2.5. Determination of Organic Acids

The organic acids in samples were analyzed by using Agilent 1260 Infinity II HPLC equipped with a DAD detector (Agilent Technologies Inc., Santa Clara, CA, USA). Separation and quantification of organic acids were performed at 210 nm with an Agilent Poroshell 120 EC-C18 column (4.6 × 150 mm, 4 μm). Two eluents, filtered through a 0.45 μm durapore membrane pore filter were used as mobile phases: eluent A: 0.5% (w/v) KH₂PO₄ (pH 2.3), eluent B: methanol, the elution condition was isostatic elution with A:B of 97:3 (v/v). Injection volume was 10 μL, flow rate was 0.7 mL/min, and column temperature was 35 °C.