Sophorolipid production by Candida bombicola: medium composition and culture methods.

Candida bombicola is able to produce sophorolipid molecules with surfactant properties when grown in a medium composed of two different carbon sources (usually sugar and oil) and a nitrogen source (frequently yeast extract). In this work, the composition of the medium and the culture method employed have been studied. The influences of glucose concentration, properties of oil and yeast extract concentration have been taken into account. Accordingly, a production medium composition is proposed (100 g/l glucose, 100 g/l sunflower oil and 1 g/l yeast extract). The most frequent culture methods reported in literature, i.e. batch, medium pulse mode and resting-cell methods, have been tested. The resting-cell method was found to produce the highest final concentration of sophorolipid, obtaining a good yield of carbon sources in a relatively short time. Under the best operational conditions and using the resting-cell method, 120 g/l sophorolipid was obtained in 8 d, with a carbon source yield of 0.60. Product distribution has also been investigated and the sophorolipid molecular structure of opened or cycled molecules has been determined under different operational conditions. Low yeast extract concentration and long fermentation time enhance the production of cycled structures by all the production methods studied.