Effect of crude glycerol, 2,3-butanediol, and acetoin initial concentrations on Enterobacter aerogenes ATCC 13048 growth in batch runs

The 2,3-butanediol (BD) and acetoin production from several carbon sources and microorganisms has been extensively studied, mainly due to the possibility of replacing petroleum derivatives by the diol. Crude glycerol is highlighted among the substrates that can be used to produce 2,3-BD. However, this carbon source contains impurities that can affect microbial metabolism. Furthermore, there are scarce studies about the inhibitory effect of fermentation products, such as 2,3-BD and acetoin, on the process. The aim of this study was to evaluate the effect of crude glycerol, 2,3-BD and acetoin initial concentrations on Enterobacter aerogenes growth and metabolism. For this purpose, batch runs were performed using crude glycerol concentrations varying from 20 to 80 g.L-1. To evaluate the inhibitory effect of 2,3-BD plus acetoin, batch runs were performed using product addition from 0 to 40 g.L-1. During batch runs performed using increasing crude glycerol concentrations, the values of maximum specific growth rates were decreasing, evidencing the metabolism inhibition possibly due to the osmotic pressure and substrate composition. In all batch runs, acetic and lactic acids, and ethanol were identified as co-products. In the case of fermentation products, the 2,3-BD plus acetoin initial concentration of 20 g.L-1 was found inhibitory to E. aerogenes growth by a reduction of 45% in maximum specific growth rate. The data also proved the major influence of 2,3-BD rather than acetoin on the overall rate of fermentation, since acetoin concentrations of up to 3.5 g.L-1 did not influence the E. aerogenes growth. Furthermore, the strain ability to adapt to the 2,3-BD and acetoin initial concentrations was demonstrated, opening possibilities for new processes strategies.