A rapid method for the evaluation of both extrinsic and intrinsic contamination and resulting spoilage of water‐in‐oil emulsions

Aims: To develop a method for studying the microbial spoilage of water‐in‐oil emulsions and to use this to investigate (i) the intrinsic stability of water‐in‐oil formulations and (ii) Pseudomonas aeruginosa SP1‐induced spoilage of a proprietary emulsion. Methods and Results: Aliquots of test emulsion were placed into wells of a microtitre plate and the opacity (492 nm) monitored at 120‐min intervals over several hours. Cracking of the emulsion was associated with marked reductions in opacity. Rate and extent of change in O.D. could be used as indicators of spoilage. Spoilage of a laboratory emulsion formulation was investigated where microorganisms with demonstrated spoilage potential were incorporated either into the water phase prior to emulsification or where the proportion of contaminated water droplets was varied by dilution of contaminated emulsion with a sterile formulation. Results suggested that the route of introduction was a critical determinant of the probability of gross spoilage. Ps. aeruginosa SP1‐induced spoilage of a proprietary formulation was found to be independent of growth in the formulation; rather it was attributed to the presence of a heat‐labile extracellular spoilage‐factor that was protease labile and possessed both lipase and polysorbate hydrolytic activity. Such spoilage potential was unique to one Ps. aeruginosa culture filtrate amongst five pseudomonads tested. Significance and Impact of the Study: The method is both rapid and reproducible, enables evaluation of the effects of route of contamination upon emulsion spoilage and has potential application in formulation development for cosmetic, pharmaceutical and food products.