Ethanol production by two selected osmotolerant yeast cultures

A collection of 235 yeast strains has been obtained from sources with high sugar content. Fruit juices, agave and cane syrups and molasses, as well as artisanal fermented foods and beverages were screened for that purpose.  The cultures were isolated and tested in a complex medium (MDS) using a high glucose concentration 40% (w/w). Two moderately osmotolerant yeast cultures (Prg and R2B4), were selected for their ability to actively ferment natural substrates, including sugarcane blackstrap molasses and honey. A medium composed of honey and molasses was used for liquid static fermentation at 30 ºC. In order to determine the catabolic products from the selected strains without any nutrient supplementation, samples from fermentation musts were taken at 60, 120 and 240 h. The samples were analyzed for sugar content, cell pellet dry weight and catabolite concentration (both by HPLC and by GC-MS). Both strains were good ethanol producers: Prg produced 74.95 mg/ml; and R2B4 38.07 mg/ml. The strains also produced high value added organic acids (lactic, succinic, itaconic, acetic and formic acid). Prg belongs to the genus Candida, whereas R2B4 to the genus Pichia. Potential applications for biofuels and chemicals are discussed.