키틴분해 박테리아 Bacillus idriensis (CGH18)의 항산화 활성

Abstract

Salt-fermented seafood sauce, called jeot-gal is one of the popular Korean traditional sauses and has been used to season other Korean food. It is made with various seafoods, such as shrimp, oyster, shellfish, fish, fish eggs, crab, and fish intestine. The seafood is salted and fermented for 2-3 months; then spices are added later to give its distinctive flavor. We considered that salt-fermented seafood' s high storability would be greatly contributed by antioxidizing capacity of microorganism that inhabits oxidation in salt fermented-seafood. This capacity to avert spoilage would also be due to the antioxidant produced by the microorganism. Crab, one of people' s favorite types of seafood, is one ingredient founf in salt-fermented seafood sauces. Its shell contains a polysaccharide called as chitin which is slow to decompose. Therefore, the problem is that consumption of crab generates crab shell as a waste, and this waste pollutes the environment.

Therefore, salt-fermented food sauce made with crab will be a good source of a microorganism that may decompose chitin and prevent oxidation of seafood.

The research team tried to isolate microorganisms to show antioxidizing and chitin-decomposing activities in colloidal chitin culture medium. As a result, a bacterium CGH18 was isolated from crab marinated in Soy Sauce and identified as Bacillus idriensis by 16S rDNA sequence homology search. B. idriensis exhibited optimal growth condition of pH, temperature, and culture time at 7.0, 25℃ and 48 h, respectively.

The culture broth was extracted repeatedly with EtOAc for 1 hour using sonication. Its crude extracts were partitioned between n-BuOH and H2O. The organic layer was further partitioned between CH2Cl2 and H2O. Antioxidant activities of crude extract and its solvent fractions were evaluated using five different activity tests, including the degree of occurrence of intracellular reactive oxygen species (ROS), peroxynitrite (ONOO−), and lipid peroxidation, as well as the extent of GSH level, and oxidative damage of genomic DNA. All fractions exhibited significant antioxidant activity in bioassay systems used. In particular, the CH2Cl2 fraction showed the strongest antioxidant activity among the solvent fractions. Further purification of the CH2Cl2 fraction by various chromatographic methods resulted in the isolation of two diketopiperazine (compounds 1-2). Their chemical structures were determined by extensive 2D NMR experiments such as 1H gDQCOSY, TOCSY, NOESY, gHMQC, and gHMBC, and by comparison with published spectral data.