Development of boronate affinity adsorbent bearing -B(OH)₂ and [sbnd]F groups with low pK_a value for enhanced production and purification of lactulose through adsorption-assisted bio-isomerization of lactose

In this study, a boronate affinity material (FA-5) with a low pK_a value was prepared to facilitate lactulose production. At physiological pH, 58.23 % of the B atoms in FA-5 existed in an sp³ hybridization state, and FA-5 demonstrated excellent adsorption capacity (94.78 mg/g) and selectivity (91.82 %) for lactulose from a 1:1 lactulose-lactose solution. Additionally, FA-5 demonstrated an exceptional capability for separating lactulose. The purity of lactulose increased by up to 6.82-fold in lactulose-lactose solutions with varying concentration ratios. A cascade system was formed by an immobilized enzyme-packed column with an FA-5-packed column to enhance lactulose production and purification. By adopting the adsorption-assisted isomerization strategy, the lactulose yield was improved from 52.50 % to 71.14 % with lactulose purity reaching 83.57 %. Moreover, the cascade system demonstrated excellent catalytic stability (86.28 %) and adsorption stability (93.68 %) over six consecutive cycles. The results highlight the potential of the cascade system for enzymatic production of lactulose.