Abstract:
Subject description: In the cheese industry, aspartyl proteases are used as a coagulating agent
and rennet was the first to be used. It is an enzyme extracted from the stomach of young ruminants.
Indeed, it is relatively expensive and faces the constraint of sacrificing these animals. This situation has
given impetus to research in order to replace this clotting agent with other less expensive proteases such
as microbial one.
Objectives: An acid protease produced by a fungal species isolated from an extreme
environment, a thermal soil in the region of Teleghma (Mila), is studied as a source of enzymes to be
used in cheese making.
Methods: Phenotypic and molecular identification showed that it is Aspergillus niveus. This
strain of fungus exhibited significant proteolytic activity on milk agar. A fermentation is carried out on
a liquid medium based on wheat bran enriched with the composition gram per liter 5g of (NH4) 2SO4;
2g of KH2PO4; 1g of K2HPO4 and 0.5g MgSO4, at 30°C and pH 6 with stirring at 150rpm/min) . After
7 days of incubation, the partially purified enzymatic extract is recovered by simple filtration followed
by fractionated precipitation with ammonium sulphate.
Results and discussion: The partial purification shows a proteolytic activity of 2598UI with a
coagulant activity of 0.221 UP/ml under standard conditions. This activity was strongly dependent on
the pH and temperature of the milk; it showed optimal milk coagulation at pH 5 and 60°C. The RS
rennet strength of this extract increased hyperbolically with increasing calcium concentrations and the
concentration was saturated at 50 mM. Indeed, a concentration of 50mM NaCl is accompanied by a
decrease in coagulant activity.
Conclusion: these results are encouraging; the use of a cheap and available substrate such as
wheat bran saves the cost price of the production of a milk coagulating protease on an industrial scale
