Issue 21, 2019

A green-by-design bioprocess for l-carnosine production integrating enzymatic synthesis with membrane separation

Abstract

L-Carnosine (L-Car, β-alanyl-L-histidine) is a bioactive dipeptide with important physiological functions. Direct coupling of unprotected β-Ala (β-alanine) with L-His (L-histidine) mediated by an enzyme is a promising method for L-Car synthesis. In this study, a new recombinant dipeptidase (SmPepD) from Serratia marcescens with a high synthetic activity toward L-Car was identified by a genome mining approach and successfully expressed in Escherichia coli. Divalent metal ions strongly promoted the synthetic activity of SmPepD, with up to 21.7-fold increase of activity in the presence of 0.1 mM MnCl2. Higher temperature, lower pH and increasing substrate loadings facilitated the L-Car synthesis. Pilot biocatalytic syntheses of L-Car were performed comparatively in batch and continuous modes. In the continuous process, an ultra-filtration membrane reactor with a working volume of 5 L was employed for catalyst retention. The dipeptidase, SmPepD, showed excellent operational stability without a significant decrease in space–time yield after 4 days. The specific yield of L-Car achieved was 105 gCar gcatalyst−1 by the continuous process and 30.1 gCar gcatalyst−1 by the batch process. A nanofiltration membrane was used to isolate the desired product L-Car from the reaction mixture by selectively removing the excess substrates, β-Ala and L-His. As a result, the final L-Car content was effectively enriched from 2.3% to above 95%, which gave L-Car in 99% purity after ethanol precipitation with a total yield of 60.2%. The recovered substrate mixture of β-Ala and L-His can be easily reused, which will enable the economically attractive and environmentally benign production of the dipeptide L-Car.

Graphical abstract: A green-by-design bioprocess for l-carnosine production integrating enzymatic synthesis with membrane separation

Supplementary files

Article information

Article type
Paper
Submitted
13 avg 2019
Accepted
23 sep 2019
First published
27 sep 2019

Catal. Sci. Technol., 2019,9, 5971-5978

A green-by-design bioprocess for L-carnosine production integrating enzymatic synthesis with membrane separation

D. Yin, J. Pan, J. Zhu, Y. Liu and J. Xu, Catal. Sci. Technol., 2019, 9, 5971 DOI: 10.1039/C9CY01622H

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