Distribution of poly--glutamate (-PGA) producers in Korean fermented foods, Cheongkukjang, Doenjang, and Kochujang

Poly-y-glutamate (${\gamma}$-PGA) has great potential as a biodegradable polymer in a broad range of industrial fields such as food, cosmetics, medicine and water treatment. In order to isolate ${\gamma}$-PGA producers that are suitable for specific industrial applications, 653 Bacillus-like strains were isolated from 439 varieties of three Korean fermented foods, Cheongkukjang, Doenjang, and Kochujang, which were collected from different regions across Korea. A very high level of ${\gamma}$-PGA production was demonstrated in 4.7%, 1.8%, and 3.0% of the Bacillus-like strains isolated from Cheongkukjang, Doenjang, and Kochujang samples, respectively, which produced a viscous substance to such extent that it overflowed to the lid of the plate on the glutamate-dependent ${\gamma}$-PGA production plates. On glutamate-independent ${\gamma}$-PGA production plates, 5.1%, 5.9%, and 6.1% of Bacillus-like strains isolated from Cheongkukjang, Doenjang, and Kochujang samples, respectively, showed high production. The maximum ${\gamma}$-PGA production yields were 32.5 g/L and 5 g/L, depending on the purification methods in the glutamate-dependent media, with the higher yield resulting from a simple precipitation of ${\gamma}$-PGA by either methanol or ethanol and dialysis. The viscous substance produced by each strain showed different morphological characteristics, suggesting that isolated ${\gamma}$-PGA producers could produce various types of ${\gamma}$-PGA.