Microbiological investigations and reply of different preservative systems and the stability of preserved emulsions

The stability of various emulsions containing different preservatives such as methyl paraben, nipa benzyl and lauric acid were studied Three emulsion types (w/o, o/w and w/o/w), prepared with exactly the same composition in order to avoid the influence of the formulation, have been studied. The degree of microbiological activities were tested with respect to Staphylococcus aureus ATCC 6538P, Pseudomonas aeruginosa, Klebsiella pnemonia CCM 2318, Esherichia coli ATCC 11230 and Candida albicans using the Agar Diffusion Cylinder Cup method. The systems were assessed by evaluating several parameters such as the macroscopic aspect, the droplet size and the accelerated stability under centrifugation and various temperatures (4, 25 and 40°C). Conductimetric analysis was used to confirm the types of the emulsions. It was found that the NML preservative mixture (containing methyl paraben, nipa benzyl and lauric acid) was the most effective combination on the test micro-organisms while the w/o/w emulsion system which was preserved with NM (containing nipa benzyl and methyl paraben) was the most stable formulation in stability studies. The reduced stability of emulsions containing NML mixture could be attributed to the insolubility of lauric acid in water