Automated amino acid analyzer

Ginseng samples were hydrolyzed in HCl (hydochlric acid) (6 M), and the pH was adjusted to 2.2 for all amino acids except tryptophan. Tryptophan samples were hydrolyzed in sodium hydroxide solution, and the pH was adjusted to 5.2. Individual amino acids were determined by comparison using an automated amino acid analyzer (Hitachi, Tokyo, Japan). γ-Aminobutyrate (GABA) was extracted as previously described by Baum et al [15] (link) with modifications. The ground samples (200 mg) were thawed in 800 μL of a mixture of methanol: chloroform: water 12:5:3 (v/v/v). The mixture was vortexed and then centrifuged at 12,000g for 15 min. The supernatant was collected, and 200 μL chloroform and 400 μL water were added to the pellet. The resulting mixture was vortexed and centrifuged for 15 min at 12,000g. The supernatant was collected and combined with the first supernatant and recentrifuged to obtain the upper phase. The collected samples were dried in a freeze-dryer and dissolved in water. The resulting samples contained GABA and other amino acids. Each sample was passed through a 0.45 μL filter and analyzed using an automated amino acid analyzer after 6-aminoquioyl-N-hydroxysuccinimidyl carbonate derivation.