Stabilized glycerol dehydrogenase for the conversion of glycerol to dihydroxyacetone

The biodiesel industry generates glycerol as a main by-product, and the conversion of glycerol to value-added products is an important issue. Glycerol dehydrogenase (GDH) can catalyze the conversion of glycerol to dihydroxyacetone (DHA), which is used as a tanning agent in cosmetics and is much more expensive than glycerol. In this study, GDH was adsorbed into magnetically-separable mesoporous silica with 38. nm mesocellular pores connected via 18. nm window mesopores (adsorbed GDH, called ADS), and further crosslinked via a simple glutaraldehyde treatment to prepare nanoscale enzyme reactors of GDH (NERs of GDH, called NER). When the stabilities of free and immobilized GDH were monitored in an aqueous buffer under shaking (200. rpm), the residual activities of the free GDH and ADS could no longer be detected after 8. days and 22. days, respectively, while the NER maintained 64% of its initial activity even after 24-day incubation. The time-dependent conversion of glycerol to DHA was measured for both ADS and NER not only by analyzing the generation of NADH spectrophotometrically (340. nm) but also via the HPLC analysis measuring the increase of the DHA peak. Magnetically-separable NER maintained 39% of its initial activity after seven cycles of repeated use, while the residual activity of ADS dropped to 13% of its initial activity after only two recycled uses.