions of a protein and a polysaccharide, four kinds of mixed solutions can be obtained. Figure 3.1 shows that two single-phase systems (1 and 3) and two-types of biphase systems (2 and 4) can be produced. The two-phase liquid systems 2 and 4 differ in the distribution of biopolymers between the co-existing phases. The biopolymers are concentrated either in the concentrated phase of system 2 because of interbiopolymer complexing, or within separated phases of system 4 because of incompatibility of the biopolymers. The term biopolymer compatibility implies miscibility of different biopolymers on a molecular level. The terms incompatibility or limited thermodynamic compatibility cover both limited miscibility or limited cosolubility of biopolymers (i.e., system 2) and demixing or phase separation... 

The phase separation threshold is lower for systems containing a branched polysaccharide than for systems containing a linear polysaccharide of the same molecular weight. It is higher for globular proteins compared to proteins of unfolded structure. An increase in excluded volume means a decrease in the free volume of the solution accessible for biopolymers. Thus, the excluded volume of biopolymer molecules implies that water in real foods can be nonsolvent water relative to macromolecules. 

The binodal branches do not coincide with the phase diagram axes. This means that the biopolymers are limitedly cosoluble. For instance, on mixing a protein solution A and a polysaccharide solution B a mixture of composition C can be obtained. This mixed solution spontaneously breaks down into two liquid phases, phase D and phase E. Phase D is rich in protein and E is rich in polysaccharide. These two liquid phases form a water-in-water (WIW) emulsion. Hie phase volume ratio is estimated by the inverse lever rule. The phase D/phase E volume ratio equals the ratio of the tieline segments EC/CD. Point F represents the phase separation threshold, that is, the minimal critical concentration of biopolymers required for phase separation to occur. 

Biopolymer incompatibility seems to provide phase-separated liquid and gel-like aqueous systems. In highly volume-occupied food systems aggregation, crystallisation and gelation of biopolymers and their adsorption at oil/water interfaces favour an increase in the free volume, which is accessible for other macromolecules. Denatura-tion of proteins during food processing decreases their solubility and co-solubility of proteins with one another and with polysaccharides and induces phase separation of the system. 

Tolstoguzov, V.B. (2000). Compositions and phase diagrams for aqueous systems based on proteins and polysaccharides. In H. Walter, D.E. Brooks, and P.A. Srere (Eds.), Micro-compartmentation and Phase Separation in Cytoplasm A Survey of Cell Biology. International Review of Cytology, Vol. 192. Academic Press, San Diego, pp. 3-31. 

Chiral separations can be considered as a special subset of HPLC. The FDA suggests that for drugs developed as a single enantiomer, the stereoisomeric composition should be evaluated in terms of identity and purity [6]. The undesired enantiomer should be treated as a structurally related impurity, and its level should be assessed by an enantioselective means. The interpretation is that methods should be in place that resolve the drug substance from its enantiomer and should have the ability to quantitate the enantiomer at the 0.1% level. Chiral separations can be performed in reversed phase, normal phase, and polar organic phase modes. Chiral stationary phases (CSP) range from small bonded synthetic selectors to large biopolymers. The classes of CSP that are most commonly utilized in the pharmaceutical industry include Pirkle type, crown ether, protein, polysaccharide, and antibiotic phases [7]. 

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