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, <i>Oenococcus oeni</i> is the main species in wine, followed by <i>Lactiplantibacillus plantarum</i>. 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-<i>Saccharomyces</i> yeasts, such as <i>Torulaspora delbrueckii</i> or <i>Metschnikowia pulcherrima</i>, 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 <i>T. delbrueckii</i> strain on MLF performance. First, the positive impact of this strain as a starter culture on <i>O. oeni</i> 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 <i>T. delbrueckii</i>-derived compounds as enological tools to support MLF under restrictive wine conditions.