Proteolysis of ovine and caprine caseins in solution by enzymatic extracts from flowers of Cynara cardunculus

Primary proteolysis of ovine and caprine Na-caseinate at 30°C in phosphate buffer at pH 6.5 or 5.5 in the absence of NaCl and at pH 5.2 with 5% (w/v) NaCl by cardosins in aqueous extracts of Cynara cardunculus flowers was investigated using urea-polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography. Caprine caseinate underwent more extensive degradation then ovine caseinate under the same conditions (pH 6.5 and pH 5.5); proteolysis of β- and α(s)-caseins in ovine and, to a lesser extent, in caprine caseinates was reduced in the presence of 5% (w/v) NaCl. Peptide profiles of the pH 4.6-soluble extract had different patterns throughout ripening arising from the different specificity of cardosins toward ovine and caprine Na-caseinates. The major cleavage sites in ovine (caprine) caseinate were Phe105-Met106 (Lys116-Thr117) for κ-casein, Leu127-Thr128 and Leu190-Tyr191 (Glu100-Thr101, Leu127-Thr128, Leu136-Pro137 and Leu190-Tyr191) for β-casein, Phe₂₃-Val₂₄ (Phe₂₃-Val₂₄, Trp164-Tyr165 and Tyr173-Thr174) for α(s1)-casein and Phe88-Tyr89 (Ser9-Ser10, Phe88-Tyr89 and Tyr179-Leu180) for α(s2)-casein.