Abstract :
Effect of post harvest washing as well as cell concentration on de-emulsification characteristics of an isolated Micrococcus species has been tested with Tween 60 – Span 60 stabilised oil in water (o/w) and L-92 pluronic surfactant stabilised water in oil (w/o) model emulsions (kerosene–water). The cells used were 140 h old and grown under submerged conditions at 37°C in a medium containing n-tetradecane (4% v/v) as the carbon source. The harvested bacterial cells when in an unwashed condition (at a cell concentration of 2 mg/ml of emulsion) were found to de-emulsify the o/w system at a much faster rate than the w/o system exhibiting half-life values for the respective system as 10.2 and 127.7 h. Post harvest washing of the cells with any lipid solubilising solvent (n-pentane, n-hexane, kerosene, chloroform–methanol–water (CMW)) yielded a decrease in their de-emulsification power for w/o emulsion. But the decay of o/w emulsion became faster with n-pentane- and kerosene-washed cells as evident from their corresponding half-life values of 3.3 and 4.6 h. Compared to the w/o system, an increase in the concentration of kerosene-washed cell had a direct effect on de-emulsification for the o/w system. For cell concentrations of 2, 3 and 4 mg/ml of the emulsion, the half-life values for the w/o system were 364.8, 442.0 and 454.9 h, respectively. For 2 and 4 mg/ml cell contents, the half-life values for the o/w system were 4.6 and 1.0 h. The decay of both the emulsions was very slow or even incomplete for cell concentrations less than 2 mg/ml. De-emulsifying capacity of the n-tetradecane grown Micrococcus species towards o/w model emulsion improved considerably after washing the cells with n-pentane and kerosene, and use of kerosene-washed cells (4 mg/ml) reduced the half-life to 1 h.
