Die Bildung von Killertoxin und die Beeinflussung der Gärung durch Apiculatus-Hefen

Abstract

Formation of killer toxin by apiculate yeasts and interfernnce with fermentation Several strains of the frequently occurring apiculate yeast ( Hanseniaspora uvarum ) form a killer toxin (a protein) which inhibits a sensitive wine yea st ( Saccharomyces cereirisiae ). This toxin was partially concentrated by lyophilization and precipitation with e thanol. The toxin activity was determined with the agar diffusion method. The optimum of activity was observed at pH 4, but the killer toxin is also active at pH 3.5, the pH of grape must. The presence of apiculate killer yeasts s lowed the fermentation of a sensitive wine yeast ( S. cerevisiae 381). In mixed cultures of the killer strain H. uvarum 470 with S. cerevisiae the maximum inhibition of the latter was at 20 °C and at pH 3.5. Within 2 d about 95 % of the sensitive yeast cells were killed. Several days later the wine yeast resumed fermentation. The killer toxin delayed the normal fermentation by 10- 20 d. Depending on the ratio of cell numbers between the sensitive wine yeast and the apiculate killer yeast, the fermentation was suppressed for up to 15 d. When the cell number of wine yeasts was less than 0.01 % of the killer yeast cells ( H. uvarum 470) all sensitive cells were killed. Even at an inoculum of 106 cells/ml of S. cereirisiae a delay in the normal fermentation was observed when the sensitive yeast was added 2 d after the apiculate killer strain. By adding bentonite at a concentration of 0.01 % the interference of killer toxin with fermentation was prevented. The delay of normal fermentation which was caused by killer strains of H. uvarwn was not only observed in laboratory media but a lso in experiments with grape must.