506 MARINE PRODUCTS OF COMMERCE 



method for producing the highest potency oil possible from the livers. If he is not 

 ready to proceed with immediate extraction of the livers, he can place them in a 

 freezer and store them for several months without serious loss of vitamin A. 

 Frozen livers stored at a temperature as low as — 20° F (— 29° C) undergo only 

 shght change since the tight can protects them from the air and dehydration. 



In trade practice the term "fresh" is applied to all raw material which has not 

 been frozen or preserved by other means. If the livers have not been preserved, 

 they have undergone some decomposition; this tends to cause the formation of 

 free fatty acids, which will be carried into the finished oil. It is also possible for 

 the livers to develop odors of decomposition which will eventually appear in the 

 finished product, and thus lessen its value. 



Viscera 



Some Canadian producers of vitamin A oils use the viscera as well as the livers. 

 This has been attempted from time to time in the United States by pharmaceutical 

 firms, etc. One of the chief difficulties to overcome has been the high moisture 

 content of the viscera. Since the use of the viscera is not practiced generally in 

 the United States, probably due to the low recovery of vitamin A, it is not of com- 

 mercial importance. 



Preservation of Livers 



Freezing and Storing. The most generally used method of preserving livers is 

 by freezing. When the livers are removed from the fish on board the vessels, they 

 are packed in 5-gallon square cans, with a telescope-type round cover. The cans 

 are filled as nearly full as possible so that the enclosed air is reduced to a minimimi. 

 This is to prevent oxidation of the oil by entrapped oxygen of the air. The com- 

 pletely filled cans are closed and packed in cracked ice in the hold of the vessel. 

 When it reaches port, the cans are removed immediately to the freezer if the oil 

 is not to be extracted at once. If the processor purchases more livers than he can 

 handle for a few days, he may take them out of the 5-gallon cans and place them 

 in a large 50-gallon drum fitted with a clamp top and freeze them. The usual 

 freezer temperature is — 20° F (— 29°C) or lower. At this temperature the 

 enzymatic and bacterial action is either very slow or completely arrested. The livers 

 may be held for several months in frozen storage without any considerable in- 

 crease in the fatty acid content. 



Since vitamin A is probably contained in the protein of the liver as well as oil, 

 the rupture of the cellular structure has little, if any, effect upon the final recovery. 

 Freezing may release a large portion of the oil which will float to the top of the 

 container, when the livers are defrosted. This increases the difficulty of obtaining 

 an accurate sample for determining the vitamin A potency. 



In planning for the processing of frozen livers it is necessary to defrost a suf- 

 ficient supply to keep the plant in operation throughout the day. If for any reason 

 the process is slowed down, it may be found that too great a quantity of livers 

 has been defrosted, and thus a problem of deterioration is created. 



Preservation by Salting. Considerable quantities of livers are landed in ports 

 where there are no facilities for freezing. In many of these there is not even 

 sufficient ice for adequately storing the livers on board the vessels until they are 

 landed. In this case salt is usually used as a preservative. This method is common 



