Non-Saccharomyces Killer Toxins: Possible Biocontrol agents against Brettanomyces in Wine?

Red wine spoiled by the yeast Brettanomyces bruxellensis is characterised by off-odours commonly
described as horse sweat, phenolic, varnish and band-aid. The growth of this yeast in wine is traditionally
controlled by the use of sulphur dioxide (SO₂). However, the concentration of SO₂, the pH of the wine,
the presence of SO₂-binding chemical compounds in the wine, as well as the strain of B. bruxellensis,
determine the effectiveness of SO₂. Other chemical preservatives have been tested, but are not much more
efficient than SO₂, and methods used to clean barrels are only partially effective. Filtration of wine and
the use of electric currents/fields are also reported to alter the physical and sensory properties of wine. In
this context, alternative methods are currently sought to achieve full control of this yeast in wine. Killer
toxins have recently been proposed to fulfil this purpose. They are antimicrobial compounds secreted
by Saccharomyces and non-Saccharomyces yeasts, displaying killer activity against other yeasts and
filamentous fungi. They are believed to play a role in yeast population dynamics, and this killer phenotype
potentially could be exploited to inhibit the growth of undesired microorganisms within a microbial
ecosystem such as that occurring in wine. In this review, non-Saccharomyces killer toxins are described
and their potential application in inhibiting B. bruxellensis in wine is discussed in comparison to other
tried methods and techniques.