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

Summary

The extracellular α-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 75.0 kDa. The native PAGE analysis of the purified enzyme also gave a single protein band, confirming the purity of the enzyme. The K_m and V_max values of the enzyme for p-nitrophenyl-α-l-rhamnopyranoside were 0.62 mm and 27.06 μmole min⁻¹ mg⁻¹, respectively, yielding k_cat and k_cat/k_m values 39.90 s⁻¹ and 54.70 mm⁻¹ s⁻¹, respectively. The enzyme had an optimum pH of 7.0 and optimum temperature of 60 °C. The activation energy for the thermal denaturation of the enzyme was 35.65 kJ⁻¹ mol⁻¹ K⁻¹. The purified enzyme can be used for specifically cleaving terminal α-l-rhamnose from the natural glycosides, thereby contributing to the preparation of pharmaceutically important compounds like prunin and l-rhamnose.