vinegar samples (2 mL) were centrifuged (6000 g, 5 min) and filtered
(0.22 mm Millipore filter). The chromatographic apparatus consisted of
a Spectra-Physics P200 HPLC including a SP 8450UV-VIS detector for
measuring the absorbance at 254 nm. The column used was a 150¥4.6
mm, 5 mm C18 Spherisorb ODS resin from Tracer Analytical
(Barcelona, Spain). The column was thermostated at 25°C.