Submitted to: Biotechnology Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/21/2005
Publication Date: 4/1/2006
Citation: Ashby, R.D., Solaiman, D., Foglia, T.A. 2006. The use of fatty acid-esters to enhance free acid sophorolipid synthesis. Biotechnology Letters. 28:253-260. Interpretive Summary: Sophorolipids (SLs) are molecules that are made up of sugar (water-soluble) and fat (water-insoluble). They are synthesized in large quantities by fermentation of certain yeasts (primarily Candida bombicola) and are nontoxic, biodegradable and reasonably benign for the environment. Because of their unique chemical structures and high yield capacities, they are currently being considered for large scale use in many industries. Their chemical structures cause these molecules to alter the surface tension of water, which imparts surfactant properties to them and allows their use in the detergent and lubricant industries. These molecules are also known to possess emulsifying qualities, which permit their use as additives in many personal care products such as shampoos, body washes and cosmetic products. SLs are naturally produced as structural mixtures, some of which may be fine for one application while others may favor different applications. In order to improve the properties of these molecules for future applications, some chemistry is required, but more chemistry means higher costs and less likelihood that SLs will be conducive to low-cost large-scale applications. One way to cut costs is to make SLs as close to their desired form as possible. In this report, we describe the use of certain soybean oil-derivatives (soyates) along with glycerol (a low cost, large-volume chemical whose production is expected to increase) as fermentation substrates to produce SLs with more controlled chemical structures that are more amenable to chemical alteration. These results will reduce the costs of chemical or enzymatic modification and thus the total cost of using these molecules, ultimately making them more attractive for industrial use.
Technical Abstract: Fatty acid esters were prepared by transesterification of soy oil with methanol (methyl-soyate, Me-Soy), ethanol (ethyl-soyate, Et-Soy) and propanol (propyl-soyate, Pro-Soy) and used with glycerol as fermentation substrates to enhance production of free-acid sophorolipids (SLs). Fed-batch fermentations of Candida bombicola resulted in SL yields of 46 +/- 4 g/L, 42 +/- 7 g/L and 18 +/- 6 g/L from Me-Soy, Et-Soy, and Pro-Soy, respectively. Liquid chromatography with atmospheric pressure ionization mass spectrometry (LC/API-MS) showed that Me-Soy resulted in 71% open-chain SLs with 59% of those molecules remaining esterified at the carboxyl end of the fatty acids. Et-Soy and Pro-Soy resulted in 43% and 80% open-chain free-acid SLs, respectively (containing linoleic acid and oleic acid as the principal fatty acid species linked to the sophorose sugar at the omega-1 position), with no evidence of residual esterification.