BIOTECHNOLOGICAL PRODUCTS AND PROCESS ENGINEERING Molasses as fermentation substrate for levan production by Halomonas sp. Faruk Küçükaşik & Hande Kazak & Dilvin Güney & Ilaria Finore & Annarita Poli & Orhan Yenigün & Barbara Nicolaus & Ebru Toksoy Öner Received: 7 October 2010 / Revised: 1 December 2010 / Accepted: 2 December 2010 / Published online: 16 December 2010 # Springer-Verlag 2010 Abstract Levan is a homopolymer of fructose with many outstanding properties like high solubility in oil and water, strong adhesiveness, good biocompatibility, and film- forming ability. However, its industrial use has long been hampered by costly production processes which rely on mesophilic bacteria and plants. Recently, Halomonas sp. AAD6 halophilic bacteria were found to be the only extremophilic species producing levan at high titers in semi-chemical medium containing sucrose, and in this study, pretreated sugar beet molasses and starch molasses were both found to be feasible substitutes for sucrose. Five different pretreatment methods and their combinations were applied to both molasses types. Biomass and levan concentrations reached by the Halomonas sp. AAD6 cells cultivated on 30 g/L of pretreated beet molasses were 6.09 g dry cells/L and 12.4 g/L, respectively. When compared with literature, Halomonas sp. was found to stand out with its exceptionally high levan production yields on available fructose. Molecular characterization and monosaccharide composition studies confirmed levan-type fructan structure of the biopolymers. Rheological properties under different conditions pointed to the typical character- istics of low viscosity and pseudoplastic behaviors of the levan polymers. Moreover, levan polymer produced from molasses showed high biocompatibility and affinity with both cancerous and non-cancerous cell lines. Keywords Levan . Fructan . Halomonas . Molasses . Sugar beet . Exopolysaccharide Introduction The interest in exopolysaccharides (EPSs) has increased considerably in recent years, as they are candidates for many commercial applications in different industrial sectors like food, petroleum, and pharmaceuticals. EPSs have several advantages over chemical equivalents including biocompatibility and biodegradability. In spite of the advantages, fermentation must be cost competitive with chemical synthesis, and many of the potential applications that have been considered for EPSs depend on whether they can be produced economically. Fermentation medium can represent almost 50% of the cost for a microbial fermen- tation (Van Hoek et al. 2003). Employing complex media for growth is not economically attractive because of the high amount of expensive nutrients such as yeast extract, peptone, and salts. Hence to achieve high production yields as well as to compete with synthetic petrochemical products in performance and cost, it is a prerequisite to design an optimal cost-effective production medium. Much effort in fermentation process optimization has been made to produce the biopolymers economically from several inexpen- sive waste substrates, thereby decreasing their production costs (Nicolaus et al. 2010). F. Küçükaşik : O. Yenigün Institute of Environmental Sciences, Boğaziçi University, Istanbul, Turkey H. Kazak : E. T. Öner (*) Department of Bioengineering, Marmara University, Göztepe 34722, Istanbul, Turkey e-mail: ebru.toksoy@marmara.edu.tr D. Güney Department of Biochemistry, Marmara University, Istanbul, Turkey I. Finore : A. Poli : B. Nicolaus Istituto di Chimica Biomolecolare (ICB), CNR, Naples, Italy Appl Microbiol Biotechnol (2011) 89:1729–1740 DOI 10.1007/s00253-010-3055-8