Sophorolipid biosynthesis from a biodiesel co-product stream

We applied a biodiesel co-product stream (BCS) as a fermentation feedstock for the microbial synthesis of sophorolipids (SL). The BCS was composed of 40% glycerol, 34% hexane-solubles (made up of 92% FA soaps/FAME and 6% MAG/DAG), and 26% water. Batch culture fermentations of the yeast Candida bombicola on pure glycerol resulted in low-level synthesis of SL (similar to 9 g/L). HPLC associated with atmospheric pressure CI-MS (LC/APCI-MS) revealed that the SL derived from pure glycerol had 99% of the FA side chains linked to the 4 '' hydroxyl group of the sophorose sugar, resulting in a lactonic structure. In contrast, the use of the BCS as feedstock increased the SL yield to 60 g/L and the open-chain form to 75% including both oleic acid and linoleic acid (along with their methyl esters) as the dominant species comprising the side chains. By favoring the open-chain structure, the SL molecules (particularly the FA side chain) can be chemically modified without the need to open a lactone ring first. The ability to use the BCS as a feedstock for SL synthesis will provide an outlet for this residual material, thus helping to stimulate growth in the biodiesel market and the use of agricultural fats and oils from which the biodiesel was synthesized.