Cheongguk-jang is a Korean traditional food produced by natural fermentation of boiled soybean. In cheongguk-jang, bacilli are dominant bacteria and produce highly viscous poly-c-glutamic acid (c-PGA), which improves human health functions. The purpose of this experiment was to find maximum production condition for the c-PGA content during fermentation of cheongguk-jang with Bacillus subtilis 168. The most viscous cheonggukjang was produced when soybean was cooked at 121°C for 60 min in the presence of 50%(w/w) added water, followed by fermentation at 40°C for 2 days. Additional conditions for maximum production of c-PGA were the addition of 0.1%(w/w) FeCl 3 Á6H 2 O, 3.0%(w/w) lactose and 3.0%(w/ w) yeast extract as nutrients of inorganic salts, carbon source and nitrogen source, respectively. The three conditions did not show cumulative effect on the c-PGA production and the addition of iron salt induced the most c-PGA (0.97 ± 0.05%(w/w)), which corresponded to 2.7 times of the content in control cheongguk-jang.
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