CHAPTER XIV 



KELATIONSHIPS OF MICROORGANISMS TO THE 

 PRESERVATION OF FOOD 



Agencies which Bring about Deterioration of Foods. 



The agencies which bring about deterioration in foods and 

 food products may be grouped under two general headings : 

 the intrinsic, including those which are normally present 

 in the food itself and have not been derived from outside 

 influences ; and second, those which may be termed extrinsic, 

 that is, those which enter the food at some time during the 

 process of preparation or ripening. To the first group 

 belong the so-called autolytic enzymes. In certain fatty 

 foods, for example, there may be hydrolyzing enzymes 

 which will bring about rancidity. In fruits and certain 

 vegetables the enzymes which normally bring about ripen- 

 ing may bring about a condition of overripeness. Certain 

 of the oxidizing enzymes, such as those present in fruits, 

 may produce discoloration. Of the extrinsic agencies 

 capable of bringing about food deterioration, there are the 

 bacteria, the yeasts and the molds together with the 

 enzymes which they produce. 



In general the bacteria thrive best in nitrogenous foods 

 containing considerable proportion of water and not too 

 much acid; they grow best in a medium which is nearly 

 neutral. The yeasts, for the most part, grow best in a 

 medium rich in carbohydrates, particularly in the ferment- 

 able sugars, and preferably in the presence of some acid. 

 Like the bacteria, they prefer a considerable amount of 

 moisture. The molds will grow in media somewhat drier 

 and of almost any type. Certain molds will grow on foods 



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