An α-L-rhamnosidase from Aspergillus awamori MTCC-2879 and its role in debittering of orange juice

The extracellular -l-rhamnosidase has been purified by growing a new fungal strain Aspergillus awamori MTCC-2879 in the liquid culture growth medium containing orange peel. The purification procedure involved ultrafiltration using PM-10 membrane and anion-exchange chromatography on diethyl amino ethyl cellulose. The purified enzyme gave single protein band in SDS-PAGE analysis corresponding to molecular mass 75.0kDa. The native PAGE analysis of the purified enzyme also gave a single protein band, confirming the purity of the enzyme. The Km and Vmax values of the enzyme for p-nitrophenyl--l-rhamnopyranoside were 0.62mm and 27.06molemin1mg1, respectively, yielding kcat and kcat/km values 39.90s1 and 54.70mm1s1, respectively. The enzyme had an optimum pH of 7.0 and optimum temperature of 60 degrees C. The activation energy for the thermal denaturation of the enzyme was 35.65kJ1mol1K1. The purified enzyme can be used for specifically cleaving terminal -l-rhamnose from the natural glycosides, thereby contributing to the preparation of pharmaceutically important compounds like prunin and l-rhamnose.