Diesel solubilization assays
Test tube solubilization assay
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,