Preparation of eutectic substrate mixtures for enzymatic conversion of ATC to L-cysteine at high concentration levels

High concentration eutectic substrate solutions for the enzymatic production of L-cysteine were prepared. Eutectic melting of binary mixtures consisting of D,L-2- amino-Δ²-thiazoline-4-carboxylic acid (ATC) as a substrate and malonic acid occurred at 39 °C with an ATC mole fraction of 0.5. Formation of eutectic mixtures was confirmed using SEM, SEM-EDS, and XPS surface analyses. Sorbitol, MnSO₄, and NaOH were used as supplements for the enzymatic reactions. Strategies for sequential addition of five compounds, including a binary ATC mixture and supplements, during preparation of eutectic substrate solutions were established. Eutectic substrate solutions were stable for 24 h. After 6 h of enzymatic reactions, a 550 mM L-cysteine yield was obtained from a 670 mM eutectic ATC solution.