Preservation of solubilized and emulsified systems I: Correlation of mathematically predicted preservative availability with antimicrobial activity.

Mathematical models were investigated for the distribution and antimicrobial activity of chlorocresol in solubilized and emulsified systems stabilized with a nonionic surfactant. The concentration of free preservative in the solubilized systems was described adequately by an equation widely used to describe the binding of small molecules to macromolecules. For the emulsions, this equation was combined with an expression for the partitioning of the preservative between the oil and water phases. It was confirmed that short-term antimicrobial activity can be related to the free (unbound) preservative concentration in the aqueous phase and that preservative solubilized within the surfactant micelles or partitioned into the oil phase does not contribute to short-term preservation.