Milk-clotting properties and specific hydrolysis of caseins of the acid protease extracted from Scolymus maculatus flowers

Abstract

A milk-clotting acid protease was extracted from the flowers of an Asteraceae; a widespread plant traditionally used in Algeria, Scolymus maculatus. The enzyme was purified 40 fold using ammonium sulfate fractionation followed by exclusion chromatography. The estimation of the molecular mass of the protease by SDS-PAGE electrophoresis gave a weight of 45 kDa and Zymogram analysis revealed only one proteolytic band. The enzyme inhibition at 99% by pepstatin-A 5 mM proved that it is an aspartic proteinase; EDTA and iodoacetamide had no effect. The milk coagulation activity of this protease was optimal at pH 5 and 60°C, the rennet strength (RS) of the extract increased with calcium concentrations and was saturated at 50 mM. The enzyme exhibited hydrolytic activity toward κ-casein, α s -and β-casein. These results indicated that Scolymus maculatus protease has technological effects similar to that of the chymosin; the enzyme could be used in cheese making as a substitute for rennet