518 U. S. BUREAU OF FISHERIES 



wholesomeness, well recognized by fishmongers. There is some ques- 

 tion as to whether fish are best frozen before, during, or after rigor. 15 

 Some investigators have observed that cod frozen before rigor had a 

 dry and disagreeable taste. Others have thrown doubt on this con- 

 clusion and indicated by experiments that it is possible to have fish of 

 good flavor in both cases. 



AUTOLYSIS 



As rigor subsides another change comes about, perhaps assisted by 

 the lactic acid that causes rigor. This is autolysis, or self -digestion 

 of the tissues. It is an important change that requires some expla- 

 nation. 



There are certain substances called enzymes that are capable of 

 decomposing or breaking down complex into simpler substances. A 

 familiar example of such a substance is pepsin in the stomach, which 

 breaks down the complex substance (protein) of lean meat into 

 simpler substances that dissolve in water to form liquid solutions. 

 This liquefaction of food is digestion and serves to prepare the food 

 for absorption into the blood through the intestinal wall There are 

 many such enzymes in the animal body, most of the tissues contain- 

 ing enzymes capable of liquefying or digesting them- These enzymes 

 serve an important purpose in the living animal, but upon its death 

 they set to work to soften and liquefy the tissues. This self-digestion 

 of fish substance is called autolysis. 



The products of autolysis are not unwholesome. Indeed, a certain 

 amount of autolysis or ripening, as butchers call it, is desirable in 

 red meats, for it makes them tender and juicy, and most people prefer 

 the flavor. In fish, however, autolysis, while harmless, gives rise to 

 a fishy flavor that is distinctly objectionable. Fish that have under- 

 gone autolysis are soft and flabby. Impressions made on the fish 

 with one's fingers remain when the fingers have been removed. 

 Autolysis occurs in fish after rigor has passed away. It is hastened 

 by warmth and retarded by cold. The maximum rate is at tempera- 

 tures varying with different fishes from about 65 to 81° F. Bruises 

 promote autolysis, for it has been shown that bruised or crushed meat 

 softens and digests itself much more rapidly than meat not bruised. 

 Autolysis is prevented entirely by freezing the fish solid, but it begins 

 again when the fish is defrosted. Salt in small quantities increases 

 autolysis. Slowly frozen fish autolyze more rapidly than fresh 

 fish, while rapidly frozen fish autolyze less rapidly. 16 



lB The subject is discussed by the following authors, whose works are extensive theo- 

 retical studies of scientific principles of freezing fish : W. D. Richardson and B. Scherubel, 

 " The deterioration and commercial preservation of flesh foods." Journal of the Ameri- 

 can Chemical Society, Vol. XXX, pp. 1515-1564. Easton, 1908. J. M. Bottemanne [Ed.], 

 " Verslag van de door Nederlandsche Vereeniging voor de koeltechniek ingestelde Commissie 

 voor de Vischconserveering, etc." Delft, 1915. See also, Third International Congress of 

 Refrigeration, Chicago, 1913. R. Plank, E. Ehrenbaum\ and K. Reuter, " Die Kon- 

 servierung von Fischen durch das Gefrierverfahren." 248 pp. Zentral Einkaufsgesell- 

 schaft, Berlin, 1916. See also, Stiles, footnote 45, p. 580, and Ogura and Fujikawa, foot- 

 note 20, p. 526. 



18 See Oya, Takeo, and Kiyoshi Shimada on the " Autolysis of fish muscle." I. Journal 

 of the Imperial Fisheries Institute ,Vol. XIX, No. 3, 1923. Oya, Takeo, Ei-etsu Sumi, 

 and Kiyoshi Shimada II. Ibid., Vol. XXI, 1926, pp. 49-149. Callow, E. H., "The 

 autolysis of the muscle of the cod." Biochemical Journal, Vol. XIX, 1925, pp. 1-6. 

 Cambridge. 



