BIOPROTECTION BY ADDING NON-SACCHAROMYCES YEASTS : ADVANCED RESEARCH ON THIS PROMISING ALTERNATIVE TO SO₂

Abstract

Sulphur dioxide has been used for many years for its antimicrobial, antioxidant and antioxydasic properties in winemaking but nowadays, it is a source of controversy. Indeed, consumers are more attentive to the naturalness of their foods and beverages and the legislation is changing to reduce the total SO₂ levels allowed in wines. To limit and replace the doses of sulphur dioxide applied, winemakers can now use bioprotection consisting in live yeast addition as alternative,seems to be promising. This process, lightly used in from the food industry, allows to colonize the environment and limit the development or even eliminate undesirable microorganisms without altering the sensory properties of the product. Recent research took the advantage of the availability of commercial non-Saccharomyces yeast to evaluate their bioprotective potential in oenology. From 2017 to 2021, different experiments were conducted using a mixture of two species (Torulaspora delbrueckii and Metschnikowia pulcherrima) as bioprotection applied at 50 mg/L directly on grapes or musts on different varieties and ripening stages. Our data showed that the bioprotection was successfully implanted in the medium, whith a lower colonization for over-ripened harvests. By using 18S metabarcoding analysis in grape must, we showed that fungal communities such as Hanseniaspora, Aspergillus or Botrytis were significantly less abundant when bio- protection was applied instead of SO₂. Furthermore, bioprotection added in the must rapidly consumed dissolved O₂ and had a negative impact on the strict aerobic acetic acid bacteria by limiting the development of these spoilage microorganisms. Experiments carried out in white must showed that bioprotection also limits the oxidation phenomena: the concentrations of glutathione were significantly higher in bioprotected white musts and final wines. Finally, bioprotection used in red winemaking presents a chemical signature, characterized by fatty acid ethyl esters, increasing the perception of fruitiness in young red wines, but to a lesser extend compared to the same yeast strains in mixed fermentation with S. cerevisiae. After bottling, the bioprotected wines were not sensorially different from wines without SO₂ addition but were different from classical sulphited wines. This research confirm the antimicrobial and a partial protection from oxidation by bioprotection in winemaking and its capacity to preserve sensory properties of wines.