Amino acid determination
The amino acid composition of the samples was analyzed by using an A300 automatic amino acid analyzer (Membra Pure GmbH, Germany). Hydrochloric acid was employed to hydrolysis ginseng extract at 110 °C for 24 h. The hydrolyzed extract was filtered into a 25 mL volumetric flask. Then, 1 mL sample was absorbed and deacidified at 60 °C in a vacuum until a small amount of stain was left at the bottom. The tested buffer was added and mixed with the stain, and the resulting solution was filtered through a 0.45 μm filter for analysis.