The apparent aqueous solubility of diesel oil was determined by
test tube solubilization assay in the presence of increasing concentrations
of biosurfactant (from 0.05 to 2 g/L) as described by Zhu
and Feng (2003). Briefly, aliquots of biosurfactant and 0.2 mL of
diesel were added to a screw-capped tube containing TriseHCl
buffer (20 mM; pH 7.0). For each experiment the hydrocarbon
concentration is 2% and the final volume is 10 mL. Tubes were
capped with plastic closures and incubated in a vertical position for
24 h at 30 C with shaking (150 rpm), in the dark. Residual hydrocarbon
remaining at the surface of the tube was separated
properly and 4 mL were transferred to a clean tube to which 4 mL of
hexane was added prior to extraction by vortexing for 2 min. Then,