Biosurfactant production by free and alginate entrapped cells of Pseudomonas fluorescens

Production of biosurfactant by free and alginate-entrapped cells of Pseudomonas fluorescens Migula 1895-DSMZ was investigated using olive oil as the sole carbon and energy source. Biosurfactant synthesis was followed by measuring surface tension and emulsifying index E24 over 5 days at ambient temperature and at neutral pH. Diffusional limitations in alginate beads affected the kinetics of biosurfactant production when compared to that obtained with free cells culture. Nevertheless, the emulsion stability was improved and fewer by-products interfered with the biosurfactant activity. A decrease in pH down to 5 in the case of immobilized cells was observed during the first 3 days, after which it returned to its initial value. The minimum values of surface tension were 30 and 35 dynes cm(-1) achieved after 40 and 72 h with free and immobilized cells, respectively, while the corresponding maximum E24 values were 67 and 62%, respectively. After separation by acetone precipitation, the biosurfactant showed a rhamnolipid-type in nature, and had a good foaming and emulsifying activities. The critical micellar concentration was found to be 290 mg l(-1). The biosurfactant also showed good stability during exposure to high temperatures (up to 120 degrees C for 15 min), to high salinity (10% NaCl) and to a wide range of pH (4-9).