Measurement of emulsification activity
The emulsification activity of biosurfactant An6 towards diesel
was measured according to the method of Cooper and Goldenberg
(1987) with a slight modification. Briefly, 4 mL of diesel oil was
mixed, for 2 min, with 4 mL of biosurfactant An6 (5 g/L), SDS or
Tween 80, and subsequently incubated at 20 C for 24 h. The
emulsification index (EI) was calculated according to the following
formula:
EI ¼ He
Ht 100
where He and Ht are the heights of emulsion and total height of the
mixture, respectively. All measurements were performed in
triplicate.
To investigate thermal stability, the biosurfactant solution was
incubated in water bath at different temperatures (from 20 to
100 C) for 15 min, After cooling the treated samples to room
temperature, the emulsification index (EI) was calculated. The effect
of pH on biosurfactant activity was examined by assaying
emulsifying activity after incubation for 1 h at 4 C in the pH range
of 3.0e10.0. Values presented are the mean of triplicate analyses.
Di