Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2005
Publication Date: 9/1/2005
Citation: Ashby, R.D., Nunez, A., Solaiman, D., Foglia, T.A. 2005. Sophorolipid biosynthesis from the biodiesel co-product stream. Journal of the American Oil Chemists' Society. 82(9):625-630.
Interpretive Summary: Biodiesel is produced from the chemical alteration of animal fats and vegetable oils and is gradually being recognized as an alternate to petro-diesel because of its fuel properties and reduced emissions. Within the next 10 years domestic biodiesel markets are projected to increase from 32 to 350 million gallons. This boost, while favorable for the environment, will result in a large glycerol-rich co-product, the utilization of which must be addressed to help balance the costs of biodiesel synthesis. Glycerol is a large-volume chemical that is commonly used in oral-care products, tobacco, cosmetics and food and beverages. However, in order for glycerol from the biodiesel co-product stream (BCS) to be used in these applications it must be separated from the other components of the BCS, which may be an expensive process. One potential application of the BCS itself is as a feedstock for the microbial synthesis of other value-added products. Sophorolipids (SLs) are synthesized by certain yeasts in large quantities by fermentation. These molecules exhibit properties that permit their use as additives in shampoos, body washes, detergents, cosmetic products and in the lubricant industries. In addition, their unique structure has enlarged interest in their use as a source of specialty chemicals. In this study we successfully produced SLs from intact BCS and were able to exert some control over their chemical structures. This control will facilitate the chemical or enzymatic modification of SLs as we attempt to improve their properties for additional targeted applications. In so doing, we have established an alternative use for BCS and, at the same time, have successfully shown the capacity to manage the structures of SLs.
Technical Abstract: We applied the biodiesel co-product stream (BCS) as a fermentation feedstock for the microbial synthesis of sophorolipids (SLs). The BCS was composed of 40% glycerol, 34% hexane-solubles (made-up of 92% fatty acid soaps / fatty acid methyl esters (FAME) and 6% mono- / diacylglycerols) and 26% water. Batch culture fermentations of the yeast Candida bombicola on pure glycerol resulted in low level synthesis of SLs (~9 g/L). High Performance Liquid Chromatography associated with Atmospheric Pressure Chemical Ionization - Mass Spectrometry (LC/APCI-MS) revealed that the SLs derived from pure glycerol had 99% of the fatty acid 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 fatty acid side-chain) can be chemically modified without the need to first open a lactone ring. 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 utilization of agricultural fats and oils from which the biodiesel was synthesized.