Purification and characterization of Aspergillus niger α-L-rhamnosidase for the biotransformation of naringin to prunin

An α-L-rhamnosidase, which was extracted from the fermented broth of Aspergillus nigerwas purified, characterized and confirmed via biotransformation of naringin to prunin. After being purified to homogeneity by ammonium sulphate fractionation and chromatography on diethylaminoethanol (DEAE) Sepharose and Sephacryl S-200 HR columns, the enzyme was determined by the exclusive gel chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE) to have a molecular weight of approximately 87 kDa. Its optimal pH and stable pH values were within the range of 4.5 to 5 and 3.5 to 7.5, respectively while its optimal temperature was in 50 to 60°C. In addition, the enzyme was strongly inhibited by Fe2+, Fe3+, Zn2+, Al3+, Mn2+, Cu2+, Ag+, Hg2+ ions and sodium dodecyl sulfate (SDS) and slightly activated by K+ and Ba2+ ions. Its Kmtowards naringin was 0.27 mM and the Vmax was 9805.15 U/mg. The enzyme could efficiently convert naringin to prunin with a transforming rate above 97%. These results indicate that the α-L-rhamnosidase separated from A. niger could be a promising candidate for its commercial application in food and pharmaceutical industries.   Key words: Aspergillus niger, α-L-rhamnosidase, naringinase, naringin, pruning, transformation