Ripening temperature
Temperature is one of the few parameters the cheesemaker can manipulate to control microbial development during the ripening stage of cheese production. The microorganisms involved in cheese manufacture and ripening are either mesophilic or thermophilic, having temperature optima between 30 and 42 0C. The temperature at which cheese is ripened is a compromise between the need to promote ripening reactions and control growth of the desirable secondary flora, and the need to prevent the propagation of potential spoilage and pathogenic bacteria. Most cheeses are ripened at temperatures in the range 6-15 0C; exceptions are Swiss-type cheeses which undergo a period at 22-25 0C to promote the growth of PAB. Higher temperatures promote accelerated ripening, but the changes to body and flavour are often detrimental.
The final factor to consider with regard to the growth of microorganisms in cheese is availability of nutrients. Cheese has a relative abundance of protein, amino acids and fat and these are not limiting factors for the growth of most microorganisms. However, the carbohydrate content of cheese is relatively low. Residual lactose is present in cheese following manufacture but this is rapidly depleted in the early days of ripening and is often totally absent during the time in which many of the secondary and NSLAB flora are actively growing. Citrate is present in small amounts (-8mmolkg—1) but is not considered to be a significant energy source for microbial growth in cheese. Lactate, which is the major end product resulting from lactate fermentation by the starter bacteria, is present in cheese and is metabolised by some microbial flora including PAB, mould and yeasts. The growth of NSLAB [56] has received particular attention as significant growth continues following depletion of lactose. Recent research has demonstrated that many possess glycoside hydrolases and can utilise sugars derived from the glycomacropeptide of casein and the glycoproteins of the milk fat globule membrane.
In summary, while a wide diversity of microorganisms have the capacity to grow in cheese, the manufacturing process greatly restricts most either directly, by preventing entry or inactivation on entry, or indirectly through the creation of unfavourable environmental conditions in the cheese.
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