Novel milk-clotting enzyme from Bacillus stearothermophilus as a coagulant in UF-white soft cheese

The Crude enzymatic extract produced by Bacillus stearothermophilus exhibited high milk-clotting activity (MCA). Optimized medium and conditions increased the enzyme production to 189.68%. Moreover, dissolving skim milk in acetate buffer and in acetate buffer containing CaCl2 increased the activity to 353.01% and 394.01%, respectively. MCA was increased to 462.76% when assayed at higher temperature (60 °C). Mn+2 and Ca+2 ions stimulated MCA to 642.11% and 134.92%, respectively. In the presence of 0.1 M NaCl the activity was increased to 128.34%, however, at 0.8 M the activity was decreased to 38.40%. MCE showed excellent thermal and pH stability by retaining all of its activity after incubation at 40 °C for 60 min and at pH 4.0 for 90 min. Furthermore, milk-clotting enzyme (MCE) retained its complete activity when stored at −18 °C and 4 °C for 40 and 30 day, respectively. UF-white soft cheese chemical characteristics were similar of both B. stearothermophilus MCE and other commercial coagulants. Moreover, cohesiveness, springiness, gumminess and chewiness were similar of cheese made with all tested coagulants. The flavor of B. stearothermophilus cheese was similar with other commercial coagulants during all storage period. Also, the total score of organoleptic properties of cheeses made by B. stearothermophilus coagulant were lower than other commercial coagulants during all storage period. Thus this novel coagulant (26 ml/l milk) could be used to produce acceptable UF-white soft cheese.