Recycling preparation of high-purity tagatose from galactose using one-pot boronate affinity adsorbent-based adsorption-Assisted isomerization and simultaneous purification

Abstract

D-tagatose, one of the most valuable low-calorie rare sugars, is in huge market demand in the current food and medicine industries due to its excellent physiological functions. The production and recovery of high-purity tagatose from galactose isomerization presents two major challenges due to the exist thermodynamically limitation and their high structural similarity. Interestingly, the prepared macroporous polymeric boronate-affinity adsorbent (PBA-adsorbent) exhibited superior binding affinity towards tagatose than galactose. In a 1:1 galactose-to-tagatose binary solution, the PBA-adsorbent presented a much higher adsorption capacity towards tagatose (QTag = 53.94 mg/g) than galactose (QGal = 7.06 mg/g) and therefore enabled an excellent purification efficiency. Herein, a novel strategy for combining the PBA-adsorbent-based adsorption-assisted galactose-to-tagatose isomerization and simultaneous purification of tagatose, where the isomerization of galactose and the recovery of tagatose occur concurrently in the same PBA-adsorbent loaded column system, is presented. Through in situ selective capture of the newly formed tagatose, while leaving behind the galactose, the applied strategy enables an improved galactose-to-tagatose isomerization equilibrium with the yield of tagatose reaching up to 52.92%. Simultaneously, the adsorbed tagatose can be recovered efficiently via a two-stage sequential desorption process, which improves the tagatose purity to ∼ 85% with a promising recovery ratio of 87.42%. Remarkably, both the prepared PBA-adsorbent and the applied strategy exhibited excellent operational stability. Through pH-controlled desorption, the loaded PBA-adsorbent and the column system can be easily regenerated, well proving their good durability and recyclability in sustainable industrial applications. Furthermore, a possible mechanism involving the effect of boron-to-sugar ratio, the variation of boron intrinsic chemical states, and pH-responsive selective adsorption and sequential desorption was proposed to help understand how the applied PBA-adsorbent based strategy facilitates the highly efficient galactose-to-tagatose isomerization.