Limiting Brettanomyces bruxellensis by early inoculations of Metschnikowia pulcherrima and Oenococcus oeni

Abstract

Metschnikowia pulcherrima (Mp) species has been proposed for several years to wine makers as a bioprotective agent against spoilage organisms (Berbegal et al. 2017). This work studies the association of Mp and Oenococcus oeni strains as an interesting way to limit microbiological alterations associated with Brettanomyces bruxellensis (Bb). In the first part of this study, strains were selected based on their performances. Thus, fast growth, fast consumption of dioxygen and vitamins and strong pulcherriminic acid production were key factors for Mp strains. Selection of O. Oeni was focused on the rate of inoculation, survival and malolactic fermentation (MLF). Finally, B. bruxellensis strains with different sensibility of SO₂ were chosen. The second part of the study aim to monitor the growth of B.bruxellensis during bioprotection phase, alcoholic fermentation (AF), MLF and during post fermentations phase (up to 70 days after inoculations). The impact of the association of one selected Mp strain and 2 selected O. oeni strains on Bb populations is presented here. These fermentations were performed in 1.2 L bioreactors in Cabernet-Sauvignon grape must, at 24 °C. AF and MLF kinetics were monitored by weight loss and L-malic acid concentrations respectively. Bb growth was assessed using plating onto WL agar medium. Moreover, two inoculation times were tested: early co-inoculation (24 hours after Saccharomyces cerevisiae) and late co-inoculation (3/4 of AF). Wines analyses were performed at the end of post fermentation phase: volatile acidity, pH, ethanol, vinylphenols and ethylphenols. AF and FML were completed in 8 and 5 days respectively.  The best results in controlling Bb growth were achieved with the early co-inoculation of Mp and one of the selected O.oeni This association allowed reducing both Bb maximum population and the viable population after 70 days (< 10 CFU/mL). In addition, this resulted in a lower concentration of ethylphenols (10.5 μg/l) compared to control modalities: Bb with only S. cerevisiae(226 μg/L) and Bb with only Mp (169 μg/L). This indicates that mixed cultures of yeasts and lactic acid bacteria could be a new innovative way to control spoilage during the early stage of Bb implantation.

References

Berbegal, G. Spano, M. Fragasso, F. Grieco, P. Russo, V. Capozzi. Appl Microbiol Biotechnol. 2017 Nov 30;102(2):569–576