The effect of steaming on the free amino acid contents and antioxidant activity of ginseng
This study was carried out to investigate the changes in the free amino acid contents and antioxidant activity of Panax ginseng induced by steaming at different temperature. For this purpose, white ginseng (WG) was steamed at 100°C (RG), and 120 °C (SG) using an autoclave.
HPLC analysis of amino acids  revealed that most free amino acids were decreased significantly by steam treatment, with the greatest reduction observed in SG. Total content of free amino acids, 17.9mg/g in WG was reduced to 12.2mg/g in RG and 2.79mg/g in SG. The content of arginine, which is known to be the most predominant free amino acid in ginseng, was 10.4mg/g in WG decreased to 1.38mg/g in SG. In particular, β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), a neurotoxin , was reduced by 92.9% in SG.
In contrast, the level of Maillard reaction product (MRP) increased with steaming process, which suggests that the reduction of free amino acids is attributed to the extent of the Maillard reaction. Based on MRP being useful antioxidant, the radical scavenging activity against free radical produced by 2,2'-azobis-(2-amidinopropane) dihydrochloride was evaluated. Radical scavenging activities for WG, RG, and SG at 60min were 35, 62 and 78% respectively. Water-soluble fraction of SG showed the most potent antioxidant activity. We believe that high quality of ginseng can be obtained by steaming ginseng at higher temperature, in that a neurotoxin β-ODAP sharply decreases and the antioxidant activity remarkably increases .
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