F. Youssef et al., Pullulan production by a non-pigmented strain of Aureobasidium pullulans using batch and fed-batch culture, PROCESS BIO, 34(4), 1999, pp. 355-366
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.