Using yeast killer toxins as bioactive compounds for fermentation control and bioprotection of wine

Killer yeasts secrete proteinaceous toxins with potent antimicrobial activity, offering promising biotechnological applications in winemaking as bioactive substances for fermentation control and wine bioprotection. This review specifically examines current strategies for their use in wine fermentation. Direct application of purified killer toxins can control some spoilage microorganisms under specific oenological conditions, such as low pH and temperature. However, their proteinaceous nature limits stability and efficacy in industrial settings due to variations in parameters such as the turbidity of the grape must or the addition of substances capable of adsorbing and neutralizing these toxins. Despite this, inoculation of must with wine killer yeast strains, which actively grow and secrete toxins during fermentation, is a more robust strategy for this same purpose, particularly in clarified white musts, traditional sparkling wines, and red wines with low wild yeast content. This strategy is more cost-effective and ensures sustained antimicrobial activity throughout the process. Furthermore, when inoculating wine fermentation with mixed cultures of killer and sensitive yeasts, the killer phenotype can enhance yeast autolysis of killer-sensitive dead yeasts during wine aging and contribute to improving the quality of its foamability, roundness, aroma, and flavor. Furthermore, it can also serve as a genetic marker for strain improvement of different yeast species through intraspecific and interspecific hybridization. The continued isolation, characterization, and genetic improvement of novel killer yeasts with enhanced biotechnological traits are essential to expand their industrial applicability in precision enology. Overall, killer yeasts serve as sustainable tools for winemaking, reducing the use of chemical preservatives.