Résumé:
The aim of this present study is pepsin extraction from forestomach of chicken for use as milk coagulant. Proteolytic and clotting properties of pepsin and enzyme activity during conservation of the pepsin extract are studied. The chicken pepsin is extracted by maceration of the forestomach tissues in a saline solution (3% NaCl). Milk clotting activity of this enzyme is assessed by milk clotting time. The effect of pH, temperature and enzyme concentration abate clotting activity are studied. Proteolytic activity is estimated by titration of the non protein nitrogen (NPN) released during milk clotting. Four methods were studied for pepsin extract conservation: refrigeration, freezing (-18°C), vacuum drying (45°C, 200mbar) and freeze-drying. Milk clotting activity of clarified chicken pepsin extract obtained is 8.36 MCAU/ml. The strength of this extract is 2579 (litre of clotted milk per litre of extract). Decease milk pH between 7.0-5.8 is favourable for milk clotting activity of both chicken pepsin and trade calf rennet. The chicken pepsin is more sensitive to pH shift. Maxima milk clotting activities of chicken pepsin extract and trade calf rennet are observed at 55 and 50°C, respectively. The chicken pepsin is more temperature sensitive than calf rennet. A good inverse proportionality relation between the amount of enzyme and clotting time is obtained for both enzymes. The rate of NPN released during the clotting of milk with pepsin is less than that released with calf rennet. The NPN released by pepsin stays constant after 20 min of action which indicates limited specific proteolytic activity. For clarified and concentrated pepsin extract, freezing is more preservative of milk clotting activity than refrigeration. More than 90 % of initial milk clotting activity of pepsin is recovered after vacuum drying or freeze-drying. After 56 days of conservation the freeze-dried and vacuum dried pepsin pepsins keep 80.25 and 75.74% of their initial milk clotting activity, respectively.
