Samples analysis was carried out using a Dionex HPLC sys- tem with a photodiode array detector and Chromeleon software(Dionex), an Ultrabase C18 column (100 × 4.6 mm, 2.5 m) and a mobile phase of methanol: water pH 2.5 (adjusted with metaphosphoric acid, 15:85, v/v), 0.2 mL/min flux and injection volume 10 L. The temperature of the column was set at 35 ◦C.The method was calibrated with a curve of an ascorbic acid standard solution in 2% metaphosphoric acid,with concentrations between 1 and 100 g/mL.