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Applied and Environmental Microbiology, July 1999, p. 2863-2870, Vol. 65, No. 7
Division of Industrial Microbiology,
Fermentation Technology and Downstream Processing (IMDO),
Department of Applied Biological Sciences, Vrije Universiteit Brussel,
B-1050 Brussels, Belgium
Received 2 November 1998/Accepted 1 April 1999
Streptococcus thermophilus LY03 is a yogurt strain
producing the same exopolysaccharide material in both milk and MRS
broth. Actually, two types of exopolysaccharides are produced
simultaneously. The two exopolysaccharides are identical in monomer
composition (galactose and glucose in a 4:1 ratio) but differ in
molecular size. Gel permeation chromatography revealed a
high-molecular-mass exopolysaccharide (1.8 × 106)
and a low-molecular-mass exopolysaccharide
(4.1 × 105). Both exopolysaccharides can be isolated
from the fermentation broth separately. The proportion in which they
are produced is strongly dependent on the carbon/nitrogen ratio of the
fermentation broth. A shift from a high-molecular-mass
exopolysaccharide to a low-molecular-mass exopolysaccharide
was observed with increasing initial complex nitrogen concentrations.
All necessary biokinetic parameters to study the kinetics of S. thermophilus LY03 fermentations were obtained from a
mathematical model which describes both S. thermophilus LY03 growth and exopolysaccharide production and degradation. The model is valid with various initial
complex nitrogen concentrations and can be applied to simulate
exopolysaccharide production in a milk medium.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Indication that the Nitrogen Source Influences Both Amount and
Size of Exopolysaccharides Produced by Streptococcus
thermophilus LY03 and Modelling of the Bacterial Growth and
Exopolysaccharide Production in a Complex Medium
*
Corresponding author. Mailing address: Division of
Industrial Microbiology, Fermentation Technology, and Downstream
Processing (IMDO), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium. Phone: 32-2-6293612. Fax: 32-2-6292720. E-mail: ldvuyst{at}vub.ac.be.
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