Potentialities of yeasts in production of single-cell proteins (SCP).
Different local active yeasts were isolated from air, soils, and muddy sludges. Potentialities and capabilities of 67 yeasts isolates for formation of SCP (single-cell protein) were evaluated by their cultivation on the fermentation medium, containing diesel oil as sole carbon source to select the most efficient yeast isolates. Identification of the most active organisms revealed that Candida tropicalis and Yarrowia lipolytica were the most efficient yeasts, having potentialities for SCP production. Biochemical changes which occurred during the fermentative production of SCP by Candida tropicalis revealed that during the fermentation process a deep in pH towards the acid side was recorded, and this might be due to the formation of certain organic acids with the beginning of fermentation. Yields of yeast cell biomass increased with the increase of fermentation period, reaching its optimum at 168 h, above which a decline in SCP was observed. High diesel oil concentrations in the fermentation medium harmed yeast growth and consequently a decrease in cell biomass was observed, while low diesel oil concentrations, especially in the range of 40--60 ml/litre, gave high titres of SCP. Addition of diesel oil at different intervals of the fermentation process-promoted yield of SCP.