LGlutaminase

L-glutaminase (L-glutamine amidohydrolase - E.C. 3.5.1.2) is an important enzyme deam-idating L-glutamine, which plays a major role in the cellular nitrogen metabolism of both prokaryotes and eukaryotes. L-glutaminase is useful in the food industry as it increases the glutamic acid content of the fermented food, thereby imparting a unique flavor. Because the sources for L-glutaminases are limited, the search for potential microbial strains that produce the enzyme in high titres with novel properties for their industrial production is being pursued extensively around the world (31).

L-glutaminase can be produced by many bacterial strains, such as Escherichia coli, Pseudomonas sp., Acinetobacter sp., Bacillus sp., Proteus morganni, P. vulgaris, Xanthomonas juglandis, Erwinia carotovora, E. aroideae, Serratia marcescens, Enterobacter cloacae, and Klebsiella aerogenes. It can also be produced by Aerobacter aerogenes, fungi such as Aspergillus sojae and A. oryzae, and yeast cultures such as Hansenula, Cryptococcus, Rhodotorula, Candida scottii, Cryptococcus albidus,

C. laurentii, Candida utilis, and Torulopsis candida (31).

One of the major advantages of SSF system for L-glutaminase production lies in cultivation of salt tolerant microbial cultures, which may have better application in food processes involving high salt concentration, such as soy sauce production which requires as high as 20-25% salt concentration. From this point of view, marine microorganisms have been explored and exploited. There seems to be enormous scope for the investigation of deriving new products of economic importance from potential marine microorganisms. Considering the fact that the marine environment, particularly sea water, is saline in nature and chemically closer to human blood plasma, it could be anticipated that this could provide microbial products; in particular, enzymes, that could be safer, having less toxicity and fewer side effects, when used for human application (31).

When SSF was carried out using saline tolerant yeast Zygosaccharomyces rouxii with agro-industrial substrates such as coconut oil cake, groundnut oil cake, wheat bran, and sesamum oil cake, 2.2 and 2.17 U enzyme/gram dry substrate (gds) were produced from wheat bran and sesamum oil cake, respectively. Under optimized physico-chemical conditions, enzyme yields increased to 7.5 and 11.61 U/gds for these, respectively, which is 3.5-5 times higher than the initial (without optimization) production (34).

L-glutaminase has also been produced in SSF using inert substrates such as polystyrene (100). A marine organism, Vibrio costicola, was used for solid culturing (35,100). Another marine isolate, Beauveria species, has also been used for L-glutaminase production (101). However, it was necessary to supplement the fermentation medium with NaCl at high concentrations (~10%) or sea-water when using such cultures. In both cases, enzyme production was growth associated.

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