344 FOOD SCIENCE APPLICATIONS 



than does the edible portion. These differences may be quite pronounced 

 (see Table 26.7). 



Table 26.7. Proximate Composition of Whole Fish, 



Edible Flesh and Trimmings of Dover "Sole" 



{Microstomus pacificus) 



Major Components of Fish 



Water. Water is the principal component of fish, amounting to as much 

 as 80 per cent of the edible flesh. Usually there is an inverse relationship 

 between oil and water content of fish muscle, such that the sum of the two 

 is close to 80 per cent. 



The water in fish does not freeze at 32°F. Rather, it starts to freeze at 

 about 30.5°F. As the temperature of the fish is lowered, the amount 

 frozen at successively lower temperatures increases. Even at 22°F only 

 about 90 per cent of the water is frozen. Substantially all is frozen at 

 about -30°F. 



The moisture in fish tissue is held tightly by colloidal as well as chemical 

 forces so that fresh fish subjected to high pressures do not release much 

 of it. This retention of water by the fish can be measured by centrifuging 

 the fish and determining the amount of fluid which separates after apply- 

 ing a stipulated centrifugal force for a stated period of time. This water 

 retentivity of fish flesh is greatest in freshly caught, untreated fish. Either 

 storage at ice temperatures or freezing of the flesh results in reduced 

 water retentivity. 



Protein. Protein, although second to water in quantity of the com- 

 ponents of fish, ranging from 6 to 28 per cent but usually amounting to 

 18 to 20 per cent, is the most important component of fish. 



Proteins are very large molecules which can be broken down to alpha- 

 amino acids by treatment with acids or enzymes. The principal amino 

 acids are shown in Table 26.8 with their abbreviations and content in 

 various fish proteins. Those capitalized are essential for the nutrition of 

 man. 



The assortment of amino acids, the various orders in which they may 

 be- combined and the manifold possibilities of distribution in space (as 

 long threads or globules or any intermediate form) account for the al- 

 most infinite variety of functions which proteins perform. In fish the skin 



