Yeast and Filamentous Fungi Microbial Communities in Organic Red Grape Juice: Effect of Vintage, Maturity Stage, SO2, and Bioprotection

Abstract

Changes are currently being made to winemaking processes to reduce chemical inputs [particularly sulfur dioxide (SO2)] and adapt to consumer demand. In this study, yeast growth and fungal diversity were investigated in merlot during the prefermentary stages of a winemaking process without addition of SO2. Different factors were considered, in a two-year study: vintage, maturity level and bioprotection by the adding yeast as an alternative to SO2. The population of the target species was monitored by quantitative-PCR, and yeast and filamentous fungi diversity was determined by 18S rDNA metabarcoding. A gradual decrease of the α-diversity during the maceration process was highlighted. Maturity level played a significant role in yeast and fungal abundance, which was lower at advanced maturity, while vintage had a strong impact on Hanseniaspora spp. population level and abundance. The presence of SO2 altered the abundance of yeast and filamentous fungi, but not their nature. The absence of sulfiting led to an unexpected reduction in diversity compared to the presence of SO2, which might result from the occupation of the niche by certain dominant species, namely Hanseniaspora spp. Inoculation of the grape juice with non-Saccharomyces yeast resulted in a decrease in the abundance of filamentous fungi generally associated with a decline in grape must quality. Lower abundance and niche occupation by bioprotection agents were observed at the overripened stage, thus suggesting that doses applied should be reconsidered at advanced maturity. Our study confirmed the bioprotective role of Metschnikowia pulcherrima and Torulaspora delbrueckii in a context of vinification without sulfites.

Competition for Nitrogen Resources: An Explanation of the Effects of a Bioprotective Strain Metschnikowia pulcherrima on the Growth of Hanseniaspora Genus in Oenology

“…Currently, even in conditions where M. pulcherrima exhibited a bioprotective effect, this efficiency was repressed when inoculated at a lower concentration than the apiculate yeasts. During trials carried out in a cellar, the work of Windholtz et al [ 12 ] demonstrated limited implantation and a loss of efficiency of bioprotective strains in conditions with grapes at advanced maturity compared to grapes at technical maturity which have a lower indigenous flora concentration.…”

“…A wide range of commercial active dry NS yeasts are currently sold by manufacturers as bioprotective yeasts, mainly from Metschnikowia and Torulaspora genera [ 8 ]. The efficiency of bioprotection was previously proven in field trials with a reduction in indigenous yeasts growth through the addition of bioprotection [ 9 , 10 , 11 , 12 , 13 , 14 ], without a thorough investigation of the physiological mechanisms involved. Numerous interactions occur in the microbial world and fall into two main groups: direct (cell–cell contact) or indirect interactions (nutrient competition, toxic compound production, quorum-sensing, enzymatic activity, etc.)…”

Bio-protection in oenology by Metschnikowia pulcherrima: from field results to scientific inquiry

“… Main results on bio-protection obtained in field trials (From data published in journals for professionals and in Chacon-Rodriguez et al, 2020 ; Simonin et al, 2020 , 2022 ; Windholtz et al, 2021a , b,c ; Agarbati et al, 2023 ; Puyo et al, 2023 ). …”

Use of Oenological Tannins to Protect the Colour of Rosé Wine in a Bioprotection Strategy with Metschnikowia pulcherrima

“…The bioprotectants currently proposed to winemakers are non-Saccharomyces yeast strains (most often belonging to the genus Metschnikowia) mainly used as pure cultures [1]. In both red and white winemaking, previous studies have demonstrated that bioprotectant strains colonise the matrix [2][3][4][5]. Their dominance suppresses or limits the development of indigenous yeasts, potential agents of wine spoilage [2][3][4], but remains unsatisfactory to ensure the protection of musts against oxidation.…”