Properties of a novel polydatin‐β‐ d ‐glucosidase from Aspergillus niger SK34 .002 and its application in enzymatic preparation of resveratrol

BACKGROUND: Resveratrol and its glucoside polydatin are the main stilbenes in Polygonum cuspidatum. Resveratrol has become the subject of intensive research over the past two decades owing to its outstanding pharmacological properties. However, its lower concentration in plants compared to polydatin limits its application. In this study, the polydatin-β-d-glucosidase (PBG) that hydrolyzes the β-d-glucosyl residue of polydatin with release of resveratrol was purified to homogeneity and characterized. RESULTS: The molecular weight of PBG was estimated to be 125 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 128 kDa by size-exclusion chromatography- multi-angle laser light scattering/ultraviolet/refractive index. The optimal PBG activity was observed at 70 °C and pH 4.5. The enzyme showed around 50% stability at 60 °C for 12 h and residual activity was over 80% at pH 3.0-5.0. Ca(2+) , Mg(2+) , Mn(2+) , Zn(2+) , Ba(2+) , Ni(2+) , Co(2+) and Cu(2+) ions had no significant effect on the enzyme activity. The PBG presented higher affinity to polydatin (Km = 0.74 mmol L(-1) ) than p-nitrophenyl-β-d-glucopyranoside (Km = 2.9 mmol L(-1) ) and cellobiose (Km = 8.9 mmol L(-1) ). CONCLUSION: With this enzyme, nearly all polydatin in P. cuspidatum was converted to resveratrol. Although several β-D-glucosidases (BGLs) have been obtained from other sources, PBG is distinguished from other BGLs by its outstanding thermal stability and high catalytic efficiency.