EFFECT OF NON-Saccharomyces YEAST FLOCCULATION ON Saccharomyces FERMENTATION PERFORMANCE

OSCAR ANTONIO SOSA; MARIA CRISTINA MANCA DE NADRA; MARTA ELENA FARÍAS

ESPAÑA

Congreso; INTERNATIONAL CONFERENCE ON ENVIRONMENTAL, INDUSTRIAL AND APPLIED MICROBIOLOGY (BioMicroWorld-2005).; 2005

Yeast flocculation is a cell-cell aggregation phenomenon of great interest in brewing and several other fermentation industries. Several explanations have been proposed for the flocculation of pure cultures of yeasts, in this case the phenomenon is called self-flocculation or auto-flocculation. According to lectin like theory, flocculation occurs as a consequence of the interaction between the specific flocculation proteins (lectins) present only in the flocculent cells and the carbohydrate residues (receptors) of the walls of neighboring cells; in this process, Ca2+ seems to induce the correct conformation of the lectins [1]. In the early stages of wine fermentation, a predominant growth of non-Saccharomyces yeasts with a poor fermentation power is observed. Hanseniaspora (Kloeckera) and Candida are the most frequent yeast as in spontaneous as in inoculated fermentation. It was determined that Kloeckera apiculata mc1 isolated from wine posses intense cell-cell interactions in MYPG medium and the mechanism of the flocculation is mediated by protein-carbohydrate interaction, stabilized by Ca2+[2]. This characteristic may be useful in modern biotechnology as it is an easy and cheap way of separating the cell biomass from the media at the end of fermentations. Despite the commercial importance, little is known about the effect of non-Saccharomyces yeasts flocculation on the other microorganisms involved in wine elaboration. Taking into account that Saccharomyces cerevisiae is the main yeast in the wine alcoholic fermentation, in this work we carried out in mixed culture the study of the effect of flocculent Kloeckera apiculata mc1 on fermentative capacity of a non-flocculent Saccharomyces cerevisiae strain. Considering the predominance of the non-flocculent yeast in the natural habitat, mixed culture were performed by mixing in a ratio 1: 2 Kloeckera apiculata and Saccharomyces cerevisiae, respectively. Pure cultures were used as controls. When the microorganisms were co-cultured an inhibition of Kloeckera apiculata flocculation was observed. The free apiculate cells remaining in suspension correspond to 95% of total Kloeckera apiculata cells. This value in pure culture corresponds to 65%. On the other hand, Saccharomyces cerevisiae shows in mixed culture a 21% increment of the cells that sediment. In pure culture this value corresponds to 5 %. This behaviour could be consequence of a higher entrapped of Saccharomyces into the floc formed by the apiculate yeast or could be result of a cell-cell interaction between both yeasts. Ethanol concentration diminish from 5,7 in pure culture of elliptic yeast to 4,9 g.l-1.day- 1 in mixed culture. These results may be considered during spontaneous wine fermentation. The flocculation capacity of Kloeckera apiculata mc1 modify the number of nonflocculent Saccharomyces strains cells in the media, interfering with its fermentative power and so altering the ethanol concentration in the final product.