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In this study, we found the addition of sorbitol could improve the thermostability of α‐l‐rhamnosidase from Aspergillus niger. When α‐l‐rhamnosidase with sorbitol was heat‐treated at 60°C, 65°C, and 70°C, the half‐life t1/2 increased by 28‐, 18‐, and 9‐fold, respectively. Inactivation thermodynamic analysis showed that both Ea and ΔG≠ of α‐l‐rhamnosidase increased. Through the response surface methodology (RSM) analysis, the higher hesperidin conversion (63.26%) by α‐l‐rhamnosidase was attained with 0.7 M sorbitol at 60°C and pH 4.5 for 10 min. Furthermore, hesperidin could be completely hydrolyzed after 10 hr of reaction. Overall, the results indicated that the addition of sorbitol improved the thermostability of α‐l‐rhamnosidase and increased the enzymatic conversion of hesperidin to hesperetin‐7‐O‐glucoside (HMG). It also provided a simple and efficient way to increase enzymatic conversion of other valuable flavonoid monomers due to the broad substrate specificities of α‐l‐rhamnosidase from A. niger. Practical applications: Hesperetin‐7‐O‐glucoside (HMG), a derhamnosylation product of hesperidin, is considered as a synthetic precursor for novel and efficient sweeteners and is important in food, functional food, and nutraceutical industries. Compared to chemical hydrolysis methods, the enzymatic conversion of hesperidin is milder and has the advantages of high specificity. Adding sorbitol can improve the thermostability of α‐l‐rhamnosidase and increase the enzyme efficacy against hesperidin. This study gave more evidence that adding sorbitol could improve the thermostability of enzymes and provide a better choice for improving biotransformation potency of enzymes. [ABSTRACT FROM AUTHOR]

ABSTRACT β-D-glucosidase has been purified from naringinase of Aspergillus niger to homogeneity by ammonium sulfate fractionation and chromatographies on diethylaminoethyl Sepharose, phenyl-Sepharose and Sephacryl S-200 HR, with the aid of prunin used as a specific substrate to detect the β-D-glucosidase activity by a high-performance liquid chromatography method. The molecular weight of the β-D-glucosidase was determined to about 100 kDa by exclusive gel chromatography and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis analysis. Optimal pH and stable pH range of the enzyme were 4.5-5 and 3.5-8.0, respectively. Its optimal temperature was in the range of 55-60C. The enzyme was strongly inhibited by 1 and 5 mM of Fe2+, Fe3+, Zn2+, Al3+, Mn2+, Cu2+, Ag+ and Hg2+ ions and SDS. This β-D-glucosidase had a higher specific affiliation to prunin than p-nitrophenyl-β-D-glucopyranoside. Its Km and Vmax toward prunin were 2.59 mM and 18.76 U/mg. PRACTICAL APPLICATIONS This paper mainly focused on the purification and characterization of the β-D-glucosidase from the enzyme complex naringinase, which was prepared from a fermented broth of Aspergillus niger. To our knowledge, it is the first successful attempt to purify and characterize the β-D-glucosidase from this naringinase, which is considered safe for food use. This study can help interested readers to take further insights into naringinase from A. niger and set strong base for the production and industrial applications of the β-D-glucosidase, which is useful to debitter citrus juice and produce medical ingredients. [ABSTRACT FROM AUTHOR]