Limited oxygen conditions as an approach to scale-up and improve D and L-lactic acid production in mineral media and avocado seed hydrolysates with metabolically engineered Escherichia coli.

The effectiveness of micro-aeration on lactate (LA) production by metabolically engineered Escherichia coli was evaluated in 1 L bioreactors containing mineral media and glucose (70 g/L). Volumetric oxygen transfer coefficients (ka) between 12.6 and 28.7 h increased the specific growth rate (µ) and volumetric productivity (Q) by 300 and 400%, respectively, without a significant decrease in lactate yield (Y), when compared with non-aerated fermentations. A ka of 12.6 h was successfully used as a criterion to scale-up the production of L and D-lactate from 1 to 11 and 130 L. Approximately constant Q and Y values were obtained throughout the fermentation scale-up process. Furthermore, a D-lactogenic fermentation was carried out in 1 L bioreactors using avocado seed hydrolysate as a culture medium under the same ka value, displaying high Q and Y.