Influence of fermentation time, cryoprotectant and neutralization of cell concentrate on freeze-drying survival, storage stability, and acid and bile exposure of Bifidobacterium animalis ssp. lactis cells produced without milk-based ingredients

AIMS

To investigate the stability of Bifidobacterium animalis ssp. lactis VTT E-012010 (=Bb-12) during freeze-drying, storage and acid and bile exposure. The effect of harvesting time and composition and pH of the cryoprotectant on the survival was evaluated. The procedure was performed by using a milk-free culture medium and cryoprotectants to produce cells for nonmilk-based applications.

METHODS AND RESULTS

Bifidobacterial cells were grown in fermenters in general edible medium for 15 or 22 h. The cell mass was freeze-dried either as non-neutralized or neutralized using sucrose, betaine or reconstituted skim milk (control) as cryoprotectants. For stability studies freeze-dried powders were stored at 37, 5 and -20 degrees C for 2-6 months. In addition, acid and bile tolerance of the powders was tested. Sucrose-formulated B. animalis ssp. lactis preparations had an excellent stability during storage at refrigerated and frozen temperatures for 5-6 months. They also had a good survival during storage at 37 degrees C for 2 months as well as during exposure to pH 3 and 1% bile acids. No difference was observed between 15 and 22 h grown cells or between non-neutralized and neutralized cells. Betaine proved to be a poor cryoprotectant compared with sucrose.

CONCLUSIONS

Fermentation time and neutralization of cell concentrate before freeze-drying had no impact on the storage stability and bile and acid tolerance of freeze-dried bifidobacterial cells. The nonmilk-based production protocol using sucrose as a cryoprotectant yielded powdery preparations with excellent stability in adverse conditions (storage at elevated temperatures and during acid and bile exposure).

SIGNIFICANCE AND IMPACT OF THE STUDY

The results indicate that it is feasible to develop nonmilk-based production technologies for probiotic cultures. This provides new possibilities for the development of nondairy-based probiotic products.

Application of a microplate scale fluorochrome staining assay for the assessment of viability of probiotic preparations

Cell viability in probiotic preparations is traditionally assessed by the plate count technique. Additionally, fluorescent staining combined with epifluorescence microscopy or flow cytometry has been developed for the viability assessment, but the currently available assays are either laborious or require highly sophisticated equipment. The aim of this study was to investigate the applicability of a microplate scale fluorochrome assay for predicting the cell state of freeze-dried Lactobacillus rhamnosus and Bifidobacterium animalis subsp. lactis preparations. In addition to viability assessment with LIVE/DEAD BacLight Bacterial Viability Kit, DiBAC(4)3 stain was used for the kinetic measurement of changes in bifidobacterial cell membrane functions during exposure to low pH. The microplate scale fluorochrome assay results on the viability and cell numbers of probiotic preparations correlated well with the results obtained with the culture-based technique and (with few exceptions) with epifluorescence microscopy. The assay was applicable also for the viability assessment of stressed (acid-treated) cells provided that the cell density in treatments was adjusted to the optimal measurement level of the fluorometer. The microplate scale fluorochrome assay offers a rapid and robust tool for the viability assessment of probiotic preparations, and enables also kinetic measurements.

Malt sprout extract medium for cultivation of Lactobacillus plantarum protective cultures

AIMS

The aim was to develop a cheap cereal-based alternative medium for the large-scale production of biopreservative Lactobacillus plantarum VTT E-79098. We examined the effect of growth medium and pH control on the cell yield of Lact. plantarum E-79098 and the antimicrobial activity of the cell-free extracts.

METHODS

Fermentations using a novel Malt Sprout Extract Medium (MSE) were performed with different pH regimes. The antimicrobial activity of the cell-free extracts against Pantoea agglomerans VTT E-90396 and Fusarium avenaceum VTT D-80147 was assessed with automated turbidometry.

SIGNIFICANCE AND IMPACT OF THE STUDY

When compared with MRS, the MSE medium cultures produced equal growth yields of Lact. plantarum VTT E-79098 and enhanced antimicrobial potential against the Gram-negative bacterium P. agglomerans and a Fusarium fungus. The MSE medium can be used as a low-cost alternative to MRS for producing high cell yields and good antimicrobial activity of Lact. plantarum.

Stationary-phase acid and heat treatments for improvement of the viability of probiotic lactobacilli and bifidobacteria

AIMS

To investigate whether sublethal treatments of stationary-phase probiotic cultures enhance their survival during lethal treatments and to adapt these treatments to the fermenter-scale production of probiotic cultures.

METHODS AND RESULTS

Conditions for acid and heat pretreatments were screened for three Lactobacillus and two Bifidobacterium strains. Strains were sublethally treated both at laboratory scale and at fermenter scale in a strain-specific manner and exposed to a subsequent lethal treatment. At laboratory scale viability improvement was detected in each strain. However, improvement was more pronounced in the Lactobacillus than in the Bifidobacterium strains. At fermenter scale three strains were tested: for the two Lactobacillus strains a marked improvement in viability was obtained whereas for the Bifidobacterium strain the improvement was either minor or not detected.

CONCLUSIONS

Development of treatments for viability enhancement of probiotic strains is feasible, but strain-specific optimization is necessary to obtain notable improvements.

SIGNIFICANCE AND IMPACT OF THE STUDY

Strain-specific treatments were developed for the viability enhancement of stationary-phase probiotic cells both at laboratory and fermenter scale. These results can be utilised in the production of probiotic cultures with improved viability.