Optimization of medium constituents and fermentation conditions for the production of L-Glutamic acid by the coimmobilized whole cells of Micrococcus glutamicus and Pseudomonas reptilivora

Abstract

Statistical experimental design was used to optimize medium constituents and the conditions of fermentation, viz., temperature, pH and the time of fermentation. Higher yields of L-glutamic acid (37.1 kg/m 3 ) was obtained after optimizing medium components and the conditions of fermentation. The optimal levels of medium components were: 61.5575 kg/m 3 glucose, 7.3272 kg/m 3 urea and 1.783 lg/dm 3 biotin. The optimum productivity was achieved using optimized medium at the fermentation temperature of 33.7°C, initial pH 7.74, and at the time of fermentation of 58.4 h. IntroductionL-glutamic acid has widespread use throughout the world, this amino acid is of special interest because of its¯avour, sweet taste, and acidic character. L-glutamic acid is used as a seasoning agent and as a starting material for the synthesis of various kinds of speciality chemicals [1]. The annual production of monosodium glutamate produced extensively by fermentation exceeds 370,000 tonnes [2]. The study of L-glutamic acid fermentation gained importance because of its wide spread applications in the food and pharmaceutical industry. L-glutamic acid was produced in the earlier days by the acid hydrolysis of wheat glutten or soyabean protein. Over a period of years, L-glutamic acid producing microorganisms were isolated and subsequent research resulted in fermentative process for the production of L-glutamic acid [3]. At present almost all the L-glutamic acid available commercially is being produced by fermentation process [4±5].The present study involves the optimization of medium constituents for the production of L-glutamic acid by coimmobilized whole cells of Pseudomonas reptilivora and Micrococcus glutamicus, followed by the optimization of physical operational variables like initial pH, temperature and time of fermentation. Conventional practice of single factor optimization by keeping other involving factors at unspeci®ed constant level does not depict the combined effect of all the factors involved. Also this method requires to carry out a number of experiments to determine the optimum levels, which are untrue. These drawbacks of single factor optimization process can be eliminated by optimizing all the affecting parameters collectively by statistical experimental design. Experimental design using response surface methodology (RSM) [6±8] was used in the present investigation to optimize the medium constituents and the conditions of fermentation of L-glutamic acid production by coimmobilized whole cells of Psedomonas reptilivora and Micrococcus glutamicus. Materials and methods OrganismsPseudomonas reptilivora NCIM 2598 and Micrococcus glutamicus NCIM 2168, obtained from National Chemical Laboratory, Pune, India, were used through out this study. Growth medium and growth conditionsThe cultures were maintained on agar slants having composition (kg/m 3 ): glucose ± 10, beef extract ± 10, peptone ± 10, NaCl ± 5 and agar agar ± 20. The pH of the medium was adjusted to 7.0 and incubated at 37°C for 36 h. For the seed culture development, ...

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