FISH-LIVER OILS 503 



Extraction of Crayfish and Shark-Liver Oils 



The hver of the giayfish (dogfish) found on the Pacific Coast contains an 

 average of 15,000 U.S. P. units of vitamin A per g, while the same species on the 

 Atlantic Coast contains only 2,000 to 3,000 units of vitamin A. This accounts for 

 the fact that this species has never been sought for the vitamin A-bearing oil on the 

 Atlantic Coast. There is no satisfactory explanation for this phenomenon. 



The steaming process is used extensively on the Pacific Coast to remove oil from 

 livers containing 50 per cent oil with a vitamin A potency of 8,000 to 15,000 U.S.P. 

 units. The coarsely ground livers are placed in a tank and live steam is admitted 

 for cooking. In a few plants the cooking tank is fitted with a mechanical stirring 

 apparatus to increase the agitation of the hver particles and to facilitate a more 

 even cooking. The oil released may be separated from the water and liver residue 

 by gravity; but since most plants are equipped with a 3-phase centrifuge, this 

 method is preferred. In some plants the water phase of the material separated 

 by centrifuge is washed with low-potency vitamin A oil, such as sardine or other 

 low-potency body oil, to remove the last traces of vitamin A from the water before 

 it is discharged. 



Harrison and Hamm (1941) found that it was possible to remove 80 per cent 

 of ground dogfish-liver oil containing 5,000 U.S.P. units of vitamin A by means of 

 a basket centrifuge. However, the potency of the oil was considerably less than 

 that indicated by the assay of the livers. Upon acid digestion of the residue, these 

 workers obtained an equivalent of 13.5 per cent of the Hver oil with a potency of 

 15,200 U.S.P. units of vitamin A per g. Bailey (1941) suggested that a coagula- 

 tion of the liver protein by means of calcium chloride would release the oil. It was 

 found that this method required two stages to remove completely the oil and 

 vitamin A content of the livers. 



Crayfish (dogfish) which had been initially cooked in a retort at steam pres- 

 sures of 30 to 100 pounds are more easily extracted than fresh livers. This 

 treatment appears to inactivate the enzymes of the livers and is recommended 

 where the livers are to be shipped to distant points for the final extraction of 

 vitamin A oil. 



Alkali-Digestion Method 



Livers of low oil concentration and high vitamin A potencies, including halibut, 

 rockfish, tuna, lingcod, etc., are most easily extracted with a low concentration 

 of sodium hydroxide (1 to 2 per cent by weight) or 2 to 5 per cent sodium car- 

 bonate (Young and Robinson, 1938). The livers are first ground in a meat chopper 

 or disintegrator to hasten the reaction. The temperature is held at 180-190° F 

 (82-88° C) until the solids of the liver are in the liquid stage, entirely releasing 

 the oil. The entire mass is agitated to increase the efficiency of the chemical 

 reaction and release the oil. The liquor is then passed through a 3-phase or 

 sludger-type centrifugal, which separates the oil in the form of an emulsion. The 

 pH of the emulsion is then adjusted to a suitable point so as to recover the oil as 

 completely as possible. Breaking the emulsion makes possible the delivery of a 

 marketable oil after it is passed through a properly adjusted purifying-type centri- 

 fuge. In cases where the purified oil contains suspended soaps or excess free 

 fatty acids, further refining is necessary. 



