508 MARINE PRODUCTS OF COMMERCE 



oxidation, which in turn causes an increase in the fatty acid and peroxide values 

 and a resulting loss of vitamin A potency. All containers for use in shipping oil 

 must be air-tight and filled as full as possible. The storage temperatures of the 

 oil are held near 35 to 40° F (2 to 5° C) since changes in the oil are retarded at 

 this range. Some refiners displace the air above the oil in containers with inert 

 gases, such as nitrogen and carbon dioxide. 



Extraction of Livers by Solvents 



The early attempts of the processors to make use of solvents to remove the oil 

 from high-potency livers were not highly successful. The solvents used removed 

 not only the oil and vitamin A, but also some coloring matter which was difficult 

 to eliminate. Such solvents as ether often contained peroxides as impurities, which 

 hastened the oxidation of the oil during the extraction period. The elevated tem- 

 peratures for the prolonged periods required for complete removal of the solvent 

 were another factor contributing to oxidation and loss of vitamin. Even refining 

 by means of alkali treatment did not completely overcome the discoloration, 

 though it did remove the fatty acids. 



Later the processors took advantage of information gained by the extractors of 

 some vegetable oils and found solvents which are not so objectionable as those 

 used earlier. At present, use of the solvent process for the extraction of oil is gaining 

 popularity as a result of the development of new, more efficient solvents and the 

 availability of more highly purified ones than those previously used. These elimi- 

 nate many of the difficulties previously mentioned in solvent extraction processes. 



Processing by Alkali Digestion 



The most generally used method by far for the recovery of vitamin A is the 

 treatment by the alkali digestion process or some of its many modifications. The 

 nature of this process itself serves to inactivate the enzymes and reduce the fatty 

 acids of the refined oil. The amount of alkali used is carefully adjusted and chemi- 

 cally controlled so that it is never more than slightly in excess. This results in 

 holding the formation of emulsions to a minimum and prevents the excessive loss 

 of adsorbed vitamin A in the water phase. 



Research is under way for the investigation of oxidation of vitamin A oils pro- 

 duced by this method and held for long storage periods. The loss of vitamin A 

 potency in these oils is one of considerable economic importance to the industry. 

 The condition of the livers has been found to be of major importance as a con- 

 tributing factor in the keeping quality of the final product. 



Processing Equipment 



Butler (1948) gives the following suggestions for the establishment of a liver- 

 oil extraction plant for the processing of high vitamin A livers: 



"Many types of equipment can be used for the preparation of vitamin oils. In the 

 selection of the equipment for a particular plant some of the items to be considered 

 are: (1) kind and volume of material, (2) process contemplated, (3) availability and 

 relative cost of power and heat from the various sources such as electricity, steam, water 

 power, internal combustion engines, etc., (4) amount of mechanization and automatic 

 control, ( 5 ) cost and availability of labor. 



