The aim of this work was to study the cellular viability of the yeast S. cerevisiae in mixed culture with L. fermentum, considering the growing conditions and bacterial metabolic products. The microorganisms were cultivated individually in sugar cane juice supplemented with yeast extract and peptone. Yeast viability was investigated in mixed culture with active bacterial culture and with inactivated bacterial culture (by heat sterilization or by addition of antimicrobial agents). Deflocculation tests were performed on yeast flocculated cultures using peptidohydrolases group enzymes (papain, bromelin and ficin). In mixed active culture, yeast viability reduction of 96% was noticed after 12 h. In assays using the inactivated bacterial culture, reductions were between 50 to 60% during the first 12h, and reaching 80-90% after 24h. The influence of bacterial metabolic products on yeast viability was observed. A deflocculation ability of papain, bromelin and ficin, not yet reported in the litterature, was also observed, confirming the protein involvement in the floc formation by L. fermentum.
viability; flocculation; Saccharomyces cerevisiae; Lactobacillus fermentum