Pullulan production by a non-pigmented strain of Aureobasidium pullulans using batch and fed-batch culture

The production of pigment-free pullulan by Aureobusidium pullulans in batch and fed-batch culture was investigated. Batch culture proved to be a bette r fermentation system for the production of pullulan than the fed-batch cul ture system. A maximum polysaccharide concentration (31.3 g l(-1)), polysac charide productivity (4.5 g l(-1) per day), and sugar utilization (100%) we re obtained in batch culture. In fed-batch culture, feed medium composition influenced the kinetics of fermentation. For fed-batch culture, the highes t values of pullulan concentration (24.5 g l(-1)) and pullulan productivity (3.5 g l(-1) per day) were obtained in culture grown with feeding substrat e containing 50 g l(-1) sucrose and all nutrients. The molecular size of pu llulan showed a decline as fermentation progressed for both fermentation sy stems. At the end of fermentation, the polysaccharide isolated from the fed -batch culture had a slightly higher molecular weight than that of batch cu lture. Structural characterization of pullulan samples (methylation and enz ymic hydrolysis with pullulanase) revealed the presence of mainly alpha-(1 --> 4) ( similar to 66%) and alpha-(1 --> 6) ( similar to 31%) glucosidic l inkages; however, a small amount ( < 3%) of triply linked (1,3,4-, 1,3,6-, 1,2,4- and 1,4,6-Glc p) residues were detected. The molecular homogeneity o f the alcohol-precipitated polysaccharides from the fermentation broths as well as the structural features of pullulan were confirmed by C-13-NMR and pullulanase treatments followed by gel filtration chromatography of the deb ranched digests. (C) 1999 Elsevier Science Ltd. All rights reserved.