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Applied and Environmental Microbiology, June 2000, p. 2302-2310, Vol. 66, No. 6
Food Research and Development Centre,
Agriculture Canada, Saint-Hyacinthe, Québec, J2S 8E3,
Canada1; Dairy Research Centre,
Université Laval, Québec, Canada2;
and Station de Recherches Laitières, Institut
National de la Recherche Agronomique, 78352 Jouy-en-Josas Cedex,
France3
Received 11 November 1999/Accepted 15 March 2000
The potential of Lactobacillus rhamnosus R for
producing exopolysaccharide (EPS) when grown on basal minimum medium
supplemented with glucose or lactose was investigated. EPS production
by L. rhamnosus R is partially growth
associated and about 500 mg of EPS per liter was synthesized with both
sugars. The product yield coefficient (YEPS/S)
was 3.15 (0.0315 g of EPS [g of lactose]
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Production of Exopolysaccharide by Lactobacillus
rhamnosus R and Analysis of Its Enzymatic Degradation
during Prolonged Fermentation
1) and 2.88 (0.0288 g of EPS [g of glucose]1). It was clearly shown
that the amount of EPS produced declined upon prolonged fermentation.
Degradation of EPS in fermentation processes was also assessed by
measuring its molecular weights and viscosities. As these reductions
might have a negative effect on the yield and viscosifying properties
of EPS, it was essential to examine possible causes related to this
breakdown. The decrease in viscosities and molecular weights of EPS
withdrawn at different cultivation times permitted us to suspect the
presence of a depolymerizing enzyme in the fermentation medium. Our
study on enzymatic production profiles showed a large spectrum of
glycohydrolases (
-D-glucosidase, 
-D-glucosidase, -D-galactosidase,
-D-galactosidase, -D-glucuronidase, and
some traces of -L-rhamnosidase). These enzymes were
localized, two of them (-D-glucosidase and
-D-glucuronidase) were partially purified and
characterized. When incubated with EPS, these enzymes were capable of
lowering the viscosity of the polymer as well as liberating some
reducing sugars. Upon prolonged incubation (27 h), the loss of
viscosity was increased up to 33%.
*
Corresponding author. Mailing address: Food Research
and Development Centre, Agriculture Canada, 3600, Casavant Blvd. West, Saint Hyacinthe, Quebec J2S 8E3, Canada. Phone: 1-450-773-1105. Fax:
1-450-773-8461. E-mail: phampl{at}em.agr.ca.
Applied and Environmental Microbiology, June 2000, p. 2302-2310, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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