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The complex smear microbiota colonizing the surface of red-smear cheese fundamentally impacts the ripening process, appearance and shelf life of cheese. To decipher the prokaryotic composition of the cheese smear microbiome, the surface of a semi-hard surface ripened cheese was studied post-ripening by culture-based and culture-independent molecular approaches. The aim was to detect potential bacterial alterations in the composition of the cheese smear microbiota resulting from cheese storage in vacuum film-prepackaging, which is often accompanied by the development of a surface smear defect. Next-generation sequencing of amplified 16S rRNA gene fragments revealed an unexpected high diversity of a total of 132 different genera from the domains Bacteria and Archaea on the cheese surface. Beside typical smear organisms, our study revealed the presence of several microorganisms so far not associated with cheese, but related to milk, farm and cheese dairy environments. A 16S ribosomal RNA based analysis from total RNA identified the major metabolically active populations in the cheese surface smear as Actinobacteria of the genera Corynebacterium, Brevibacterium, Brachybacterium and Agrococcus. Comparison of data on a higher phylogenetic level revealed distinct differences in the composition of the cheese smear microbiome from the different samples. While the proportions of Proteobacteria and Bacteroidetes were increased in the smear of prepacked samples and in particular in defective smear, staphylococci showed an opposite trend and turned out to be strongly decreased in defective smear. In conclusion, next-generation sequencing of amplified 16S rRNA genes and 16S rRNA from total RNA extracts provided a much deeper insight into the bacterial composition of the cheese smear microbiota. The observed shifts in the microbial composition of samples from defect surface smear suggest that certain members of the Proteobacteria contribute to the observed negative organoleptic properties of the surface smear of cheese after prepacking in plastic foil., AIMS Microbiology, 4 (4)

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International audience; Pigments were extracted from cheese-ripening bacteria belonging to the species Arthrobacter arilaitensis, which plays a role in the colour of cheese. A chromatographic method was applied to characterise the pigment profile. Based on the UVevisible (UVevis) spectra, the mass spectra, and the elution order, eight different carotenoids were identified from the strains. Four of the pigments, namely, all-E-decaprenox-anthin, all-E-sarcinaxanthin, 9-Z-decaprenoxanthin and 15-Z-decaprenoxanthin, which were present as free-form main carotenoids (i.e., non-glycosylated), have been characterised by their UVevis and mass spectra, both in atmospheric-pressure chemical ionisation negative [APCI (À)] and positive modes. The other minor carotenoids, namely, sarcinaxanthin monoglucoside pentaacetate, decaprenoxanthin mon-oglucoside, decaprenoxanthin diglucoside, decaprenoxanthin-C16:0 (decaprenoxanthin-palmitate), present in very low amounts, were only detected in the APCI (À) ionisation mode. Our results provide the first chemical characterisation of the pigments produced by cheese-ripening A. arilaitensis strains, which has not previously been reported.

The microflora on the surface of smear-ripened cheeses is composed of various species of bacteria and yeasts that contribute to the production of the desired organoleptic properties. The objective of the present study was to show that iron availability is a limiting factor in the growth of typical aerobic ripening bacteria in cheese. For that purpose, we investigated the effect of iron or siderophore addition in model cheeses that were coinoculated with a yeast and a ripening bacterium. Both iron and the siderophore desferrioxamine B stimulated the growth of ripening bacteria belonging to the genera Arthrobacter , Corynebacterium , and Brevibacterium . The extent of stimulation was strain dependent, and generally, the effect of desferrioxamine B was greater than that of iron. Measurements of the expression of genes related to the metabolism of iron by Arthrobacter arilaitensis Re117 by real-time reverse transcription-PCR showed that these genes were transcribed during growth in cheese. The addition of desferrioxamine B increased the expression of two genes encoding iron-siderophore ABC transport binding proteins. The addition of iron decreased the expression of siderophore biosynthesis genes and of part of the genes encoding iron-siderophore ABC transport components. It was concluded that iron availability is a limiting factor in the growth of typical cheese surface bacteria. The selection of strains with efficient iron acquisition systems may be useful for the development of defined-strain surface cultures. Furthermore, the importance of iron metabolism in the microbial ecology of cheeses should be investigated since it may result in positive or negative microbial interactions.

Aroma compound production by Proteus vulgaris was studied in a liquid medium under two culture conditions, static or shaken. By using a dynamic headspace technique coupled with gas chromatography-mass spectrometry. 30 volatile components, aldehydes, alcohols, esters, ketones, sulphur compounds and other miscellaneous compounds were identified. P. vulgaris produced a variety of volatile compounds in different amounts, depending on its culture condition. Sensory analysis has shown that the aroma characteristics of each culture condition were clearly differently perceived. The volatile composition was in agreement with the aroma perception. The culture medium obtained without agitation was characterised by a sulphur/rotten egg note and by a high level of H(2)S. The culture medium obtained with agitation was characterised by fruity/fresh and cheese notes and by a high level of alcohols and volatile sulphur compounds. Thus, P. vulgaris could be a useful microorganism to produce various and numerous natural aroma compounds, depending on the culture conditions during fermentation. (C) 2010 Elsevier Ltd. All rights reserved.