BACKGROUNDThis study deals with the large-scale production of biosurfactant from soybean oil soapstock by Pseudomonas aeruginosaMR01. The production of biosurfactant was carried out in a newly designed bioreactor equipped with recycling flow under three operational conditions. Kinetic studies were conducted at both shake flask and 5-L bioreactor scales during fermentation in a soapstock medium. Mathematical equations were developed to model the kinetic patterns at both scales. RESULTStatistical analyses demonstrated the goodness of fit, with regression r-squared, R-2, between 0.97and 0.99 for different models. Furthermore, biosurfactant concentration in the bioreactor including the recycling flow, which was switched on and off during a 6-h period, reached 25.5 g L-1 (Y-P/S=0.9) which showed 41.5% and 21.5% growth compared with experiments conducted in a shake flask and a non-recycling-flow bioreactor, respectively. Moreover, the crude biosurfactant at a concentration of 24 mg L-1 was observed to have lowered the surface tension of double-distilled water from 72 mN m(-1) to 28.5 mN m(-1) and displayed an emulsification index (E24) of 63% against kerosene. CONCLUSIONThe results showed the recycling-flow bioreactor to be a feasible model for further large-scale studies of biosurfactants. (c) 2015 Society of Chemical Industry