COMPARATIVE EVALUATION OF Bacillus licheniformis 5A5 AND Aloe variegata MILK-CLOTTING ENZYMES

The properties of a milk clotting enzyme (MCE) produced by bacteria (Bacillus licheniformis 5A5) were investigated and compared to those of rennet extracted from a plant (Aloe variegata). Production of MCE by B. licheniformis 5A5 was better in static than in shaken cultures. Maximum activity (98.3 and 160.3 U/ml) of clotting was obtained at 75 degrees C and 80 degrees C with bacterial and plant rennet, respectively. In the absence of substrate, the clotting activity of Aloe MCE was found to be less sensitive to heat inactivation up to 80 degrees C for 75 min, retaining 63.8% of its activity, while bacterial MCE was completely inhibited. CaCl2 stimulated milk clotting activity (MCA) up to 2% and 1.5% for bacterial and plant enzymes. NaCl inhibited MCA for both enzymes, even at low concentration (1%). Plant MCE was more sensitive to NaCl at 3% concentration it retained 30.2% of its activity, whereas bacterial MCE retained 64.1%. Increasing skim milk concentration caused a significant increase in MCA up to 6% for both enzymes. Mn2+ stimulated the activity of bacterial and plant enzymes to 158.6 and 177.9%, respectively. EDTA and PMSF increased the activity of plant MCE by 34.4 and 41.1%, respectively, which is higher than those for the bacterial MCE (19.1 and 20.9%). Some natural materials activated MCE, the highest activation of bacterial MCE (128.1%) was obtained in the presence of Fenugreek (with acid extraction). However Lupine Giza 1 (with neutral extraction) gave the highest activation of plant MCE (137.9%). All extracts from Neem plant increased MCA at range from 105.6% to 136.4%. Plant MCE exhibited much better stability when stored at room temperature (25-30 degrees C) for 30 days, retaining 51.2% of its activity. Bacterial MCE was highly stabile when stored under freezing (-18 degrees C), retaining 100% of its activity after 30 days. Moreover, bacterial MCE was highly tolerant to repeated freezing and thawing without loss of activity for 8 months.