Bioprotection of grape must by Metschnikowia sp.: genericity and mechanism

Abstract

The market trend heads to food products with less chemical inputs, including in oenology. During the winemaking process, sulfites are commonly use to avoid microbiological contamination and stabilization of the wine thanks to its antimicrobial and antioxidant activities. Nevertheless, this use is not without consequences on human health and environment, leading for example to allergic reaction and pollution. A biological alternative to these sulfites has emerges: the bioprotection. This method consists to inoculate at the pre-fermentation stage, a microorganism able to inhibit the growth of the negative indigenous flora. The genus Metschnikowia is well know to have this bioprotection property, especially M. pulcherrima and M. fructicola, but the mechanisms remain poorly studied. This project aims to study the bioprotection abilities of 50 strains of Metschnikowia, including 16 species, against Gluconobacter oxydansand Brettanomyces bruxellensis, both known to lead to defects in organoleptic properties of the wine. To investigate the bioprotection effect, grape juice was inoculated with Metschnikowia sp. and G. oxydans or Metschnikowia sp. And B. bruxellensis. The capacity of Metschnikowia to inhibit G. oxydans growth was evaluated for 7 days by plate counting and by digital PCR for B. bruxellensis. In parallel, Metschnikowia species are inoculated in synthetic grape must to quantify the production of the acid pulcherriminic precursor. This acid is considered as a way for the yeast to compete for iron in the medium, and thus as a method of bioprotection. The results show a diversity in the bioprotection effect towards the spoilage microorganisms and in the production of the acid pulcherriminic precursor. The bioprotection could be an alternative in the sustainable pre-fermentative management of winemaking process.

Acknowledgements: We were grateful to Région Occitanie and INRAE MICA department for funding this project.