Characterization and extracellular activity of psychrotrophic bacteria isolated from Villalón cheese (fresh variety of Spanish sheep's milk cheese)

Towards an Ecosystem Approach to Cheese Microbiology

Cheese is an ideal environment to serve as a model for the behavior of microbes in complex communities and at the same time allow detailed genetic analysis. Linking organisms, and their genes, to their role in the environment becomes possible in the case of cheese since cheese microbial communities have been "in culture" for thousands of years, with the knowledge of how to grow these organisms passed down by generations of cheesemakers. Recent reviews have described several emerging approaches to link molecular systems biology to ecosystem-scale processes, known as ecosystems biology. These approaches integrate massive datasets now available through high-throughput sequencing technologies with measurements of ecosystem properties. High-throughput datasets uncover the "parts list" (e.g., the species and all the genes within each species) of an ecosystem as well as the molecular basis of interactions within this parts list. Novel computational frameworks make it possible to link species and their interactions to ecosystem properties. Applying these approaches across multiple temporal and spatial scales makes it possible to understand how changes in the parts lists over space and time lead to changes in ecosystems processes. By manipulating the species present within model systems, we can test hypotheses related to the role of microbes in ecosystem function. Due to the tractability of cheese microbial communities, we have the opportunity to use an ecosystems biology approach from the scale of individual microbial cells within a cheese to replicated cheese microbial communities across continents. Using cheese as a model microbial ecosystem can provide a way to answer important questions concerning the form, function, and evolution of microbial communities.

Characterization of the Enterobacteriaceae isolated from an artisanal Italian ewe's cheese (Pecorino Abruzzese)

AIMS

To evaluate some physiological characteristics of the Enterobacteriaceae isolated from Pecorino cheese.

METHODS AND RESULTS

The production of organic acids, secondary volatile compounds, biogenic amines (BA) and the lipolytic and proteolytic activities of Citrobacter braakii, Enterobacter sakazakii, Escherichia coli, Kluyvera spp., Salmonella enterica ssp. arizonae and Serratia odorifera strains were determined in skim milk after 48 h of fermentation at 30 degrees C. The proteolytic activity observed only in Ser. odorifera and Kluyvera spp. was confirmed by the peptide profiles of the pH 4.6-insoluble fraction using RP-HPLC; however, the lipase activity was evidenced in all the isolates of E. coli, Kluyvera spp. and Salm. enterica ssp. arizonae. During fermentation, all the strains utilized citric acid and produced significant quantities of putrescine followed by histamine, spermine and spermidine as well as acetic and lactic acid. Moreover, the major volatile compounds produced were ethanol, 2,3-butanedione, 3-hydroxy-2-butanone, 2-heptanone and acetone.

CONCLUSIONS

The Enterobacteriaceae of dairy origin possess many metabolic activities that could affect the sensory quality of the cheese in which they grow during ripening.

SIGNIFICANCE AND IMPACT OF THE STUDY

The important physiological characteristics possessed by Enterobacteriaceae confirm the complexity of the microbiota of Pecorino Abruzzese cheese, which influences the typical sensory properties of this product.

Caseinolysis in cheese by Enterobacteriaceae strains of dairy origin

AIMS

To study the effect of Enterobacteriaceae strains of dairy origin on caseins under cheese manufacture and ripening conditions.

METHODS AND RESULTS

Strains belonging to the genera Enterobacter, Escherichia, Hafnia and Serratia were isolated from fresh raw milk cheeses. Residual caseins in cheeses made from milk individually inoculated with 10 strains of Enterobacteriaceae were determined by capillary electrophoresis. Hierarchical cluster analysis of strains based on data of residual caseins grouped together strains from the same genus, excepting Hafnia strains, which were separated into two groups. Serratia was the most proteolytic genus in our study. Preferences for degradation of casein fractions differed among the four genera studied.

CONCLUSIONS

Enterobacteriaceae strains posses proteolytic systems active on all casein fractions under cheese manufacture and ripening conditions. The effects on caseins were similar for strains belonging to the same genus.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of Enterobacteriaceae in cheeses may affect proteolysis during ripening. Assays of Enterobacteriaceae proteolytic activity on milk agar plates may underestimate their caseinolytic activity in cheese.