for 20 min.
Rhamnolipid was then precipitated by acidification of the
supematant to pH 2.0 and centrifugation at 12,100 x g for 20
min. The precipitate was dissolved in 0.05 M bicarbonate
(8.6), reacidified, and recentrifuged at 12,100 x g for 20 min.
Following centrifugation, the precipitate was extracted with
chloroform-ethanol (2:1) three times. The organic solvent
was evaporated on a rotary evaporator, and the yellowish
oily residue was dissolved in 0.05 M bicarbonate (pH 8.6).
The biosurfactant concentration was then estimated independently
by surface tension measurement and by L-rhamnose
measurement.