Evaluation of Specific Torulaspora delbrueckii Fractions to Stimulate Malolactic Fermentation in Limiting Conditions

Malolactic fermentation (MLF) is a bioprocess driven by lactic acid bacteria (LAB), which is desired in red and highly acidic white wines. Among all LAB, Oenococcus oeni is the main species in wine, followed by Lactiplantibacillus plantarum. The harsh conditions found in wine-not only due to the low nutrient concentration but also the presence of antimicrobial compounds such as ethanol, high acidity, SO_2, and polyphenols-can compromise MLF performance. In recent years, the use of certain non-Saccharomyces yeasts, such as Torulaspora delbrueckii or Metschnikowia pulcherrima, as starter cultures for alcoholic fermentation, has emerged as a promising strategy to improve MLF. In this study, we evaluated the effect of four different fractions from a T. delbrueckii strain on MLF performance. First, the positive impact of this strain as a starter culture on O. oeni growth was confirmed; then, yeast-derived compounds were tested in different wines. Two fractions showed the most promising results in reducing MLF duration: the inactivated yeast fraction and the autolysate fraction. Those enhanced bacterial viability and promoted mannoprotein consumption. These findings highlight the potential of T. delbrueckii-derived compounds as enological tools to support MLF under restrictive wine conditions.