Determination of organic acids
Organic acids were determined by ionic chromatography with photodiode array detection (Waters 2998, Waters Corporation, Italy). Separation was achieved on a cation exchange column (Aminex 87-H column, 300 × 7.8 mm, 9 μm, Bio-Rad) using an isocratic elution with 10 mM H2SO4 as carrier, at a flow rate of 0.6 mL min-1. Detection was carried out at 210 nm. Standard carboxylates were prepared as individual stock solutions using Sigma (Italy) reagent grade compounds, and then combined to give diluted working standards to be used for retention time comparison and for quantification.