Nitrogen availability of grape juice limits killer yeast growth and fermentation activity during mixed-culture fermentation with sensitive commercial yeast strains

Abstract

The competition between selected or commercial killer strains of type K2 and sensitive commercial strains of Saccharomyces cerevisiae was studied under various conditions in sterile grape juice fermentations. The focus of this study was the effect of yeast inoculation levels and the role of assimilable nitrogen nutrition on killer activity. A study of the consumption of free amino nitrogen (FAN) by pure and mixed cultures of killer and sensitive cells showed no differences between the profiles of nitrogen assimilation in all cases, and FAN was practically depleted in the first 2 days of fermentation. The effect of the addition of assimilable nitrogen and the size of inoculum was examined in mixed killer and sensitive strain competitions. Stuck and sluggish wine fermentations were observed to depend on nitrogen availability when the ratio of killer to sensitive cells was low (1:10 to 1:100). A relationship between the initial assimilable nitrogen content of must and the proportion of killer cells during fermentation was shown. An indirect relationship was found between inoculum size and the percentage of killer cells: a smaller inoculum resulted in a higher proportion of killer cells in grape juice fermentations. In all cases, wines obtained with pure-culture fermentations were preferred to mixed-culture fermentations by sensory analysis. The reasons why killer cells do not finish fermentation under competitive conditions with sensitive cells are discussed.

Non‐Saccharomyces and Saccharomyces strains co‐fermentation increases acetaldehyde accumulation: effect on anthocyanin‐derived pigments in Tannat red wines

“…Fermentation activity was measured by CO 2 weight loss, expressed in g/100 ml. Purity control of the different assays was determined at the end of the fermentations, using WL nutrient medium for colony growth differentiation (Medina et al ., ; Pallmann et al ., .…”

Production of  fermentation aroma compounds bySaccharomyces cerevisiaewine yeasts: effects of yeast assimilable nitrogen on two model strains

“…Saccharomyces cerevisiae strains utilized were: Montrachet UCD 522 (University of California, Davis), referred to as M522 in this work, and KU1 [Uruguayan selected strain, (Carrau et al, 1993;Medina et al, 1997)]. Both strains are used in the commercial production of wine.…”

“…This experimental approach has, however, not proved to be suitable because S. cerevisiae yeast strains that show similar profiles of assimilable nitrogen consumption can nevertheless produce very different profiles of fermentation rate and aromatic compounds under industrial conditions of lower initial nitrogen levels (Jiranek et al, 1991;Carrau, 2003;Taillandier et al, 2007). There are few reports of investigations into the sensory characteristics of wines made with different strains under low nitrogen fermentation conditions (Carrau et al, 1993;Medina et al, 1997;Carrau, 2003). Only recently, have the first chemometric studies provided data on the significance of yeast aroma compounds to perceived flavor in wine (Smyth et al, 2005).…”

Monitoring of killer yeast populations in mixed cultures: influence of incubation temperature of microvinifications samples

“…Toxins produced by killer yeasts exclude other species from their habitats, and killer yeasts have several applications in the food and fermentation industries. It is important to determine the degree of real killer yeast dominance under different fermentation conditions because it has been found that stuck and sluggish wine fermentations depend on the ratio of killer/sensitive cells (Shimizu 1993;Magliani et al 1997;Medina et al 1997;Musmanno et al 1999).…”