Fermentation technologies for the production of exopolysaccharide-synthesizing Lactobacillus rhamnosus concentrated cultures

Claude P. Champagne*
Food Research and Development Center
Agriculture and Agri-Food Canada
3600 Casavant
St. Hyacinthe, QC
J2S 8E3 Canada
Tel:450 773 1105
Fax: 450 773 8461
E-mail: ChampagneC@agr.gc.ca

Nancy J. Gardner
Food Research and Development Center
Agriculture and Agri-Food Canada
3600 Casavant
St. Hyacinthe, QC
J2S 8E3 Canada

Christophe Lacroix
Laboratory of Food Biotechnology
Institute of Food Science and Nutrition
Schmelzbergstrasse 7
ETH Zurich LFV C 20
CH-8092 Zürich, Switzerland

*Corresponding author

Financial support: This work was carried out within the Research Network on Lactic Acid Bacteria, supported by the Natural Sciences and Engineering Research Council of Canada, Agriculture and Agri-food Canada, Novalait Inc., The Dairy Farmers of Canada and Rosell-Lallemand Inc.

Keywords: alginate beads, fed-batch culture, temperature.

The exopolysaccharide (EPS)-producing cultures such as Lactobacillus rhamnosus RW-9595M present a challenge for the culture producers because the high viscosity of the fermented growth medium makes it difficult to recover the cells by centrifugation or filtration. This study examined four approaches to reduce viscosity of the medium while producing high cell densities: incubation temperature, extended incubation in the stationary growth phase, production in alginate gel beads and fed-batch fermentation technology. Automated spectrophotometry (AS) was used to study the effects of temperature, pH and lactate level on growth of the strain. In AS assays, there was no significant difference in final maximal biomass production at temperatures ranging between 34ºC to 44ºC, but lower yields were noted at 46ºC. A pH below 6.0 and a lactate concentration higher than 4% almost completely prevented growth. Under batch fermentation conditions, the viscosity of the medium obtained at 37ºC was two fold higher than for 44ºC. For cultures produced at 37ºC, centrifugation at 10000 g during 5 min did not allow complete recovery of cells, in contrast to cultures grown at 44ºC. An extended period of incubation (5 hrs) in the stationary growth phase did not reduce the final viscosity of the growth medium. For similar biomass levels, the glucose-based fed-batch fermentation allowed a 40% reduction in viscosity of the fermented medium in comparison to traditional batch cultures. High-density cell populations (3 x 10¹⁰ CFU/g) were obtained when L. rhamnosus RW-9595M was grown in alginate beads. However, overall biomass yields in the immobilized cell bioreactor were half of those obtained in free-cell fermentations. Therefore three methods of producing concentrated EPS-producing cultures are proposed.