Brettanomyces yeasts — From spoilage organisms to valuable contributors to industrial fermentations

Abstract

Ever since the introduction of controlled fermentation processes, alcoholic fermentations and Saccharomyces cerevisiae starter cultures proved to be a match made in heaven. The ability of S. cerevisiae to produce and withstand high ethanol concentrations, its pleasant flavour profile and the absence of health-threatening toxin production are only a few of the features that make it the ideal alcoholic fermentation organism. However, in certain conditions or for certain specific fermentation processes, the physiological boundaries of this species limit its applicability. Therefore, there is currently a strong interest in non-Saccharomyces (or non-conventional) yeasts with peculiar features able to replace or accompany S. cerevisiae in specific industrial fermentations. Brettanomyces (teleomorph: Dekkera), with Brettanomyces bruxellensis as the most commonly encountered representative, is such a yeast. Whilst currently mainly considered a spoilage organism responsible for off-flavour production in wine, cider or dairy products, an increasing number of authors report that in some cases, these yeasts can add beneficial (or at least interesting) aromas that increase the flavour complexity of fermented beverages, such as specialty beers. Moreover, its intriguing physiology, with its exceptional stress tolerance and peculiar carbon- and nitrogen metabolism, holds great potential for the production of bioethanol in continuous fermentors. This review summarizes the most notable metabolic features of Brettanomyces, briefly highlights recent insights in its genetic and genomic characteristics and discusses its applications in industrial fermentation processes, such as the production of beer, wine and bioethanol.

Microbial Resources and Innovation in the Wine Production Sector

“…Among others, the yeast Brettanomyces bruxellensis is generally considered one of the main oenological spoilage microbes, since it is able to survive during the winemaking process and confers off-odours to wine (Di Toro et al, 2015;Steensels et al, 2015;Capozzi et al, 2016a). Different B. bruxellensis strains can produce several compounds that are detrimental to the organoleptic quality of wine, including some classes of volatile phenols that derive from the sequential conversion of specific hydroxycinnamic acids such as ferulate and p-coumarate.…”

“…Hydroxycinnamate decarboxylase first transforms these hydroxycinnamic acids into vinylphenols, which are then reduced to 4-ethylphenol and 4-ethylguaiacol respectively by the vinylphenol reductase (Di Toro et al, 2015). Elevated concentrations of 4-ethylphenol are associated with unpleasant aromas described as "stable", "horse sweat" or "leather" (Steensels et al, 2015). To control the proliferation of this yeast, sulphur dioxide is commonly employed, but the efficiency of this chemical compound is subject to wine composition and it can also elicit allergic reactions in humans.…”

Volatile phenols in wine: Control measures of Brettanomyces/Dekkera yeasts

“…Volatile phenols concentration in red wine and its sensory descriptors are presented in Table 1 ( Steensels et al, 2015;Curtin et al, 2005). White wines contain variable quantities of vinyl-phenols but comparing to red wines almost no of ethylphenols.…”

“…The ratio of 4-ethylphenol to 4-ethylguaiacol also varied from wine to wine with reports varying from 3:1 to over 40:1 (Gawel et al, 2004;Steensels et al, 2015). The reason for these differences in wine are still not fully understood, even though they are likely caused by the combined effect of differing ratios between wines p-coumaric and ferulic acids (the precursors of 4-ethylphenol and 4-ethylguaiacol, resp.)…”

“…Traditionally, liquid-liquid extraction methods were employed (Monje et al, 2002;Chatonnet, 1988), but now simpler and more selective extraction methods are applied, such as solid-phase extraction (SPE) (López et al, 2002;Domínguez et al, 2002) solid-phase microextraction (SPME) (Monje et al, 2002;Martorell et al, 2002) or stir bar sorptive extraction (SBSA) (Díez et al, 2004). (Steensels et al, 2015;Curtin et al, 2005) …”