Production of high molecular weight pullulan by Aureobasidium pullulans HP-2001 with soybean pomace as a nitrogen source Hyung-Pil Seo a , Chang-Woo Son a , Chung-Han Chung a , Dae-Il Jung b , Sung-Koo Kim c , Richard A. Gross d , David L. Kaplan e , Jin-Woo Lee a, * a Division of Biotechnology, College of Natural Resources and Life Science, Dong-A University, Hadan-2-dong, Saha gu, Pusan 604-714, South Korea b Department of Chemistry, College of Natural Science, Dong-A University, Pusan 604-714, South Korea c Department of Biotechnology and Bioengineering, College of Fisheries Science, Pukyung National University, Pusan 608-737, South Korea d Department of Chemical Engineering, Polytechnic University, Brooklyn, NY 11201, USA e Biotechnology Center, Department of Chemical Engineering, Tufts University, Medford, MA 02155, USA Received 19 December 2002; accepted 27 February 2003 Available online 2 April 2004 Abstract The production of pullulan by Aureobasidium pullulans HP-2001 was enhanced by yeast extract as a nitrogen source as well as soybean pomace. The highest production of pullulan by A.pullulans HP-2001 with yeast extract was 5.5 g/l whereas that of pullulan with soybean pomace was 7.5 g/l. The gas chromatogram of pullulan produced by A.pullulans HP-2001 with soybean pomace as a nitrogen source showed that the major and minor components were glucose and mannose. The FTIR spectra of pullulans produced with yeast extract, a mixture of yeast extract and soybean pomace, and soybean pomace alone exhibited similar features. The in- crease in content of reducing sugars after pullulanase treatment of pullulans produced with different nitrogen sources indicated that all the pullulans had a-(1,6) glucosidic linkages of a-(1,4) linked maltotriose units. The average molecular weights of pullulans produced with various concentrations of yeast extract and soybean pomace ranged from 0.17 to 1.32 · 10 6 and from 1.32 to 5.66 · 10 6 , respectively. All pullulans produced by A. pullulans HP-2001 in this study had the same basic structures, but their ratios of monomeric components were a little different, which might result in the production of pullulans with different molecular weights. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Aureobasidium pullulans; Pullulan; Yeast extract; Soybean pomace; GC; FTIR; GPC; Molecular weight 1. Introduction Pullulan is an extracellular and unbranched homo- polysaccharide which consists of a-(1 fi 6) linkages of a- (1 fi 4) linked maltotriose units (Bouveng et al., 1963; Catley and Whelan, 1971; Taguchi et al., 1973; Catley et al., 1986). The regular alternation of a-(1,4) and a- (1,6) bonds results in two distinctive properties, struc- tural flexibility and enhanced solubility (Leathers, 1993). Pullulan in relatively low concentration produces high- viscosity solutions and can be utilized to form oxygen- impermeable films (McNeil and Kristiansen, 1990). Films formed from pullulan are suitable for coating foods and pharmaceuticals, especially when exclusion of oxygen is desirable (Yuen, 1974). Pullulan is one of the few neutral water-soluble microbial polysaccharides that can be produced in large quantities by fermentation (Pollock et al., 1992). There are several undesirable features associated with the production of pullulan by Aureobasidium pullulans (Lacroix et al., 1985; Deshpande et al., 1992). These include the inhibitory effects caused by high sugar concentration (more than 5%), decline in the molecu- lar weight of pullulan with the progression of fer- mentation, and the high cost associated with the purification of pullulan from the culture broth (Shin et al., 1987). * Corresponding author. Tel.: +82-51-200-7593; fax: +82-51-200- 6993. E-mail addresses: jwlee@daunet.donga.ac.kr, jwlee@mail.donga. ac.kr (J.-W. Lee). 0960-8524/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2003.02.001 Bioresource Technology 95 (2004) 293–299