Résumé
Nowadays, the trend is to reduce the use of chemical inputs in the food sector, including in oenology. One of the inputs widely used in the wine making process are sulfites, for its several properties: antimicrobial and antioxidiant. This use isn’t without consequences on consumer’s health and environment, it can lead for example to allergic reactions and pollution. To limit the addition of chemical inputs, microbial alternatives are used. It consists to inoculate in grape must, a micro-organism able to inhibit the growth of the negative indigenous flora during the phase before the fermentation and to guarantee the sensory qualities of wines. One of the specie the most used for its bio-protection capacity is the genus Metschnikowia. This project aims to study the phenotypical diversity in wine fermentative conditions and the diversity of bio-protector character of Metschnikowia sp. To study the phenotypical diversity, 16 species of Metschnikowia within 50 strains have been selected depending their localization, their origins, and the species. These strains are used to ferment grape synthetical must, and the products of carbon central metabolism are analyzed by HPLC and the production of volatile molecules by GC-MS. In parallel, these strains are put in co-culture, with an acetic bacterium (Gluconobacter oxydans), known to lead to acetic souring, in commercial grape juice to study the interaction between yeast at 106cell/mL, and bacteria at 103cell/mL. Their growth is followed at day 0, 1, 2 and 7 through drop test on selective medium. Similar to the fermentation aspects, the volatile profiles of the different strains were quite different, which corroborated the diversity of the Metschnikowia yeasts. The results of the drop test show an effect of bio-protection from the species Metschnikowia on the growth of G. oxydans. This work can underline both the potential of Metschnikowia yeast strains for inhibiting spoilage wine microorganisms and increasing aroma compounds.