Fig. 4

Time course of acetoin and succinic acid co-production by fed-batch fermentation using strain EC∆budC∆ldhA under the optimized conditions. a Glucose, acetoin, succinic acid, b by-product. The experiments were conducted in 50 mL of fermentation medium containing 60 g L⁻¹ glucose in a 250 mL flask. NaHCO₃ (2.5, 1, 1, 5, 5, 5 and 2 g L⁻¹) was added at 0, 6, 12, 24, 36, 48, and 60 h of fermentation, respectively. Glucose (60, 25, 35, 35, and 35 g L⁻¹) was added at 0, 12, 24, 36, and 48 h of fermentation, respectively. Samples were withdrawn every 12 h for detection of cell density and concentration of substrates and products