THE OPTIMIZATION OF A CO-CULTURE OF TWO DISTINCT YEASTS INTERACTING WITH EACH OTHER TO PRODUCE ETHANOL FROM MOLASSES AT HIGH TEMPERATURES

Jéssica Medina Gallardo (UNESP-IQ); Cecilia Laluce (UNESP-IQ)

Keeping temperatures at 30°C to 34°C in large-scale industrial bioreactors (a capacity of thousands of liters) in tropical climates has been a challenging task. Wild yeasts (Pichia, Candida species, Hanseniaspora, Issatchenkia and Metschnikowia) were detected by other authors in the following environments: a) spontaneous wine fermentation; b) indigenous fermented foods; c) traditional sourdough fermentation producing flavor compounds, d) natural fermentations of beverages in Africa and Asia, e) in Cacao seed fermentation in order to remove the bitter taste and to provide optimum flavor and aroma to the chocolate using strains of I. orientalis, f)  in sugar-cane molasses which were found to have strains capable of growing very well at 39°C and pH 2.0.  I. orientalis has also been detected in a variety of fermentation processes: during the tumultuous or late fermentation of natural wine cooperating with Saccharomyces in order to convert all the remaining sugar into ethanol. In addition, I. orientalis is more resistant to lactic acid and acetic acid than strains of S. cerevisiae. To obtain the data reported in the present work, growth of yeasts on solid medium (YPD, minimal medium) and liquid medium (sugar-cane molasses, synthetic medium in agitated batch cultures) were carried out. In fact, the data described in this work were from co-cultures which were started using mixtures of Saccharomyces cerevisiae and I. orientalis as inoculum. The isolates of I. orientalis of our culture collection showed great diversity concerning tolerance to temperature. The fermentation of molasses by one of the isolates selected for the present study was dependent on the presence of a strain of Saccharomyces cerevisiae. Within a fermentation time of 12 - 20h, it was possible to produce up to 7-8% ethanol (v/v) fermenting 10% molasses (ART) at 42°C without significant losses in viability. At concentrations of ethanol produced above 8% significant drops in viability were observed at 42°C during fermentation.