PRODUCTION AND CHARACTERIZATION OF AN ASPERGILLUS-TERREUS ALPHA-L-RHAMNOSIDASE OF ENOLOGICAL INTEREST

Conditions for maximal batch culture production of extracellular alpha -L-rhamnosidase by Aspergillus terreus have been investigated. Product ion of the enzyme appeared to be inducible by rhamnose and rutin, reac hing a maximal level after an incubation period of 162 h when the fung us was grown at 37 degrees C on either of these compounds as the carbo n source and on ammonium phosphate as the nitrogen source. Nonionic su rfactants did not enhance alpha-L-rhamnosidase secretion. Under optima l conditions, A. terreus produced only one alpha-L-rhamnosidase of app roximate molecular weight 90 kDa (SDS-PAGE) and isoelectric point of 4 .6. On p-nitrophenyl-alpha-L-rhamnopyranoside as substrate, the enzyme showed pH and temperature optima of 6-8 and 45-50 degrees C, respecti vely. Neither divalent cations nor ethylenediaminetetraacetate (EDTA) inhibited or stimulated enzyme activity. The enzyme was active at the concentrations of glucose found in must or of ethanol in wine.