Invited review: Milk-clotting enzymes of microbial origin and their role in cheesemaking—A review

There is a growing number of scientific reports on the production and extraction of new alternatives for milk-clotting enzymes (MCE), as a result of the growing demand for cheese and the limited availability of rennet. This article reviews the different types of microbial MCE, sources of their origin, and the effects of different factors on their milk clotting activity (MCA) and proteolytic activity (PA). The influence of microbial enzymes on the final product quality and production efficiency are considered. The most desirable characteristic of the enzyme applied in cheese production is a high ratio of MCA to PA, which indicates that the enzyme is more effective in coagulation than proteolysis. The quality of MCE and thus its MCA, PA, and the ratio of MCA to PA, depends on the method for obtaining enzymes (i.e., cultivation temperature, initial pH of medium, nitrogen and carbon sources, and NaCl concentration). It is crucial to estimate the proper amount of the enzyme added during cheese manufacture. Insufficient addition of rennet substitutes leads to a loose cheese structure and low cheese yield. In turn, a large amount of rennet substitutes results in the development of strong bitterness during cheese ripening. The use of enzymes produced by microorganisms allows the production of cheeses with desired organoleptic properties and increases the flexibility of production processes in the dairy industry.