V

Since Vo or O is known from the composition of the emulsion, only P and R need be determined experimentally.

The presence of surfactant micelles alters the native partition coefficient of the preservative molecule because the micellar phase offers an alternative site for preservative molecules (see Fig. 7.21). The partitioning then occurs between the oil globule and the aqueous micellar phases.

For preservatives that are less soluble in the oily phase (P < 1), the concentration in the oily, micellar or aqueous phases increases when the proportion of oil is increased. In contrast, for those preservatives that are more soluble in oil than in water (P > 1), the concentration in all phases decreases when the proportion of the oil phase is increased. This is

Figure 7.21 Diagram showing the equilibrium established between an emulsion globule and a micelle in the continuous phase; the preservative molecule is shown as •.

the case with phenol and chlorocresol (see data given in Table 7.5).

In an emulsion containing 60% arachis oil (O = 1.5) and 1% polysorbate, 9.6% of the phenol but only 0.3% of the more lipophilic chlorocresol is free in the water phase. As much as 93% of the phenol and 99.9% of chlorocresol are locked up in the oily phase or the micellar phases in emulsions containing 10% polysorbate 80.

The use of equation (7.21) can be criticised because of the simple manner in which R has been measured and defined, but the equation is useful to estimate effects of changing parameters. When the emulsified system is very complex, containing not one but at least two emulsifying agents (as most do), the determination of the parameters of the equation is a lengthy process, and a direct experimental approach to the determination of free aqueous concentration, such as a dialysis technique, may be the only approach.

7.3.8 Mass transport in oil-in-water emulsions

Not only preservative molecules partition from the phases in emulsions: drug molecules and flavouring and colouring agents do also. Interest in the extent and rate of flavour release on ingestion of a food emulsion has resulted in quantitative studies of the topic. The model used (see Fig. 7.22) is equally

Table 7.5 Percentage (W) of phenol and chlorocresol partitioned to various sites in arachis oil emulsions0

Arachis oil in water

Phenol

Chlorocresol

Table 7.5 Percentage (W) of phenol and chlorocresol partitioned to various sites in arachis oil emulsions0

Arachis oil in water

Phenol

Chlorocresol

0 0

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