526 



TJ. S. BUREAU OP FISHERIES 



INTERNAL CHANGES IN FISH IN STORAGE 



Reuter, in the German work already referred to, observed changes 

 in the consistency of fish flesh that are progressive in prolonged 

 storage. These changes occur in fish frozen by any method. Imme- 

 diately after rapid freezing and defrosting the tissues of haddock, 

 for example, resemble those of fresh fish so closely that one can 

 scarcely distinguish the difference, but in storage they begin to show 

 changes after a time. Reuter's observations are shown by the fol- 

 lowing scheme: 



Term of 

 storage 



24 hours 

 18days_ 

 103 days 

 149 days 



Consistency of tissues after defrosting 



Firm as fresh muscle. Gelatinous con- 

 sistency when rubbed or squeezed 

 between fingers. 



Muscle still tenacious, viscous, and 

 gelatinous, though slightly less than 

 in above. 



Muscle much less gelatinous and vis- 

 cous; also dryer than preceding. 



No gelatinous property; fibers crum- 

 bly and dry. 



Tendency of juice to exude from fish spontaneousl y 

 after defrosting 



Cut surfaces dry; free outflow of juice at a mini- 

 mum; on pressure almost none could be squeezed 

 out. 



Cut surfaces dry; small drops of tissue juice flows 

 out spontaneously; on pressure the tissue juice 

 runs out in moderate abundance. 



Juice runs out spontaneously a little more freely 

 than in the preceding; on pressure it runs out 

 very freely, leaving the muscle fibers dry. 



Cut surface moist; spontaneous outflow of tissue 

 juice not more considerable than after 18 or 103 

 days 8 storage, but on pressure the juice continu- 

 ously exudes as if out of a sponge, so that the 

 muscle fibers remain a friable and plastic mass. 



In 1922 19 the present writer suggested, on theoretical grounds, 

 that it was possible that fish containing only minute ice crystals im- 

 mediately after freezing might contain larger ones after a period of 

 storage. There was reason to believe that, because of fluctuations in 

 temperature in storage, the larger crystals might grow at the expense 

 of the smaller ones. The Japanese investigators Ogura and Fuji- 

 kawa 20 report in a recent publication that this is true, though they 

 do not give, in the English summary (the publication itself is in 

 Japanese), the nature of their observations, nor do they indicate the 

 extent of growth of the crystals. The writer can state from his own 

 observations, however, that the change is not great, for rapidly 

 frozen fish after a period of storage do not, on close visual examina- 

 tion but without a microscope, show any noticeable crystallization. 

 The Japanese observers also state that, although the ice crystals in 

 the tissues were very small, the muscle cells invariably suffered some 

 damage. " For instance, if a slice of frozen flesh is cut off and im- 

 mersed in cold water, the cell contents will soon dissolve out into the 

 water, leaving the stroma substance something like cotton fiber. 

 This was not the case with the flesh which was not frozen. By this 

 means the fresh can easily be distinguished from the frozen flesh." 



ACQUISITION OF UNDESIRABLE ODORS 



Not only may fish in cold-storage rooms lose some of their natural 

 flavor and odor, but they may also acquire foreign odors and flavors. 



19 H. P. Taylor, " Brine Freezing of Fish." U. S. Bureau of Fisheries Economic Cir- 

 cular No. 54. Washington, 1922. 



20 Z. Ogura and K. Fujikawa, " On the refrigeration and preservation of fish." Bul- 

 letin of the Government Fishery Experimental Station of Chosen, No. 1, 1925, 162 pp. 

 (Japanese abstract in English, 8 pp.) Fusan. 



