Ripening of cheese: oxidation-reduction potential and calcium phosphate.

Rennet-coagulated cheeses are ripened for periods varying from two weeks to two or more years during which the flavour and texture characteristics of the variety develop. Microbial changes during ripening include a decline in starter organisms and an increase in numbers of adventitious non-starter bacteria and, often, the development of a desirable bacterial or fungal secondary flora. Biochemical changes during ripening have been studied in considerable detail and include lipolysis and proteolysis, together with the metabolism of residual lactose, and of lactate and citrate. Lipolysis and proteolysis result ultimately in the liberation of fatty acids and amino acids, respectively, which may be metabolised to a range of volatile flavour compounds. In particular, amino acid catabolism is of considerable importance to flavour development in cheddar cheese. The effects of a number of parameters including pH, moisture, NaCl and temperature on the rate of ripening have been studied thoroughly. Oxidation-reduction (redox) potential is another fundamental physicochemical parameter that has been shown to affect the rate of formation of a number of volatile flavour compounds in vitro. Methods have been developed to monitor redox potential during cheese manufacture and ripening, and avenues are being explored to alter ripening by controlling this parameter which has heretofore been largely ignored. In addition to the production of flavour compounds, cheese ripening usually involves considerable changes to its texture due to changes to moisture, cleavage of the casein matrix of the cheese by proteolysis and alteration to the calcium equilibrium. Recent work has shown that in cheeses such as cheddar, changes to the equilibrium between casein-bound and soluble calcium phosphate affect texture development which can be modified by alteration of this equilibrium. Aust. J. Dairy Technol. 65, 178-184