Yeast Extract Lactate Research Articles

One-Year Monitoring of Prevalence and Diversity of Dairy Propionic Acid Bacteria in Raw Milk by Means of Culture-Dependent and Culture-Independent Methods.

Even low levels of dairy propionic acid bacteria (dPAB) can cause cheese defects, resulting in severe economic losses for the producers of selected raw milk cheeses. Therefore, routine quality control of raw cheese milk for dPAB contamination is essential if propionic acid fermentation is undesired. Although knowledge of dPAB contamination of raw milk is important to understand cheese spoilage, long-term dPAB screening data are outdated, and studies taking into account different farm management parameters and their potential influence on dPAB levels are scarce. This study aims to provide insight into the dPAB levels of raw milk over time, to identify farm management factors that potentially influence dPAB levels, and to compare a cultural yeast extract lactate agar (YELA) and lithium glycerol agar (LGA) and a culture-independent method (qPCR) for dPAB quantification with respect to their applicability in routine quality control for the dairy industry. For this purpose, bulk tank milk from 25 dairy farms was screened for dPAB contamination over a one-year period. We were able to identify significant differences in the dPAB contamination levels in raw milk depending on selected farm-specific factors and observed relationships between the different types of milking systems and dPAB contamination levels in raw milk. When dPAB were quantified by cultivation on YELA, strong overgrowth of commensal microbiota impeded counting. Therefore, we conclude that quantification on LGA or by qPCR is preferable. Both methods, colony counting on LGA as well as quantification of dPAB using qPCR, have advantages for the application in (routine) quality control of raw milk, one being low-tech and inexpensive, the other being fast and highly specific, but the detection of (low level) dPAB contamination in raw milk remains a challenge.

Different culture media and purification methods unveil the core proteome of Propionibacterium freudenreichii-derived extracellular vesicles.

Bacterial extracellular vesicles (EVs) are natural lipidic nanoparticles implicated in intercellular communication. Although EV research focused mainly on pathogens, the interest in probiotic-derived EVs is now rising. One example is Propionibacterium freudenreichii, which produces EVs with anti-inflammatory effects on human epithelial cells. Our previous study with P. freudenreichii showed that EVs purified by size exclusion chromatography (SEC) displayed variations in protein content according to bacterial growth conditions. Considering these content variations, we hypothesized that a comparative proteomic analysis of EVs recovered in different conditions would elucidate whether a representative vesicular proteome existed, possibly providing a robust proteome dataset for further analysis. Therefore, P. freudenreichii was grown in two culture media, and EVs were purified by sucrose density gradient ultracentrifugation (UC). Microscopic and size characterization confirmed EV purification, while shotgun proteomics unveiled that they carried a diverse set of proteins. A comparative analysis of the protein content of UC- and SEC-derived EVs, isolated from cultures either in UF (cow milk ultrafiltrate medium) or YEL (laboratory yeast extract lactate medium), showed that EVs from all these conditions shared 308 proteins. This EV core proteome was notably enriched in proteins related to immunomodulation. Moreover, it showed distinctive features, including highly interacting proteins, compositional biases for some specific amino acids, and other biochemical parameters. Overall, this work broadens the toolset for the purification of P. freudenreichii-derived EVs, identifies a representative vesicular proteome, and enumerates conserved features in vesicular proteins. These results hold the potential for providing candidate biomarkers of purification quality, and insights into the mechanisms of EV biogenesis and cargo sorting.

Adaptation of Propionibacterium freudenreichii to long-term survival under gradual nutritional shortage.

Background Propionibacterium freudenreichii is an Actinobacterium widely used in the dairy industry as a ripening culture for Swiss-type cheeses, for vitamin B12 production and some strains display probiotic properties. It is reportedly a hardy bacterium, able to survive the cheese-making process and digestive stresses.ResultsDuring this study, P. freudenreichii CIRM-BIA 138 (alias ITG P9), which has a generation time of five hours in Yeast Extract Lactate medium at 30 °C under microaerophilic conditions, was incubated for 11 days (9 days after entry into stationary phase) in a culture medium, without any adjunct during the incubation. The carbon and free amino acids sources available in the medium, and the organic acids produced by the strain, were monitored throughout growth and survival. Although lactate (the preferred carbon source for P. freudenreichii) was exhausted three days after inoculation, the strain sustained a high population level of 9.3 log10 CFU/mL. Its physiological adaptation was investigated by RNA-seq analysis and revealed a complete disruption of metabolism at the entry into stationary phase as compared to exponential phase.Conclusions P. freudenreichii adapts its metabolism during entry into stationary phase by down-regulating oxidative phosphorylation, glycolysis, and the Wood-Werkman cycle by exploiting new nitrogen (glutamate, glycine, alanine) sources, by down-regulating the transcription, translation and secretion of protein. Utilization of polyphosphates was suggested.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3367-x) contains supplementary material, which is available to authorized users.

