As for derivatization, 10 µL of filtered hydrolysated samples or standard were transferred into a 1.5 mL glass vial and 70 µL of borate buffer solution was added and mix well. Then, 20 µL of AccQ Flour reagent (3 mg mL−1 in acetonitrile) was added to the mixture and thoroughly mix through vortex for several seconds. Ten microliter of samples and standards were injected into the HPLC (Waters 2475, Waters Co., Milford, MA, USA) and the flow rate was set at 1 mL min−1. Analysis of the amino acids was performed with AccQ Tag (3.9×150 mm) column.