Assessment of the microbial diversity at the surface of Livarot cheese using culture-dependent and independent approaches

International audienceThe microbial diversity of the surface of a commercial red-smear cheese, Livarot cheese, sold on the retail market was studied using culture-dependent and independent approaches. Forty yeasts and 40 bacteria from the cheese surface were collected, dereplicated using single-strand conformation polymorphism (SSCP) analysis and identified using rRNA gene sequencing for the culture-dependent approach. The cultureindependent approach involved cloning and sequencing of the 16S rRNA gene and SSCP analysis from total DNA extracted from the cheese. The most dominant bacteria were Microbacterium gubbeenense, Leucobacter komagatae and Gram-negative bacteria from the Gamma-Proteobacteria class. Fluorescence in situ hybridization (FISH) analysis was also used to study the cheese microbial diversity with class-level and specific rRNAtargeted probes for bacteria and yeasts, respectively. FISH analysis confirmed that Gamma-Proteobacteria were important microorganisms in this cheese. Four specific FISH probes targeting the dominant yeasts present in the cheese, Candida catenulata, Candida intermedia, Geotrichum spp. and Yarrowia lipolytica, were also designed and evaluated. These probes allowed the detection of these yeasts directly in cheese. The use of the rRNA gene-based approach combined with FISH analysis was useful to investigate the diversity of a surface microbial consortium from cheese

L’illusion de l’or

Au Moyen Âge, les métaux et en particulier l’or, associés dans les peintures murales à certaines couleurs, outre leur rôle iconographique et esthétique, sont porteurs d’une forte charge symbolique en fonction de leur localisation dans l’image. Or, les études récentes de vestiges de dorures dans les peintures murales des édifices religieux ont montré que des feuilles d’étain, à la place d’or, sont identifiées sur la plupart des sites. Une couche de vernis sur la surface de l’étain permettait de lui donner un aspect doré et cette « fausse dorure » était connue de tous les ateliers. Ces techniques sont décrites dans les traités anciens (Théophile, xiie siècle ; Cennini, xive siècle ; Denys, xie siècle). La grande difficulté aujourd’hui est de détecter la présence de ces dorures qui ont disparu lorsque les conditions de conservation ont été défavorables. Grâce à la fluorescence des liants, l’examen sous lumière UV permet de retrouver les zones originellement dorées. Des dorures sur les peintures murales de la chapelle de l’ancien logis abbatial de Moissac (xiie siècle), de l’église de Nogaro (xie siècle) et de la cathédrale de Cahors (xiiie siècle) ont été découvertes (Mounier et al., 2008). L’analyse des prélèvements (stratigraphies, analyses élémentaires par MEB/EDS, des pigments par spectrométrie Raman et les liants par IRTF) réalisés dans ces vestiges de dorure informe sur la technique et les types de métaux utilisés. Pour les historiens d’art, c’est toute une partie de l’interprétation iconographique qui peut être précisée puisque l’application d’une dorure est l’indice d’une hiérarchisation des personnages et/ou d’une volonté de valoriser certains éléments de l’image. Par ailleurs, élargi à l’organisation de l’atelier et la société, l’emploi d’une « fausse dorure » s’explique par des raisons économiques ; autant de facteurs déterminants qui doivent être pris en considération.In the Middle Ages, metals, and gold in particular, associated in wall paintings with certain pigments and colours, in addition to their iconographic and aesthetic function, also had a strong symbolic meaning related to their localization in the image. Recent studies of traces of mediaeval gildings still present in mural paintings have shown that tin leaves, instead of gold, can be identified in most of the sites. A varnish layer allowed giving them a gold aspect. The use of this ‘false gilding’ was common and well-known by workshops. The techniques pertaining to it are described in ancient treatises. Today, the main issue at stake is to detect traces of gildings which have disappeared when conservation conditions were unfavourable. Examination under UV light allows detection of the originally gilded areas. The gildings in the mural paintings of the chapel in the ancient abbey home of Moissac (12th century AD), the paintings in Nogaro Church (11th century), and on the Cahors Cathedral (13th century) have been discovered according to this procedure. The analyses of samples collected from these gildings provide valuable information about the techniques and the types of metals used. The analyses of micro-samples (stratigraphy, SEM/EDXS, Raman spectrometry for the analysis of pigments and FTIR for the binders) show that a gilding or ‘false gilding’, no longer visible today, was often originally applied. For art historians, this allows clarifying part of the iconographic interpretation, as the application of gilding provides information about the hierarchy of the characters and/or the desire to emphasize certain elements of the representation. Moreover, from the point of view of workshop organization, the use of ‘false gilding’ can be related to economic considerations (or supplying facilities)

Microbial interactions in cheese: implications for cheese quality and safety

International audienceThe cheese microbiota, whose community structure evolves through a succession of different microbial groups, plays a central role in cheese-making. The subtleties of cheese character, as well as cheese shelf-life and safety, are largely determined by the composition and evolution of this microbiota. Adjunct and surface-ripening cultures marketed today for smear cheeses are inadequate for adequately mimicking the real diversity encountered in cheese microbiota. The interactions between bacteria and fungi within these communities determine their structure and function. Yeasts play a key role in the establishment of ripening bacteria. The understanding of these interactions offers to enhance cheese flavour formation and to control and/or prevent the growth of pathogens and spoilage microorganisms in cheese

Gilding techniques in mural paintings: three examples in the Romanesque period in France

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L'illusion de l'or - Imitation de dorures dans les peintures murales médiévales

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L’illusion de l’or – Imitation de dorures dans les peintures murales médiévales

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Effects of age and live weight on fat 5α-androstenone levels in young boars fed two planes of nutrition

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Essai de castration immunologique du porc mâle par un vaccin aqueux synthétique

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