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Year: 2013  |  Volume: 12  |  Issue: 1  |  Page No.: 25 - 35

Production of a Novel Salt-tolerant L-glutaminase from Bacillus amyloliquefaciens Using Agro-industrial Residues and its Application in Chinese Soy Sauce Fermentation

Mao Ye, Xi Liu and Liyun Zhao    

Abstract: L-glutaminase could hydrolyze L-glutamine to L-glutamic acid which is an important ‘Umami’ substance. To obtain a salt-tolerant L-glutaminase for application in Chinese soy sauce fermentation, B. amyloliquefaciens Y-9 producing salt-tolerant L-glutaminase was isolated from mangrove sediment. The production of L-glutaminase in Solid State Fermentation (SSF) using agro-industrial residues was optimized using a central composite design of the Response Surface Methodology and the enzyme was purified which was used for further characterization including the optimum and stability of pH and temperature, effect of metal ions, substrate specificity and application to soy sauce fermentation. Under optimized conditions the experimental maximum yield of L-glutaminase reached 19.64±0.63 U gds-1 which is the highest yield obtained in SSF so far. The L-glutaminase was purified to homogeneity with final specific activity of 196.2 U mg-1 protein. The enzyme showed high activity (68% of the original activity) in the presence of 20% NaCl. The enzyme was most stable at pH 5.0 and was highly stable over an acidic pH range (3.0~7.0). These results indicate that this enzyme has a higher salt tolerance and an acidic stability. Furthermore, in Chinese soy sauce fermentation model reaction, the addition of glutaminase from B. amyloliquefaciens Y-9 was highly effective for the production of glutamic acid. This study indicates a possibility to establish economical large-scale production of L-glutaminase and this enzyme is suitable for application in soy sauce liquid fermentation with high-salt process.

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