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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.

Production of Exopolysaccharide by Lactobacillus rhamnosus R and Analysis of Its Enzymatic Degradation during Prolonged Fermentation

P. L. Pham,1,* I. Dupont,2 D. Roy,1 G. Lapointe,2 and J. Cerning3

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]-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 The decrease in viscosities and molecular weights of EPS withdrawn at different cultivation times permitted us to suspect the presence of a depolymerizing enzyme in the fermentation medium.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 (alpha -D-glucosidase, beta -D-glucosidase, alpha -D-galactosidase, beta -D-galactosidase, beta -D-glucuronidase, and some traces of alpha -L-rhamnosidase). These enzymes were localized, two of them (alpha -D-glucosidase and beta -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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