Application of oil refinery waste in the biosynthesis of glycolipids by yeast Wlodzimierz Bednarski * , Marek Adamczak, Jan Tomasik, Mariusz Plaszczyk Chair of Food Biotechnology, University of Warmia and Mazury in Olsztyn, J. Heweliusz St. 1, 10-718 Olsztyn, Poland Received 7 July 2003; accepted 27 January 2004 Available online 27 February 2004 Abstract Candida antarctica or Candida apicola synthesized surfactants (glycolipids) in the cultivation medium supplemented with oil refinery waste, either with soapstock (from 5.0% to 12.0% v/v) or post-refinery fatty acids (from 2.0% to 5.0% v/v). The efficiency of glycolipids synthesis was determined by the amount of waste supplemented to the medium and was from 7.3 to 13.4 g/l and from 6.6 to 10.5 g/l in the medium supplemented with soapstock and post-refinery fatty acids, respectively. The studied yeast also synthesized glycolipids in the non-supplemented medium however, by the enrichment of medium with the oil refinery waste, a 7.5–8.5-fold greater concentration of glycolipids was obtained in the post-culture liquid then in the medium without addition of oil refinery waste. The yeast synthesized from 6.6 to 10.3 g dry biomass/l and the intra-cellular fat content was from 16.8% to 30.2%. The efficiency of glycolipids synthesis was determined by yeast species, medium acidity and culture period. The surface tension of the post-culture liquid separated from yeast biomass was reduced to 35.6 mN/m, which corresponded to the surface tension obtained at the critical micelle concentration of glycolipids. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Biosurfactant; Candida apicola; Candida antarctica; Glycolipids; Post-refinery fatty acids; Soapstock 1. Introduction There has been a growing demand for surfactants in the food, pharmaceutical and cosmetic industries and in environmental protection (Bednarski and Adamczak, 1999b). Chemically produced surfactants have increas- ingly been replaced by biotechnologically-based com- pounds through either enzymatic (monoacylglycerols, fatty acid esters of saccharides) (Antczak et al., 1999; Bednarski and Adamczak, 1999a; Bornscheuer, 1995) microbiological (glycolipids) syntheses (Bednarski and Adamczak, 1999b). These biotechnological compounds are primarily synthesized by bacteria or yeast cultured in media with a hydrophobic carbon source such as petro- leum fractions, animal fat or vegetable oil (Hommel, 1990). There have been examples of efficient surfactant synthesis such as sophorolipids by Candida apicola (Hommel and Huse, 1993; Hommel et al., 1994) or mannosylerythritol lipids (MEL) by Candida antarctica. The following are desirable properties of microbiologi- cal surfactants, which determine their increasing de- mand: 1. capacity to reduce surface and inter-phase tension, comparable to chemically produced equivalents, 2. anti-microbial activity towards pathogens, 3. non-toxicity and biodegradability in soil and water, 4. capacity to emulsify, de-emulsify and break froth. Microbiological surfactants are applied for removing contamination from petroleum polluted soil or waters and for washing petroleum storage tanks (Desai and Banat, 1997). In the food industry, biosurfactants can replace the presently used chemically-synthesized sur- face active agents. Besides their purpose of emulsifying and emulsion stabilization, biosurfactants can also play different roles such as retarding bread stalling, anti- oxidation, preventing dusting of powders and reducing friction during product formation. In order to spread the application of microbiological surfactants, methods of possible cost reductions have been sought. Currently, their prices range between 2 and * Corresponding author. Tel.: +48-89-5233687; fax: +48-89-523838. E-mail address: wlodzimierz.bednarski@uwm.edu.pl (W. Bednar- ski). 0960-8524/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2004.01.009 Bioresource Technology 95 (2004) 15–18