Evaluation of the non-conventional yeast strain Wickerhamomyces anomalus (Pichia anomala) X19 for enhanced bioethanol production using date palm sap as renewable feedstock

In the present study the non-conventional yeast Wickerhamomyces anomalus X19, was evaluated as biocatalyst for direct, low cost bioethanol production, using natural date palm sap (DPS) as substrate. Initial experiments were conducted with synthetic media in order to characterize the strain in terms of its nitrogen requirements, the effect of initial substrate concentration on the ethanol yields and the main kinetic constants during alcoholic fermentation. Subsequently, the effect of aerobic or anaerobic conditions was assessed with DPS as substrate, in batch mode and the possible improvement of ethanol yields was further investigated via fed batch experiments. It was shown that W. anomalus X19 was not inhibited by low pH (<3) and high initial sugar concentrations (up to 160 g/L), leading in all cases to ethanol yields that exceeded 80% of the theoretically estimated values. The highest ethanol concentration from DPS fermentation was achieved in fed batch experiments, reaching 73.11 g/L and the ethanol yield was 0.46 g/g sugars, which corresponded to more than 90% of the theoretical maximum.