Abstract
A total of eight cultivable purified Egyptian yeast phenotypes were isolated from different sources, including fruits, juices and paste, and were compared to a baker's yeast factory reference strain. Genotypic characterization of the most promising new isolate (RO1) confirmed its identification as a Saccharomyces cerevisiae strain. In a shake-flask experiment, the Plackett-Burman multi-factorial design was applied to identify factors that considerably affect the RO1 growth rate. Together with the components of the factory molasses-based medium, six other culture factors, hypothesized to affect yeast biomass production, were examined as independent variables. The calculated main effect results and P-values suggested that by increasing the level of molasses, diammonium phosphate and inoculum size, compared to the factory settings, and by supplementing the medium with yeast extract, calcium pantothenate (vitamin B5) and trace elements, the RO1 biomass production was improved. Application of the predicted near-optimum fermentation conditions with scaling up the culture medium to 22 L in a 40 L airlift bioreactor resulted in 93 g L-1 biomass production, which represented approximately a 1.5-fold increase, when compared to the reference culture condition. Moreover, the dough raising test indicated that the newly isolated yeast strain RO1 caused a 1.75-fold increase in the fermentative power, when compared to the factory reference strain.