Research on Some Factors Influencing Acid and Exopolysaccharide Produced by Dairy Propionibacterium Strains Isolated from Traditional Homemade Turkish Cheeses

In this study, a total of 32 isolated strains and 5 reference strains of dairy propionibacteria were analyzed for acid and exopolysaccharide (EPS) production in skim milk and yeast extract-lactate broth (YEL) media in order to investigate the physiological background and preservative role of acid and EPS. The effects of final culture pH and optical density on acid and EPS production were also determined. On average, all strains produced more acid and reached lower final pH values in skim milk than in YEL medium. While the correlations obtained between the acid produced by propionibacterium strains and their final culture pH in skim milk medium were significant (P < 0.01), no correlations were found between optical density, final pH, and produced acid in YEL medium. Sixteen isolated and five reference strains of propionibacteria were tested further for the ability to produce propionic and acetic acids. On average, Propionibacterium freudenreichii subsp. shermanii and P. freudenreichii subsp. freudenreichii strains produced higher amounts of propionic and acetic acids than did Propionibacterium jensenii in YEL medium. The acid produced by these strains may be used as a preservative in the food industry for replacement or reduction of the increasing use of chemical additives. The EPS production by propionibacterium strains during growth in YEL medium was 72 to 168 mg/liter, while in skim milk it was 94 to 359 mg/liter. The monomer compositions of the EPSs formed by the six selected dairy propionibacteria strains were analyzed. The EPSs may have applications as food grade additives and viscosity-stabilizing agents.

Extracellular polymer production and potential for aggregate formation by classical propionibacteria

Nineteen Propionibacterium strains were screened for extracellular polymer (ECP) production. The best producer, P. jensenii S1, was introduced into two different media, Yeast Extract Lactate (YEL)-medium and Apricot Effluent (AE)-medium. The YEL medium samples were incubated in different mixing systems (a roller-table and a linear shaking platform) for 24 days at 35 °C. According to the volatile fatty acids and pH profiles, no real differences could be detected between the two mixing systems. Bacterial aggregates were, however, only observed in the roller-table samples. The process was repeated with AE-medium on the roller-table. Larger and more stable flocs were observed in the AE-medium samples. Scanning electron microscopy and PCR analysis confirmed the presence of propionibacteria in these flocs even after 5 months of storage at 4 °C. It was concluded that ECP-producing Propionibacterium strains could be manipulated to form bacterial flocs under certain environmental conditions, which might be enhanced in the presence of fibrous material occurring naturally in food industry effluents.

Optimized standard conditions for determination of nitrate reduction in propionibacteria

Nitrate reduction is currently considered to be a key characteristic for the determi- native grouping of strains of the Propionibacterium but many controversies exist regarding nitrate reduction by members of this genus. The aim was thus to determine the influence of dif- ferent media, nitrate concentrations and pH values under aerobie and anoxie conditions, using the conventional technique and the diazotization coupling method, on the nitrate reducing capability of propionibacteria. The low concentrations of nitrite formed during nitrate reduction by the propionibacteria could not be accurately determined using the conventional technique. This method was found to be reliable only when the initial KN03 concentration exceeded 1.0 mmol/L. ln contrast, with high concentrations of nitrite, the diazotization coupling method was found to be too sensitive. Nitrate reduction in the yeast extract lactate (Y EL) medium with added glu- cose and KN03, was not effective as only low concentrations of nitrite were produced. Good nitrate reduction was obtained on both the YEL and yeast extract (YE) media with or without the addi- tion of KN03 (pH 8.0) to the test media. The presence of nitrite in the YEL culture media of the five Propionibacterium type strains, un der aerobie conditions (pH 8.0) with 20 mmol/L KN03, was determined using the diazotization coupling method. The type strains of P. acidipropionici, P. acnes and P.freudenreichii subsp.freudenreichii were able to reduce nitrate. In contrast, the P. jensenii and P. thoenii type strains were not able to reduce nitrate under these conditions. Furthermore, P. acidipropionici and P. acnes were both able to further reduce the formed nitrite to gaseous nitrogen. It was found that nitrate reduction was strongly influenced by environmental factors such as oxygen, nitrate concentration, pH, media composition, incubation period and the presence of glucose. Data are presented which permit a more standardized determination of nitrate reduction of propionibacteria. © Inra/Elsevier, Paris.

Enumeration of propionibacteria in raw milk using a new selective medium

Summary - Prapionibacteria were enumerated using a new medium in 202 raw milk samples taken from tanker lorries, collected over a 1-year period fram 9 regions of France. This medium, called Pal Propiobac, has been compared with yeast extract lactate agar (YELA) for its efficiency to enumerate propionibacteria in 29 of these milk samples. Prapionibacteria counts were of the same order of magnitude on both media. However, total counts on YELA (reflecting ail the milk flora able to graw on the medium) were markedly higher than total counts on Pal Propiobac, which shows a higher selectivity of the latter medium towards milk microorganisms other than propionibacteria. Moreover, more than onequarter (8 of 29) of the milk samples could not have been enumerated on YELA because of the lack of colonies of typical appearance on this medium. Prapionibacteria counts in raw milk ranged between less than 10 cfu/ml to 1.3 104 cfu/ml. The variations observed for milk samples collected the same day in a given region were of the same order of magnitude as variations depending on regional or seasonal factors. The geometric mean of propionibacteria counts of ail the tested samples was 2.19 log cfu/ml, with a standard deviation of 0.58. The significance of the propionibacteria content of milk for cheese technology is discussed.