Sophorolipids are surface-active agents which are synthesised by the yeast Candida bombicola. Here we present the possibility of reducing the economical and ecological cost of producing sophorolipids by using waste frying oil as a substrate for C. bombicola. A comparison is made between two grades of biodiesel, waste frying oil and the methyl ester of coco/palm oil as lipophilic substrates on a shakeflask level. Cultivations in a bioreactor using waste frying oil as a substrate were carried out. A new strategy for product recovery without the use of organic solvent is also proposed. The work presented here investigates whether it is possible to produce sophorolipids on waste frying oil and recover the product without using organic solvents.

The naturally occurring sophorolipids synthesized by Candida bombicola possess--despite their overall heterogeneity--little variation in the length of the lipid tail. The range is limited to C16-C18 fatty acids and is governed by the specificity of a cytochrome P450 monooxygenase. However, incorporation of fatty acids differing from the conventional C16-C18 range could broaden up the application potential of sophorolipids. The incorporation of medium-chain fatty acids should render the molecules more hydrophilic and consequently improve their water solubility. Two strategies to circumvent this C16-C18 preference are described in this paper. The first one skips the controlling action of the cytochrome P450 enzyme by supplying the yeast with already hydroxylated substrates, while the other method is based on the deception of the enzyme by presenting it substrates structurally resembling stearic acid. This later strategy can be applied to create very specific tailor-made sophorolipids when combined with post-fermentive modification.

The two last decades have been marked by an increasing environmental awareness. In relationship to detergents, renew-ability, biodegradability, and ecotoxicity have become important issues in the study, development and application of surfactants. In this respect, rapeseed methyl ester ethoxylates are an interesting new class of nonionic surfactants that gain more and more interest on the market. They are easily to formulate into attractive liquid detergents with high cleaning performance and show a more favorable ecotoxicological profile compared to fatty alcohol ethoxylates.

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Sophorolipids are biologically produced surfactants that consist of a hydrophilic sophorose moiety bound to a hydroxylated lipophilic substrate. The highest levels of production are currently achieved using Candida bombicola ATCC 22214, an ascomycotous yeast, as the production organism. The lipophilic moiety is typically found to have a length between C-16 and C-18 and thus the applications of readily produced sophorolipids with regard to cleaning purposes are somewhat limited. Experiments were performed to evaluate the conditions under which a beta-oxidation deficient strain of C. bombicola is able to convert 1-dodecanol into sophorolipids. Both shakeflask and bioreactor cultures yielded C-12, or medium-chained, sophorolipids and the effect of aeration on the production level was investigated and found to favour limited aeration. Analysis of the conversion products was performed through RP-HPLC and the formation of new-to-nature sophorolipids was confirmed by MS. The use of the beta-oxidation deficient strain under limited aeration yielded at least 15 g/L of medium-chained sophorolipids, which is more than in the wild-type strain or when employing full aeration