2.7 Organic acids analysis
Organic acids in the supernatant after fermentation with ΔldhA -6 mutant were analyzed using an HPLC system equipped with a refractive index (RI) detector (Waters 2414, USA) and a ROA column (7.8 × 300 mm, Phenomenex, Torrance, CA) for the organic acids and an RPM column (4.6 × 300 mm, Phenomenex, Torrance, CA) for the fermentable sugars. The temperatures of the detector and column were maintained at 40 and 65 °C, respectively. The mobile phase was passed through the column at a flow rate of 0.6 mL per min with 5 mM sulfuric acid.