Growth prediction of two bacterial populations in co-culture with lactic acid bacteria.

The co-culture growth of Staphylococcus aureus, Escherichia coli and lactic acid bacteria starter culture in milk was quantitatively evaluated and modelled with a set of coupled differential equations originally proposed by Baranyi and Roberts and by Gimenez and Dalgaard (BR-GD model). The lactic acid bacteria starter culture showed the ability to induce an early stationary phase of both E. coli and S. aureus populations at different combination of temperature (ranging from 12 to 37 ℃) and lactic acid bacteria inocula (from approx. 103 to 106 CFU/ml). First, the prediction ability was performed only with parameters estimated from individual growth curves of E. coli, S. aureus and the lactic acid bacteria in milk (Dataset 1, 21 experiments). Subsequently, the model was extended with the average competition coefficients (E-BR-GD model) that represented quantitative relations among the populations. The prediction ability of this model was validated with the second dataset consisting of seven experiments. Results and also their statistical indices (accuracy and bias factors) showed that the E-BR-GD model improved growth prediction of all involved populations. Thus, the total root mean square error decreased from 0.457, 0.840 and 0.322 log CFU/ml (BR-GD model) to 0.290, 0.245 and 0.333 log CFU/ml (E-BR-GD) for S. aureus, E. coli and lactic acid bacteria, respectively. This approach in growth prediction of multiple competing microbial populations can be used in assessment of S. aureus and E. coli exposure from raw milk cheeses consumption and contribute to decision making in prevention of staphylococcal enterotoxin production.

Application of Lactobacillus plantarum in Functional Products Based on Fermented Buckwheat.

In this work, 12 plant-based potential probiotic mashes were produced by fermenting buckwheat with lactic acid cocci of the Fresco DVS 1010 culture and the human-derived isolate Lactobacillus plantarum HM1. The effect of single and coculture fermentation was studied at 30 and 37 ± 0.5 °C for 8 hr (5% CO2 ), followed by a storage period of 21 days (6 ± 0.5 °C). Although milk is the typical growth medium for lactic acid bacteria (LAB), presumably viable counts of Fresco reached levels of 108 to 109 CFU/mL (specific growth rates ranging from 1.07 to 1.40 hr-1 ) with higher counts in coculture fermentation (13%) that differed statistically significantly (P < 0.05). After storage, 194 to 4700 mg/kg lactic acid was found in the mashes, with significantly higher contents after cocultivation (11% to 96%). Based on the overall acceptance of the designed products, milk-based mashes right after the fermentation were evaluated as the most satisfactory (3.3 to 3.6). Those after the storage period (21 days) exhibited an attractive sensory acceptability (2.2 to 3.2).

Physical and bioengineering properties of polyvinyl alcohol lens-shaped particles versus spherical polyelectrolyte complex microcapsules as immobilisation matrices for a whole-cell Baeyer-Villiger monooxygenase.

Direct comparison of key physical and chemical-engineering properties of two representative matrices for multipurpose immobilisations was performed for the first time. Polyvinyl alcohol lens-shaped particles LentiKats® and polyelectrolyte complex microcapsules were characterised by advanced techniques with respect to the size distribution of the particles, their inner morphology as revealed by fluorescent probe staining, mechanical resistance, size-exclusion properties, determination of effective diffusion coefficient and environmental scanning electron microscope imaging. While spherical polyelectrolyte complex microcapsules composed of a rigid semipermeable membrane and a liquid core are almost uniform in shape and size (diameter of 0.82 mm; RSD = 5.6 %), lens-shaped LentiKats® are characterised by wider size distribution (diameter of 3.65 mm; RSD = 10.3 % and height of 0.341 mm; RSD = 32.3 %) and showed the same porous structure throughout their whole volume at the mesoscopic (micrometre) level. Despite differences in their inner structure and surface properties, the pore diameter of ∼ 2.75 nm for regular polyelectrolyte complex microcapsules and ∼ 1.89 nm for LentiKats® were similar. These results were used for mathematical modelling, which provided the estimates of the effective diffusion coefficient of sucrose. This value was 1.67 × 10(-10) m(2) s(-1) for polyelectrolyte complex microcapsules and 0.36 × 10(-10) m(2) s(-1) for LentiKats®. Recombinant cells Escherichia coli-overexpressing enzyme cyclopentanone monooxygenase were immobilised in polyelectrolyte complex microcapsules and LentiKats® for comparison of their operational stability using model Baeyer-Villiger oxidation of (±)-cis-bicyclo [3.2.0] hept-2-en-6-one to regioisomeric lactones as important chiral synthons for potential pharmaceuticals. Both immobilisation matrices rendered high operational stability for whole-cell biocatalyst with no reduction in the biooxidation rate over 18 repeated reaction cycles.

Experimental modelling of thermal inactivation of urease.

Thermal inactivation of jack bean urease (EC 3.5.1.5) was investigated in a 0.1 M phosphate buffer with pH 7. An injection flow calorimetry method was adapted for the measurement of the enzyme activity. The inactivation curves were measured in the temperature range of 55 to 87.5 degrees C. The curves exhibited a biphasic pattern in the whole temperature range and they were well fitted with a biexponential model. A simultaneous fit of all inactivation data was based on kinetic models that were derived from different inactivation mechanisms and comprised the material balances of several enzyme forms and the enthalpy balance characterizing the initial heating period of enzyme solution. The multitemperature evaluation revealed that an adequate model had to incorporate at least three reaction steps. It was concluded that the key reaction steps at urease thermal inactivation were the reversible dissociation/denaturation of native form into an inactive denatured form, and irreversible association reactions of both the denatured and native forms.