Untitled

Abstract

The effect of killer strains of Saccharomyces cerevisiae on the growth of sensitive strains during must fermentation was studied by using a new method to monitor yeast populations. The capability of killer yeast strains to eliminate sensitive strains depends on the initial proportion of killer yeasts, the susceptibility of sensitive strains, and the treatment of the must. In sterile filtered must, an initial proportion of 2-6% of killer yeasts was responsible for protracted fermentation and suppression of isogenic sensitive strains. A more variable initial proportion was needed to get the same effect with non-isogenic strains. The suspended solids that remain in the must after cold-settling decreased killer toxin effect. The addition of bentonite to the must avoided protracted fermentation and the suppression of sensitive strains; however, the addition of yeast dietary nutrients with yeast cell walls did not, although it decreased fermentation lag.

Effects of new Torulaspora delbrueckii killer yeasts on the must fermentation kinetics and aroma compounds of white table wine

“…But this time was reduced again in cold-settled non-filtered must, where EX1180-11C4 disappeared after just 1 day ( Figure 1D ). A plausible explanation for this behavior is the presence of grape particles through the fermentation, which might adsorb and inactivate the toxin produced by T. delbrueckii , as it was previously shown for toxins produced by S. cerevisiae ( Pérez et al, 2001 ). The S. cerevisiae EX85 strain also dominated the must fermentation when initially combined with 90% of the non-killer T. delbrueckii EX1180-2K - , although this latter strain remained at above 40% for 7 days in filtered must fermentation.…”

“…In particular therefore, the results showing that the T. delbrueckii Kbarr-1 strain dominated the low-turbidity (<100 NTU) sterile must fermentation when co-inoculated in a 90% initial proportion with 10% of S. cerevisiae wine strains are reliable. This initial proportion was much greater than that required for the S. cerevisiae killer K2 strain to dominate must fermentation ( Pérez et al, 2001 ), probably because of the faster growth and fermentation rates of S. cerevisiae relative to T. delbrueckii ( Mauricio et al, 1998 ). Increased must turbidity to values that are frequent in industrial wineries (100–250 NTU) had no relevant inhibitory effect on this T. delbrueckii Kbarr-1 domination, and, in particular, much less than the inhibitory effect that had been found previously using S. cerevisiae killer-K2 strains ( Pérez et al, 2001 ).…”

“…The availability of good-fermenting killer T. delbrueckii strains, able to kill the omnipresent wild Saccharomyces yeasts or to control the excessive growth of inoculated S. cerevisiae strains, could be an interesting tool with which to attain the desired domination of each inoculated yeast during must fermentation, and thus result in improved quality of the wine. The isolation of T. delbrueckii killer strains has been described previously ( Sangorrin et al, 2007 ), but they have not been used and analyzed in depth for winemaking as it has been S. cerevisiae K2 strains ( Pérez et al, 2001 ). The effect of S. cerevisiae killer strains on the growth of sensitive strains during must fermentation was seen to depend on the initial proportion of killer yeasts, the susceptibility of sensitive strains, and the treatment of the must.…”

“…An initial proportion of 2–6% killer yeasts was enough to suppress isogenic sensitive strains in sterile filtered must, although a greater initial proportion of killer yeasts may be needed to get the same effect against non-isogenic strains. The suspended solids that remain in the must after cold-settling were seen to reduce the killer toxin effect due to inactivation by absorption onto the grape particles ( Pérez et al, 2001 ).…”

Dynamic modelling of the killing mechanism of action by virus-infected yeasts

“…These infected cells are often detected in wine fermentation processes whereby killer yeasts contaminate starter cultures, killing the microbiological fermenting agents. Ratios as low as one killer yeast for every hundred sensitive yeasts was reported to eliminate the starter culture population within 24 h [4][5][6]. Stuck fermentations, which are characterized by high concentrations of acetaldehyde and lactic acid, are often a consequence and are typical of a very distasteful wine product [7].…”