Peptidase able to cleave azocasein and the milk substrates beta-casein and Na-caseinate. Can withstand UHT processing of milk, and is able to spoil UHT milk over the storage period. Binds 8 Ca(2+) ions per subunit. Binds 1 zinc ion per subunit. Is completely inhibited by the metal cation chelators 1,10-phenanthroline and EDTA, but PMSF, pepstatin A and E-64 have no effect on activity. Optimum pH is 8. Optimum temperature is 40 degrees Celsius. At higher temperatures, the activity decreases rapidly. Shows high enzyme activity with casein as a substrate under the storage conditions of UHT milk. Is highly thermostable. Withstands general ultra-high temperature (UHT) processing (138 degrees Celsius for 18 seconds) in skim milk, with 88% of the initial enzyme activity remaining after heating. The milk matrix has a protective effect on the enzyme activity during the thermal process. Belongs to the peptidase M10B family.