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d. bergmaier, c.p. champagne and c. lacroix. 2004.Aims: Biomass and exopolysaccharide (EPS) production were studied during chemostat cultures in whey permeate medium withLactobacillus rhamnosusRW-9595M-free cells and cells immobilized on solid porous supports (ImmobaSil®).A continuous culture with free cells was conducted for 9 days at dilution rates (D) between 0·3 and 0·8 h−1 in yeast extract (YE)/mineral supplemented whey permeate. Maximum EPS production (1808 mg l−1) and volumetric productivity (542·6 mg l−1 h−1) were obtained for a lowDof 0·3 h−1. A continuous fermentation in a two-stage bioreactor system, composed of a first stage with immobilized cells and a second stage inoculated with free cells produced in the first reactor, was carried out for 32 days. The influence of YE concentration, temperature and dilution rate, and their interactions on biomass, EPS and lactic acid production was investigated. A statistically significant model was found only for lactic acid production. Marked cell morphological and physiological changes led to the formation of very large cell-containing aggregates and a low mean soluble EPS production (138 mg l−1). Aggregate volumetric productivity of the two-stage system varied between 5·7 and 49·5 g l−1 h−1 for different fermentation conditions and times. Aggregates contained a very high biomass concentration, estimated at 74% of aggregate dry weight by nitrogen analysis and 4·3 × 1012 CFU g−1 by a DNA extraction method and a high nonsoluble polysaccharide content (14·2%). At age 24 days, insoluble EPS concentration and volumetric productivity were 1250 mg l−1 and 2240 mg l−1 h−1 respectively. The physiological changes were shown to be reversible when cells were incubated during three successive batch cultures.EPS production and volumetric productivity during continuous free-cell chemostat cultures withL. rhamnosusRW-9595M are among the highest values reported for lactobacilli in literature. Immobilization and continuous culture resulted in low soluble EPS production and large morphological and physiological changes ofL. rhamnosusRW-9595M, with formation of macroscopical aggregates mainly composed of biomass and nonsoluble EPS.This is the first study on continuous EPS production by immobilized LAB. Immobilization and culture time-induced cell aggregation and could be used to produce new synbioticproducts with very high viable cell and EPS concentrations. [ABSTRACT FROM AUTHOR]

d. bergmaier, c.p. champagne and c. lacroix. 2003. Exopolysaccharides (EPS) were produced by Lactobacillus rhamnosus RW-9595M during pH-controlled batch cultures with free cells and repeated-batch cultures with cells immobilized on solid porous supports (ImmobaSil®). Cultures were conducted in supplemented whey permeate (SWP) medium containing 5 or 8% (w/w) whey permeate. For free-cell batch cultures in 8% SWP medium, very high maximum cell counts (1·3 × 1010 CFU ml−1) and EPS production (2350 mg l−1) were measured. A high EPS production (1750 mg l−1) was measured after four cycles for a short incubation period of only 7 h. Several methods for immobilized biomass determination based on analysis of biomass components (proteins, ATP and DNA) were tested. The DNA analysis method proved to be the most appropriate under these circumstances. This method revealed a high maximum immobilized biomass of 8·5 × 1011 CFU ml−1 support during repeated immobilized cell cultures in 5% SWP. The high immobilized biomass increased maximum EPS volumetric productivity (250 mg l−1 h−1 after 7 h culture) compared with free-cell batch cultures (110 mg l−1 h−1 after 18 h culture). High EPS productions were achieved during batch cultures of Lact. rhamnosus RW-9595M in SWP medium, exceeding 1·7 g EPS per litre. Repeated-batch cultures with immobilized cells resulted in increased EPS productivity compared with traditional free-cell cultures. The study clearly shows the high potential of the strain Lact. rhamnosus RW-9595M and immobilized cell technology for production of EPS as a functional food ingredient. [ABSTRACT FROM AUTHOR]