A practical approach to biosurfactant production using nonaseptic fermentation of mixed cultures

Non‐aseptic production of biosurfactant from molasses by a mixed culture was investigated in stirred batch reactors. Biosurfactant production was quantified by surface tension reduction, critical micelle dilution (CMD), and emulsification capacity (EC). Biosurfactant production was directly correlated with biomass production, and was improved by pH control and addition of yeast extract. Centrifugation of the whole broth increased emulsifying capacity and reduced surface tension. Acidification of the whole broth increased the emulsification capacity but reduced the apparent biosurfactant concentration (CMD), without affecting the surface tension. The emulsification capacity of the cell‐free broth was equivalent to that of a 100 mg/L solution of sodium dodecyl sulfate. The emulsification capacity of the whole broth and cell‐free broth were reduced by about 50% at and above NaCl concentrations of 100mM. Preliminary characterization suggests that the biosurfactant activity is primarily associated with one or more protease‐sensitive species, released from cells in larger quantities after more vigorous centrifugation. © 1994 John Wiley & Sons, Inc.