Production of high molecular weight pullulan by Aureobasidium pullulans HP-2001 with soybean pomace as a nitrogen source

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 increase in content of reducing sugars after pullulanase treatment of pullulans produced with different nitrogen sources indicated that all the pullulans had α-(1,6) glucosidic linkages of α-(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.