pH stability and influence of salts on activity of a milk-clotting enzyme from Solanum dubium seeds and its enzymatic action on bovine caseins

In this study we investigated the pH stability and effect of salts on the activity of a partially purified enzyme from Solanum dubium seeds as well as its hydrolytic power on caseins and caseins components. The seeds of S. dubium were blended and extracted using 50 g/L NaCl in 50 mmol/L acetate buffer, pH 5.0. The enzyme was then partially purified using ammonium sulfate. The results obtained showed that both NaCl and CaCl2 enhanced the proteolytic activity of the enzyme and the enhancement was found to be significant when NaCl was used. Moreover, the stimulatory effect was found to be concentration dependent. The proteolysis of bovine whole casein and casein subunits by the enzyme during incubation was studied by SDS–PAGE. The results obtained revealed that both κ-casein and β-casein are the most susceptible to hydrolysis than α-casein. The three main casein components α-, β-, and κ-caseins were sensitive to the action of the enzyme and the order of hydrolysis obtained was κ- casein, β- casein, and α- caseins.