Fructosylation of phenolic compounds by levansucrase from Gluconacetobacter diazotrophicus.

Fructosylation can significantly improve the solubility, stability and bioactivity of phenolic compounds, increasing their health benefits. Levansucrase from Gluconacetobacter diazotrophicus (LsdA, EC 2.4.1.10) was found to transfer the fructosyl unit of sucrose to different classes of phenolic compounds. Among the various acceptors tested, the isoflavone puerarin and the phenol coniferyl alcohol were the most efficiently fructosylated compounds, with conversion rates of 93% and 25.1%, respectively. In both cases, mono-, di-, and trifructosides were synthesized at a ratio of 37:14:1 and 32:8:1, respectively. Structural characterization of the puerarin mono-fructoside revealed that the enzyme transferred the fructosyl moiety of sucrose to the O6-position of the glucosyl unit of puerarin. The water solubility of fructosyl-β-(2→6)-puerarin was increased 23-fold, up to 16.2 g L-1, while its antioxidant capacity was only decreased 1.25-fold compared with that of puerarin.