Methods for the Thermal Stabilization of α-L-Rhamnosidase and Inactivation of β-Glucosidase in the Naringinase Complex from Aspergillus niger

Naringinase is an enzyme complex composed of α-L-rhamnosidase and β-D-glucosidase, capable of deglycosylating flavonoids such as hesperidin. α-L-rhamnosidase converts hesperidin into rhamnose and hesperetin 7-O-glucoside (Hes-7-G), while β-D-glucosidase further hydrolyses Hes-7-G to hesperetin. Selective inactivation of β-D-glucosidase enables accumulation of Hes-7-G, a compound with higher water solubility and bioavailability than hesperidin or hesperetin, making it valuable for food and biotechnological applications. This study aimed to identify conditions allowing selective inhibition of β-D-glucosidase while preserving α-L-rhamnosidase activity for efficient Hes-7-G production. The effects of pH, temperature, and incubation time were investigated, together with the influence of polyols and sugars, including inositol, sucrose, glycerol, xylose, erythritol, xylitol, and sorbitol, on α-L-rhamnosidase thermostability. Among the tested additives, erythritol significantly improved α-L-rhamnosidase thermostability. The highest selectivity was achieved by incubating the enzyme in 1.4 M erythritol at 70 °C for 10 min, resulting in ~5% residual β-D-glucosidase activity and 50% α-L-rhamnosidase activity. Under these conditions, α-L-rhamnosidase activity exceeded β-D-glucosidase activity by more than 60-fold. Selective thermal inactivation of β-D-glucosidase in the presence of erythritol provides an effective strategy for producing Hes-7-G from hesperidin and may enhance flavonoid bioavailability for industrial applications.