Polysaccharides steric forces

In addition to the van der Waals and electrical forces, steric forces resulting from pro-tmding polysaccharide and protein molecules affect interactions specific interactions between charged groups on the cell surface and on the solid surface, hydrogen bonding or the formation of cellular bridges may all occur to complicate the picture. The ten possible forces of interaction between cells and surfaces have been listed as ... 

Already the ancient Egyptians knew that one can keep soot particles dispersed in water when they were incubated with gum arabicum, an exudate from the stems of acaia trees, or egg white. In this way ink was made. The reason for the stabilizing effect is the steric repulsive force cause by adsorbed polymers. In the first case these are a mixture of polysaccharide and plycoprotein, in the second case it is mainly the protein albumin. Steric stabilisation of dispersions is very important in many industrial applications. Direct quantitative measurements were... 

Whatever the mechanism is, particles adhere spontaneously if, at constant temperature and pressure, the Gibbs energy G of the system decreases. The main contributions to the Gibbs energy of particle adhesion A Gad are from electrostatic, hydrophobic and dispersion forces,1 5 and, furthermore, in case of protein adsorption, from rearrangements in the structure of the protein molecule.6 9 When the sorbent surface is not smooth but hairy , additional, mainly steric, interactions come into play.4,10 12 Hairy surfaces are often encountered in nature as a result of adsorbed or grafted natural polymers, such as polysaccharides, that reach out in the surrounding medium with some flexibility. Interaction of particles with such hairy surfaces will be dealt with in section 3. 

Forces between BSM layers preadsorbed on negatively charged mica surfaces have also been reported by Dedi-naite et al. [33]. They also found long-range steric interactions to be predominant, but they did not explore the effect of ionic strength. However, they showed that the anionic surfactant sodium dodecyl sulfate, SDS, has the ability to remove mucin from the surface and that adsorption of chitosan, a cationic polysaccharide, on top of mucin can protect the mucin layer from being removed by the surfactant. 

Emulsions are thermodynamically unstable structures given a degree of kinetic stability by an adsorbed interfacial layer of amphiphilic emulsifiers. The emulsifiers serve to lower the interfacial tension and provide some inter-droplet repulsive forces to stabilize the dispersions (e.g., steric and electrostatic). The interfacial layer is typically between about 1 and lOnm thick for food grade emulsifiers, such as surfactants, phospholipids, proteins, or polysaccharides, and the interfacial concentration is in the order of a few mg per square meter of surface (McClements, 2005 McClements and Decker, 2000). 

The interactions between molecules of polysaccharides and proteins, can be given by covalent bonds, known as conjugated, they form veiy stable structures. There also are physical forces, non-covalent interactions such as electrostatic, hydrophobic, steric, hydrogen bonding, and Van der Waals forces. These interactions are involved in the formation and stabilization of dispersions [80]. 

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