DIVISION V 

 Microbiology of Special Industries 



CHAPTER I* 

 DESICCATION, EVAPORATION, AND DRYING OF FOODS 



Factors That Bring About Changes in Dried Foods 



The factors that bring about changes in dried foods may be considered 

 under two general heads, chemical and microbial. Enzymes, although 

 the product of living cells, may represent the chemical changes, and the 

 activity of bacteria, yeasts and molds, the microbial changes. Enzymes 

 are normally present in food stuffs derived from animals or plants which 

 have, not been subjected to heating. AU living cells contain enzymes, 

 and these may remain active foj a considerable time after the death 

 of the cell. Some of these enzymes attack carbohydrates, some fats, 

 some proteins, and some other compounds. Enzymes are responsible 

 for the stiffening of the muscles after death {rigor mortis), others later 

 break down the tissues and bring about a ripening of meat whereby it 

 becomes more t^ender. Autolytic enzymes may in some instances 

 produce rancidity in food products by a splitting of the fats. Bacterial 

 enzymes are known that duplicate the action of practically all those 

 produced by higher animals and plants. Some of the changes pro- 

 duced are desirable, others undesirable, particularly if action is allowed 

 to continue for too long a time. In foods dried for preservation, it is 

 therefore important that sufficient heat be used to destroy the enzymes 

 or that enough water be removed to inhibit their activity. Ordinarily 

 the activity of enzymes will be inhibited by the removal of water 

 sufficient to prevent the growth of microorganisms. The action of 

 enzymes is characterized as reversible, that is, after a certain concen- 

 tration of enzymic products has been reached, the transformation ceases 



* Prepared by R. E. Buchanan. > 



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