CHAPTER 27 



Bacteriological and Chemical Basis 

 for Deteriorative Changes 



John Liston, Maurice E. Stansby, and H. S. Olcott 



From the moment fish is taken from the water a series of deteriorative 

 changes start to occur which eventually will render the fish unmarketable. 

 These changes occur relatively rapidly, such that fish is probably the 

 most perishable of all flesh foods. 



These changes occur as either the result of microbiological action or 

 can be classified as being some form of more or less pure chemical change. 

 In most cases, the deteriorative changes resulting from microbiological 

 action are the most extensive. Hence a large part of this chapter is 

 devoted to bacteriological considerations. 



Proteins, the most important food component of fish, undergo various 

 chemical changes and these will be described. In some special cases, 

 notably in cold storage of frozen fish, largely chemical alteration in the 

 lipids is involved so that a consideration of such changes, especially 

 those involving oxidation, is included. 



Microbiological Changes 



Bacterial Populations on the Living Fish. More or less large populations 

 of bacteria are constantly present on the external surfaces of all marine 

 animals. In the case of free-swimming fish, the numbers of bacteria on the 

 skin range from 10^ to 10^ per square centimeter, on the gills from 10^ to 

 10^ per gram, and in the intestine from very few in nonfeeding fish to 

 10^ or more per gram in feeding fish. Less information is available for 



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