Abstract
The yeast Lachancea thermotolerans can produce lactic acid during alcoholic fermentation (AF) and thereby acidify wines with insufficient acidity. However, little is known about the impact of L. thermotolerans on Oenococcus oeni, the primary lactic acid bacterium used in malolactic fermentation (MLF). This study explored the impact of sequential cultures of L. thermotolerans and Saccharomyces cerevisiae on MLF performance in white and red wines. Four L. thermotolerans strains were tested in Sauvignon blanc with sequential S. cerevisiae inoculation, compared to an S. cerevisiae control and the initially un-inoculated treatments. The L. thermotolerans wines showed large differences in acidification, and progression of MLF depended on lactic acid production, even at controlled pH. The highest and lowest lactic acid producing strains were tested further in Merlot fermentations with both co-inoculated and sequentially inoculated O. oeni. The low lactic acid producing strain enabled successful MLF, even when this failed in the S. cerevisiae treatment, with dramatically quicker malic acid depletion in O. oeni co-inoculation than in sequential inoculation. In contrast, a high lactic acid producing strain inhibited MLF irrespective of the O. oeni inoculation strategy. In a follow-up experiment, increasing concentrations of exogenously added lactic acid slowed MLF and reduced O. oeni growth across different matrices, with 6 g/L of lactic acid completely inhibiting MLF. The results confirm the inhibitory effect of lactic acid on O. oeni while highlighting the potential of some L. thermotolerans strains to promote MLF and the others to inhibit it.
Highlights
Because of climate change, historic wine regions across the world are warming rapidly (Jones and Davis, 2000; Moriondo et al, 2013)
This paper describes the inhibition of O. oeni by both yeast-derived (Figures 3 and 4) and exogenously added L-lactic acid (Figure 5), which suggests that certain L. thermotolerans modalities could be used to prevent undesired malolactic fermentation (MLF)
This study shows that certain L. thermotolerans modalities can produce sufficient quantities of L-lactic acid to inhibit O. oeni and MLF even in the presence of little or no SO2, thereby offering reduced processing time and preservative use
Summary
Historic wine regions across the world are warming rapidly (Jones and Davis, 2000; Moriondo et al, 2013). Of the non-Saccharomyces yeasts, Lachancea thermotolerans shows great potential for bio‐acidification (Hranilovic et al, 2017) due to its ability to produce L-lactic acid concurrently with alcoholic fermentation (AF). This occurs via lactate dehydrogenase activity from pyruvate obtained through glycolysis (breakdown of sugars) and is an alternative pathway to ethanol production (Hranilovic et al, 2017; Sgouros et al, 2020). L-lactic acid production varies between L. thermotolerans strains, ranging from negligible in some to over 10 g/L in others, the molecular mechanisms of these differences is still under investigation (Hranilovic et al, 2018; Sgouros et al, 2020)
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