DIVISION V 

 MICROBIOLOGY OF FOODS 



CHAPTER I* 



DESICCATION, EVAPORATION, AND DRYING OF FOODS 

 AGENCIES THAT BRING ABOUT CHANGES IN DRIED FOODS 



Food materials are derived from plant and animal tissues. The 

 agencies which may bring about their deterioration are those 

 initially present in the raw food, and those introduced later in the 

 process of handling. These agencies are the enzymes produced by the 

 cells constituting the food material, and the bacteria, yeasts, and molds, 

 with their enzymes, which may be introduced later. 



Enzymes are normally present in foodstuffs which have not been 

 subjected to heating, since all living cells apparently contain enzymes 

 which may remain active for a considerable length of time after the 

 death of the cells. These enzymes are usually termed autolytic, that 

 is, they digest the cells or parts of cells which produce them. They 

 are active in bringing about deterioration of certain types of foods. 

 These autolytic enzymes are of many kinds. Some of them attack 

 carbohydrates, some fats, others proteins, and still others organic 

 compounds belonging to none of these groups. They are, for example, 

 responsible for the stiffening of muscles after death (rigor mortis], 

 and later break down the tissues of the meat and bring about a so-called 

 ripening whereby it becomes more tender. They may in some instances 

 produce rancidity in food products by splitting of the fat. It is self- 

 evident, therefore, that if food is to be preserved by drying, the enzymes 

 capable of bringing about detrimental changes must either be inhibited 

 in their action or be destroyed by heat or by some other agency. 

 In most cases the drying of a food will remove water sufficiently to 

 inhibit the action of the 'enzymes as well as to prevent the growth of 

 microorganisms. If the process of desiccation is not properly carried 



* Prepared by R. E. Buchanan. 



