Exploitation of spoilage dates as biomass for the production of bioethanol and polyhydroxyalkanoates

The exploitation of agri-food wastes is of great importance for environmental and economic reasons. Date wastes are attractive biomasses that could be used as a carbon source for the growth of microorganisms to obtain added-value products. In this work, spoilage date syrup, containing 102.01 and 101.00 g/L of glucose and fructose, respectively, was assessed as a feedstock for the production of bioethanol and polyhydroxyalkanoates (PHAs) by Saccharomyces cerevisiae MEL2 and Cupriavidus necator DSM 545, respectively. The waste date syrup was first evaluated as a carbon source for microbial growth and resulted to sustain the growth of both strains. 47.95 g/L of ethanol, corresponding to the 93.52% of the theoretical yield, were obtained from the fermentation of date syrup by S. cerevisiae MEL2, here adopted as a proficient bioethanol yeast strain. Furthermore, C. necator DSM 545, a well-known PHAs-producer, was able to accumulate up to 79.20 % (w/w on dry mass) of PHAs. This study demonstrates that bioethanol and PHAs can be obtained from date wastes, contributing to developing cost-effective exploitation of these residues with economic and environmental advantages.