A synergistic strategy coupling enzymatic isomerization with boronate affinity adsorption for efficient tagatose...

Tagatose, a functional ketose produced by galactose isomerization, faces production challenges due to reaction equilibrium limitations and the difficulty of separating similar sugars. This study developed an integrated strategy to overcome these hurdles by combining enzymatic catalysis with selective adsorption. Mesophilic and thermophilic _l-arabinose isomerases (_l-AIs), namely BtAI from Bacillus thermoglucosidasius and LfAI from Lactobacillus fermentum, were engineered to catalyze the conversion of galactose into tagatose. After systematic optimization, the BtAI-catalyzed galactose isomerization produced 15.05 g/L tagatose with a yield of 47.68 %, whereas the LfAI-catalyzed reaction produced 17.87 g/L tagatose with a yield of 53.05 %. In addition, dual-enzyme cascade systems combining β-galactosidase (β-Gal) with _l-AIs were constructed to explore their ability to valorize lactose for tagatose production. The BtAI-based dual-enzyme cascade system produced 23.93 g/L tagatose with a yield of 23.26 % from lactose, whereas the LfAI-based system resulted in 21.89 g/L tagatose with a yield of 19.72 %. To address purification and equilibrium constraints, a low-pK_a boronate affinity adsorbent (PBA@AR) with high tagatose selectivity was synthesized. Implementing a PBA@AR-mediated adsorption-assisted isomerization strategy drove the reaction equilibrium forward, increasing the final tagatose yield to 67.07 % while simultaneously achieving a product purity exceeding 95 %. This work provides an efficient approach for enhancing both the yield and purity in enzymatic ketose production.