284 MARINE PRODUCTS OF COMMERCE 



compounds as are produced during autolysis, such as polypeptides and amino 

 acids. These are only intermediate products and are later decomposed into a wide 

 variety of substances, including ammonia, amines, indole, hydrogen sulfide, and 

 skatol, many of which have disagreeable odors. Most of the end products of 

 bacterial decomposition of fish are basic, so that a rise in the pH is observed. 

 However, when bacterial decomposition occurs at low temperatures, as when the 

 fish is packed in ice, the principal products are the intermediate ones. 



Stansby and Lemon (1933) have indicated that, although fish decomposition 

 is usually classified as bacterial or autolytic, a more satisfactory test for freshness 

 is based upon the type of products formed: (1) primary changes, which lead 

 to the formation of amino acids from protein or to any intermediate product such 

 as polypeptides and peptones; (2) secondary changes, including those which lead 

 to the formation of such products as amines, indole, hydrogen sulfide, and skatol 

 which detract from the value of the fish and usually contribute disagreeable 

 flavors or odors. Although the primary changes which occur in the proteins of 

 fish flesh do not cause the formation of compounds having foul odor and flavor, 

 other objectionable changes do occur. 



As the protein molecule hydrolyzes, the fish becomes softer. In extreme cases 

 juices, which contain dissolved protein, amino acids, and minerals, run from the 

 fish. Furthermore, a fish in which primary changes have occurred is much more 

 readily decomposed into secondary decomposition products when exposed to high 

 temperatures and the action of bacteria. The secondary decomposition is gen- 

 erally considered to be the result of bacterial action and the end products are 

 chiefly basic. This type of decomposition is usually considered as fish spoilage 

 and renders the fish inedible. 



When freshly caught fish are packed in ice, primary changes are the chief 

 types of degradation occurring for the first few weeks. If the fish have been packed 

 in ice for longer than a few days and are then removed from the ice, secondary 

 decomposition sets in very rapidly and true spoilage occurs. 



Nickerson, Goldblith, and Proctor (1950) have recently obtained some very 

 valuable data concerning the bacterial and enzymatic changes which occur during 

 the holding of mackerel under various conditions of temperature and sterility, as 

 well as similar facts concerning the changes occurring during the refrigerated 

 storage of haddock and haddock fillets (Proctor, Nickerson and Goldblith, 1950). 

 They found that trimethylamine and volatfle acids increase in haddock fillets 

 stored under refrigeration only when bacteria are present in significant nimibers. 

 Increases in trimethylamine and volatile acids seem to be correlated with the 

 levels of the microorganisms present. Autolysis was not found to be an important 

 factor in spoilage. Trimethylamine and volatfle acids produced by the action of 

 bacteria on the surface tissues of eviscerated haddock held in crushed ice effuse 

 into the flesh and accumulate in the deeper tissues. They also noted that iced 

 whole, non-eviscerated fish do not spofl as quickly as eviscerated fish simflarly 

 refrigerated. 



A number of tests for the degree of freshness of fish have been proposed. 

 Almy (1925) has suggested one based on the presence of hydrogen sulfide as an 

 indication of decomposition. The Tillmans and Otto (1927) test involves the 

 determination of ammonia. Other tests have been described by Fellers, Shostrom, 

 and Clark (1924), Clough (1922)_, Tressler (1919), Tillmans, Hirsch, and 



