Immobilization of Enterococcus faecalis cells with chitosan: A new process for the industrial production of l-citrulline

• A procedure for industrial immobilization of cells with chitosan in one step.
• Cells in fermentation broth immobilized without cell separation step.
• l-Citrulline production in tons scale with average conversion of 96.9%.

A new immobilization process using chitosan was developed for use in l-citrulline production. In this process, a cell suspension of Enterococcus faecalis and chitosan solution were mixed and cross-linked with glutaraldehyde. After treatment with a solution of saturated sodium bicarbonate, stirring, and washing, the immobilized cells were filtered. A fermentation broth of E. faecalis cells containing arginine deiminase was used for immobilization without the use of a cell-separation step and then compared with immobilized separated cells in a 1.0-L batch conversion. Cells immobilized with fermentation broth showed increased operational stability and were used in scale-up procedures. On an industrial scale, 210 kg of cells immobilized from 2000 L of fermentation broth was used for a 2000-L reaction. After five batches, 1000 kg of l-arginine was converted to 974.6 kg of l-citrulline, yielding 733.5 kg of the final product. The results demonstrate the feasibility of immobilization using chitosan on an industrial scale.

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