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Incompatible: Incorrect shape & size Correct orientation

Incompatible: Correct shape Incorrect size Correct orientation

FIGURE 4.11 The effect of dipolar solutes on the structural organization of water molecules depends on their dimensions and the number and position of their hydrogen bonding groups.

Just as with ionic solutes, the effect of dipolar solutes depends on their concentration. At low solute concentrations, most of the water has the same properties as bulk water, but at high concentrations, a significant proportion of the water has properties which are altered by the presence of the solute. Nevertheless, it takes a greater concentration of a dipolar solute to cause the same effect as an ionic solute because of the greater strength of ion-water interactions compared to dipole-water interactions.

Interactions between dipolar groups and water determine a number of important properties of food components in emulsions. The hydration of the dipolar head groups of surfactant molecules is believed to be partly responsible for their stability to aggregation (Evans and Wennerstrom 1994). When surfactants are heated, the head groups become progressively dehydrated, which eventually causes the molecules to aggregate (Section 4.5). These hydration forces also play an important role in preventing the aggregation of emulsion droplets stabilized by nonionic surfactants (Section 3.8). The three-dimensional conformation and interactions of proteins and polysaccharides are influenced by their ability to form intramolecular and intermolecular hydrogen bonds (Section 4.6). The solubility, partitioning, and volatility of dipolar solutes depend on their molecular compatibility with the surrounding solvent: the stronger the molecular interactions between a solute and its neighbors in a liquid, the greater its solubility and the lower its volatility (Baker 1987).

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