Improved growth model for two-stage continuous cultures of Lactobacillus helveticus

An unstructured model for growth and lactic acid production during two-stage continuous cultures of Lactobacillus helveticus was previously developed. The Verlhust model was considered to describe growth kinetics. Production models was based on modified Luedeking-Piret expressions involving an inhibitory effect for the first stage (seed culture) and a nutritional limitation effect for the second stage (culture). To account for the decrease of the biomass concentration observed in the second stage, the dilution rate Dc was replaced by an exponential term of the dilution rate (alpha exp (Dc/beta)) in the growth and product relations. Contrarily to the previous model, the important decrease of the biomass concentration observed at steady state in the second stage at high dilution rates, namely close to wash out, was correctly described by the new model. It also proved to satisfactory describes production data and volumetric productivity.

Kinetic analysis and effect of culture medium and coating materials during free and immobilized cell cultures of Bifidobacterium animalis subsp. lactis Bb 12

Microencapsulation technique appears helpful for more protection of Bifidobacteria against acid inhibitory effect. The effect of medium composition and product inhibitory in free cell culture, as well as the effect of the coating materials in immobilized cells, on biomass growth, acid production and substrate utilization kinetics of Bifidobacterium animalis subsp. lactis Bb 12 in uncontrolled batch fermentation was examined. The Monod and the Luedeking and Piret equations with a product inhibition term involving toxic power terms improved model efficiency for both growth and production. The model showed that media and coating materials had an effect on toxic power terms. Cell immobilization had a positive impact on B. animalis culture. Kinetic analysis revealed the permeability of the coating material had a major impact on culture parameters; permeability increased in the following way: Gellan xanthan < Alginate chitosan < K-Carageenan-locust been, and hence growth parameters x m, maximum specific growth rate (h-1) (um) and monod constant (g lactose L-1) (K S) followed the same trend as well as the linking between growth and production. The link between the microbial environment and cell growth was highlighted by the model. It was shown that for an increasing protect effect of coating materials against environmental deleterious factors, namely a decrease of the permeability, transport limitation occurred, which was disadvantageous for cell formation.

Sequential use of ammonium and leucine as nitrogen sources during growth of Geotrichum candidum on a glucose based medium / Uso secuencial del amonio y leucina como fuentes de nitrógeno durante el crecimiento de Geotrichum candidum en un medio basado en glucosa

Geotrichum candidum growth on ammonium and leucine as nitrogen sources and glucose as a carbon source was examined. A clear preference of G. candidum for ammonium over leucine as a nitrogen source was shown. Indeed, ammonium was completely exhausted at the end of exponential growth after less than 35 hrs of culture; in contrast only 5 percent of leucine was concomitantly assimilated. Growth continued at slower rates on glucose and leucine as carbon and nitrogen sources respectively, and at the end of culture (185 hrs), leucine was completely exhausted.