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

## TL;DR

This study shows that certain parts of a Torulaspora delbrueckii yeast can help speed up malolactic fermentation in wine, even under tough conditions.

## Contribution

The study identifies specific T. delbrueckii fractions that enhance malolactic fermentation performance in challenging wine environments.

## Key findings

- Inactivated yeast and autolysate fractions from T. delbrueckii improved Oenococcus oeni growth in wine.
- These fractions reduced MLF duration by promoting bacterial viability and mannoprotein consumption.
- T. delbrueckii-derived compounds show potential as enological tools for MLF under restrictive conditions.

## Abstract

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, SO2, 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.