Growth during alcoholic fermentation

Patynowski et al. (2002) showed that yeasts produce an unidentified inhibitory factor (maybe a toxic metabolite) that could be responsible for the inhibition of bacterial growth. These results could explain the antagonism between yeasts and malolactic bacteria, since yeasts are known to produce compounds during alcoholic fermentation such as ethanol, SO2, medium-chain fatty acids and antibacterial proteins/peptides (Weeks et al. 1969 De Oliva et al. 2004 Comitini et al. 2005 Osborne and Edwards 2007). The nature and quantity of peptides and other molecules released by yeasts are different depending on winemaking techniques and the yeast strain. 

In addition to diacetyl, O. oeni produces esters, flavor compounds also important for wine flavor and aroma. Esters are primarily produced by Saccharomyces during alcoholic fermentation (Mason and Dufour, 2000 Nykanen, 1986 Nykanen and Nykanen, 1977 Soles et al., 1982), although evidence shows that esters such as ethyl acetate, ethyl lactate, ethyl hexano-ate, and ethyl octanoate can be synthesized by O. oeni (De Revel et al., 1999 Delaquis-Pascal et al., 2000 Edwards and Peterson, 1994 Maicas et al., 1999 Tracey and Britz, 1989). For example, Edwards and Peterson (1994) reported that strains of O. oeni synthesized relatively large amounts of ethyl lactate (183-1280 /ig/L) during growth in microbiological medium. In agreement, Maicas et al. (1999) reported that 50 mg/L of ethyl lactate was produced in wines fermented with O. oeni, as well as isoamyl acetate and ethyl caproate, compounds important for a pleasant fruity note in wine (Gil et al., 1996 Mason and Dufour, 2000 Nykanen, 1986). 

According to Ciani and Ferraro (1997), the lack of NAD under anero-bic conditions is not restored by glycerol production from dihydroxyace-tone phosphate (Fig. 1.8). In fact, glycolytic pathways are temporarily inhibited in Dekkera/Brettanomyces when these yeasts are introduced into an anaerobic environment (Wijsman et ak, 1984). Because of the lack of NAD, Dekkera/Brettanomyces WAX conduct a limited alcoholic fermentation with the production of primarily ethanol, not acetic acid (Ciani and Ferraro, 1997). Biochemically, another source of NAD during growth of these yeasts in red wines may be the formation of volatile phenols (Section 11.2.2). 

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