Curd Protein 417 



After this reaction is completed, the curd proteid is again 

 changed into an insoluble form. The latter is in turn 

 gradually transformed in the ripening process into 

 water-soluble compounds. This last series of changes, 

 which are intimately associated with the final digesti- 

 bility and flavor of the cheese, involve the gradual 

 breaking down of the proteid substances, and the 

 formation of the so-called amides (ami do compounds). 

 It has been found that a properly ripened Cheddar or 

 Swiss cheese may contain about a third of its total 

 nitrogen in the amid form, and that 3 to 5 per cent may 

 be present as ammonia. It is to these various amides 

 and the ammonia that the cheese flavors are largely 

 due, at least, in the case of the hard cheeses. The well- 

 known influence of temperature on the rate of ripening 

 and the flavor may be explained by the differences in the 

 proportionate amounts of the various amides formed. 



We see, thus, that the ripening of cheese is not unlike 

 the putrefaction of other protein bodies. However, 

 some of the characteristic putrefaction products are 

 absent from normally ripened cheese. It is only in ex- 

 ceptional cases that such putrefaction products appear. 

 They may give rise, then, to ptomaine poisoning. While 

 the changes leading to the formation of poisonous sub- 

 stances in cheese have not yet been made clear, it is 

 assumed that these compounds are most likely to appear 

 in over-ripe or improperly ripened cheese. 



Enzymes and bacteria in the ripening of cheese. — When 

 modern methods of investigation were first brought to 

 bear on the problem of cheese-ripening, it was believed 

 that bacteria and other microorganisms were the sole 



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