Cheese is a complex microbial ecosystem containing microorganisms that are either deliberately added or that enter milk, curd or cheese as contaminants. From a technological point of view, the microbiota of cheese could be classified according to the following scheme [1,2]: (i) (primary) starter cultures, composed of lactic acid bacteria (LAB) that “start” fermentation and, consequently, the acidification of milk and curd; (ii) (secondary) adjunct cultures, comprising different species of bacteria, yeasts and molds, which are intentionally added to the milk, the curd, the surface of the cheese or the interior of the previously punctured mass in the manufacture of blue cheeses, with the aim of participating in cheese ripening and the development of sensory characteristics; and (iii) (secondary) adventitious microbiota, made up of microorganisms that spontaneously contaminate milk or cheese at any of the production stages and that contribute, similarly to adjunct cultures, to the development of the characteristic appearance, texture and flavor of the different cheese varieties, yet which are occasionally responsible for defects and off-flavors.
Cheeses made from raw milk (especially from sheep or goats, or from cattle reared using extensive methods) are generally assumed to have a more intense and rich flavor than cheeses made from pasteurized or microfiltered milk. The native microbiota present in raw milk seems to be primarily responsible for the typical sensory properties and flavor development of these products. Nevertheless, it must be taken into account that the microbial diversity of raw milk (particularly raw cow’s milk) has been seriously threatened in industrialized countries as a consequence of the implementation of strict hygienic conditions on farms and during milking, as well as when stored at low temperatures. In certain current productions of traditional raw cow’s milk cheeses, the presence of adventitious bacteria such as enterococci has decreased dramatically compared to those analyzed several decades ago, and some flavor attributes are most likely being lost [3].
In order to control cheese ripening, the first and most focused approach would lie in the isolation and selection of autochthonous microbial cultures, returning them to cheesemakers for the production of the different cheese varieties. This choice would allow for the partial restoration of the flavor in productions where the use of raw milk is restricted, or where raw milk has undergone an improvement in its microbiological quality and a consequent modification of its “traditional” microbiota. The use of selected adjunct microbial cultures may enhance the typicality of the Protected Designation of Origin (PDO) cheeses, resulting in a closer sensory quality to that of traditional products [4].
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