Submitted to: Biotechnology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2008
Publication Date: 2/9/2008
Citation: Ashby, R.D., Solaiman, D., Foglia, T. 2008. Property control of sophorolipids: influence of fatty acid substrate and blending. Biotechnology Letters. 30:1093-1100. Interpretive Summary: Sophorolipids (SLs) are biological-detergent molecules that can be produced in large amounts by fermentation of certain yeasts (primarily Candida bombicola) and are nontoxic, biodegradable and environmentally benign. They are composed of a sugar (water-soluble) component and a fat (water-insoluble) component, which allows them to congregate at interfaces such as between air-water, oil-water or water-solid and alter the properties in those systems. Because of their unique chemical structures and large production capacities, SLs are currently being considered for industrial use primarily in the detergent and personal care product industries. However, in order to broaden the application base for SLs it is necessary to discover new ways of controlling their physical properties. Sophorolipids are naturally produced as structural mixtures, some of which may be beneficial for one application while others may favor different applications. In this study, we used SLs that were derived from different agro-based fat sources (palmitic acid, stearic acid, oleic acid, and linoleic acid) and possessed different structural characteristics to control the surface active (surfactant) properties at air-water and oil-water interfaces without resorting to the use of more costly chemical reactions. By manually mixing the SLs in different ratios the surfactant properties of the SLs were fine-tuned. In this way, a broader application base may be realized for SLs, which can result in a more rapid discovery of new uses for these molecules.
Technical Abstract: Sophorolipids (SLs) were synthesized by fed-batch fermentation of Candida bombicola on glucose and either palmitic acid (SL-p), stearic acid (SL-s), oleic acid (SL-o) or linoleic acid (SL-l) and the structural distribution accurately determined by atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The surfactant properties, including critical micelle concentration (CMC), minimum surface tension (min.ST) and interfacial tension (IFT) were measured by surface tensiometry. Minimum STs of 35-36 mN/m were obtained regardless of the substrate while IFTs ranged from 3-5 mN/m with the exception of SL-l, which had an IFT of 7 mN/m. The largest disparity occurred in the CMC values, which ranged from 35 ppm for SL-s to 250 ppm for SL-l. By manually mixing these four SLs (mentioned above) in different ratios, it was possible to better control the CMC values without affecting the min.ST or IFT, which will prove beneficial as new applications for SLs are established.