P L H McSweeney

The pH of cheese is a very important physicochemical parameter which affects the texture of cheese, its flavour and microbiological safety [17]. The pH of cheese is determined by the combined effects of acidification by the starter organisms (and deacidification during ripening by secondary organisms in certain varieties) and the ability of the cheese curd to resist changes in pH, i.e. its buffering capacity. The buffering capacity of milk is low near its natural pH (6.7) and increases to a maximum at about pH 5.1. Thus, assuming a steady rate of acid development by the starter, the pH of milk decreases rapidly initially and later slows down. Since the composition of cheese is quite different from that of milk, the pH at which maximum buffering occurs is also different; Cheddar and Emmental cheeses have maximum buffering capacities at ~pH 4.8.

The main components in cheese that buffer against changes in pH are the caseins and their degradation products, inorganic phosphate and organic acids (e.g. lactate, citrate, propionate, acetate and butyrate). The levels of these constituents in cheese vary with the composition of the milk and by the treatments of the curd that affect syneresis [34] and moisture levels and pH at whey drainage. The buffering capacity of cheese may also change during ripening owing to the production of CO2 or organic acids, precipitation of calcium phosphate (as occurs at the surface of Camembert-type cheese), formation of calcium carbonate on the cheese surface (e.g. in hard cheeses), degradation of lactate and proteolysis of the caseins or their dephosphorylation.

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