Fed-batch strategies for the enhanced biotransformation of cis-epoxysuccinate to L-( +)-tartrate

L-( +)-Tartaric acid is a valuable organic acid with broad applications in the food, pharmaceutical, and chemical industries. Its eco-friendly synthesis typically relies on the enzymatic hydrolysis of cis-epoxysuccinate (CES) catalyzed by cis-epoxysuccinate hydrolases (CESHs), but conventional single-batch processes suffer from low space-time yields and poor continuity. To address these challenges, we devised two complementary fed-batch strategies to simplify the enzyme-product separation by exploiting differences in their solubilities. Strategy A employs carrier-free cross-linking immobilization of whole cells using 0.02% glutaraldehyde and 0.1% polyethylenimine. In this system, both the substrate sodium cis-epoxysuccinate (CESNa) and the product sodium L-( +)-tartrate remain soluble, while the enzyme is retained in the insoluble cell matrix. Under fed-batch operation, this configuration achieves a space-time yield of 150 g L^-1 h^-1. Strategy B uses cell-free extract of CESH to hydrolyze calcium cis-epoxysuccinate (CESCa) with inherently low solubility. Here, the enzyme is fully soluble but the L-( +)-tartrate formed precipitates as an insoluble calcium salt, allowing easy separation of the product from the reaction mixture. This approach overcomes potential substrate inhibition and minimizes sodium-ion discharge, delivering a space-time yield of 136 g L^-1 h^-1 and a specific productivity of 484 g_product/g_catalyst. Both the soluble-product/insoluble-enzyme system (A) and the insoluble-product/soluble-enzyme system (B) represent effective strategies to streamline downstream processing and markedly enhance productivity. Together, they offer a viable route to scalable and cost-effective industrial production of L-( +)-tartaric acid.