Global survey of the microbial ecosystem during alcoholic fermentation in winemaking

The alcoholic fermentation is a crucial winemaking step. Its failure is problematic. In spite of several studies to understand and elucidate these problems wine global microbial ecology has never been considered. Using conventional microbiological methods and sensitive molecular tools we monitored the alcoholic fermentations of different red grape varieties in several cellars located in Bordeaux area. These observations were made during three successive vintages in different oenological conditions. The effect of the addition of commercial active dried yeast and of initial cold maceration was studied. All these factors were compiled and their effects on microbial changes were investigated. Some of them acted directly on the microbial population of berries surface at the harvest time and should have impact on alcoholic fermentation. They could modify the microbial changes which in some cases could lead to sluggish fermentation. In these cases, we focused on the Brettanomyces bruxellensis spoilage problem. The risk of further contamination was discussed according to the alcoholic fermentation development

Quantification of megastigmatrienone, a potential contributor to tobacco aroma in spirits

A SPME-GC-MS method was adapted and validated in order to quantify 5 megastigmatrienones and related odorous compounds from oak wood: guaiacol, cis-whisky lactone, trans-whisky lactone, gamma-cnonalactone, eugenol, vanillin, and acetovanillone in a single run. The five megastigmatrienone isomers (tabanones) were quantified, for the first time, in Cognac, Armagnac and rum, as contributors to tobacco-like aromas. Spirits aged in oak barrels contain higher amounts, but megastigmatrienones are also present in freshly-distilled spirits. Statistical analysis revealed that freshly-distilled and barrel-aged spirits were differentiated by their megastigma-4,7E, 9-trien-3-one levels. The Armagnac and Cognac samples were distinguished by their concentrations of the megastigma-4,6Z, 8E-trien-3-one isomer. (c) 2016 Elsevier Ltd. All rights reserved

Caractérisation de la composition des sables des dépôts contouritiques dans le Golfe de Cadix durant les périodes interglaciaires des derniers 410ka sous l'influence de la Mediterranean Outflow Water

International audienc

Growth behavior and volatile compound production by Brettanomyces bruxellensis in red wine

Poster n°89 / Thème 2 : Microorganismes du raisin et du vin (Écologie microbienne (identification, interactions). Génomique et dynamique des génomes. Bases moléculaires de l'adaptation à l'environnement. Physiologie et métabolismes des microorganismes d'intérêt œnologique et d'altération des vins, incidence sur la composition et la qualité des vins) Format du poster : A4National audienc

Etude de l'écosystème microbien présent à la surface des barriques utilisées lors de la vinification

National audienceThe microbial community on the surface of wood barrels used in winemaking was determined just before their first use, during first contact with wine, and some months after wine contact during successive racking at different steps of wine elaboration. Five microbial populations (total yeast, non-Saccharomyces yeast, lactic acid bacteria, acetic acid bacteria, and anaerobic and anaerobic tolerant Gram negative bacteria) were identified using 5 different selective culture media. Among each population, species and strains were identified using molecular tools such as the polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis, PCR-restriction fragment length polymorphism and pulsed field gel electrophoresis. At the laboratory scale, the risks of contamination were evaluated by wine inoculation trials and their impact on wine microbial population and chemical properties (volatile phenols and acetic acid) was determined. Before the first use and during the first wine contact, the microbial community on the barrel wood was mainly composed of basidiomycetes (Cryptococcus, Bulleromyces and Rhodotorula) and enterobacteria (Serratia sp. and Shigella sp.). After wine contact, these microorganisms became less and less detectable, which could be explained by their low ethanol resistance. However, some species could resist ethanol and remain detectable some weeks after the first barrelling. The ability of these species to degrade some wood components could affect the wine microbial consortium. In addition, since the first racking, the majority of microbial species found on the wood barrel surface was composed of major wine yeast (Saccharomyces cerevisiae) and bacterial (Oenococcus oeni) species, as well as spoilage organisms such as Brettanomyces bruxellensis, Pediococcus parvulus and Gluconobacter oxydans. Laboratory trials of contamination suggested that these residual populations were unable to cause wine alteration such as volatile phenol and acetic acid production. The microorganisms present on the wood surface could not modify the microbial steady state of wine containing some populations regulated by oenological practices (sulfating, racking) and also by microbial interactions between each species. When the microbial population was low as in the case after filtration or heat treatment, the contamination was more possible. In any cases, washing of barrels at each racking is strongly recommended to progressively eliminate the microorganisms that are adhered to the wood and to obtain an efficient microbial stability of the wine

Debaryomyces hansenii, Proteus vulgaris, Psychrobacter sp and Microbacterium foliorum are able to produce biogenic amines

The occurrence of biogenic amines (BAs) produced by the microbiota of fermented foods is a source of health concern. The three bacteria Microbacterium foliorum, Proteus vulgaris and Psychrobacter sp. and the yeast Debaryomyces hansenii, isolated from surface-ripened cheeses, are known to contribute to their aromatic properties. The potential of each of these strains to produce BAs was investigated, both in pure cultures of each bacterium in a laboratory medium supplemented with amino acids and in mixed cultures with D. hansenii in a model cheese during the ripening process. BAs were quantified using HPLC. In the laboratory medium, all microbial strains produced at least one biogenic amine. P. vulgaris produced the highest amount of BAs, mainly putrescine and isoamylamine, with a total of 195 mg.L-1. In all of the model cheeses, the highest levels of BAs were determined at the end of ripening. With D. hansenii and M. foliorum, the total levels of BAs were below 10 mg.kg(-1) of cheese. Gram-negative bacteria, in association with D. hansenii, produced up to 25 mg.kg(-1) of BAs. Histamine was produced when Psychrobacter sp. was present, and isoamylamine, when P. vulgaris was present in the cheese ecosystem. Though these strains are able to catabolise amino acids into flavour compounds, they are also able to produce BAs, particularly putrescine, isoamylamine and histamine, showing the simultaneous expression of the two catabolic pathways. This study is a preliminary work on the assessment of the impact of all ripening microorganisms on the sanitary quality of cheese

Sensory and analytical re-evaluation of “Brett character”

International audienceWorldwide wine production has been significantly affected by Brettanomyces bruxellensis spoilage. This alteration, sometimes referred to as “Brett character”, results in the production of several volatile compounds and a large spectrum of flavours and aromas. Ethylphenols (namely 4-ethylphenol and 4-ethylguaiacol) are the best-known markers of this defect with a commonly used aggregate detection threshold of about 400 μg/l. Fifty-one Bordeaux red wines were tasted with the aim of wine profiling for commercial purposes. Ethylphenol concentrations of wines were very poorly correlated to the corresponding tasting notes. Sensory analysis was employed to demonstrate the complexity of “Brett character”. A masking effect of isobutyric acid and isovaleric acid on the detection of ethylphenols in wine was proven. This partly explained the poor correspondence between ethylphenol concentrations and presence of “Bretty” descriptors