88 U. S. BUREAU OF FISHERIES 



chinook, sockeye, and silver salmon, if prepared properly, will compare 

 favorably with U. S. P. requirements for medicinal cod-liver oil. 



Studies with regard to methods for manufacturing the fish oils 

 indicate that the common practice of cooking is not necessarily destruc- 

 tive to the vitamins extracted by the fats. Rather the vitamin 

 potency of the oils seems to depend upon the freshness of the raw mate- 

 rial, the extent to which the visceral parts are utilized in making the 

 oil, and the efficient mechanical extraction of the press liquors. 



As a corollary to these studies, our technologists gave assistance to 

 the industry in the development of edible salmon oils for use in canning 

 and conducted tests on the effect of adding high-grade salmon oil to 

 salmon during the canning process. Preliminary results indicate that 

 the addition of this oil is effective in improving quahty. 



Studies with respect to effect of manufacture on salmon meals were 

 started, but sufficient data are not available for making a preliminary 

 report. 



EFFFCT OF MANUFACTURE ON THE QUALITY OF NONOILY FISH 



MEALS 



Studies concerned with the effect of manufacture on the composi- 

 tion and nutritive properties of nonoily fish meals, which have been 

 in progress several years, were completed in 1933 and during the past 

 year the data have been assembled for use in reports. These studies 

 have shown: 



(1) Fish meal proteins, as shown by tests for feeding efficiency, 

 biological value, digestibility, and destruction of essential amino 

 acids, are not affected as much by conditions of drying as is vitamin 

 G. 



(2) Vitamin G is water soluble and is removed with the water 

 soluble protein by the wet process. 



(3) The water soluble proteins removed by the wet process are not 

 of as high quality as the residual flesh proteins. 



(4) The head portion of the waste is the richest source of vitamin 

 G, while the backbone and flesh portion has the highest quality 

 protein. 



(5) Flame drying is definitely destructive to vitamin G and de- 

 creases the value of the protein. 



From these data it is possible to draw certain practical conclusions, 

 some of which are: 



(1) Dry process meals have greater general nutritional value than 

 wet process meals, owing to the advantage given by vitamin G, in 

 the former, overbalancing the slightly higher quality proteins of the 

 latter. 



(2) Steam dried meals are superior to flame dried meals. 



(3) Steam drying under vacuum improves the value of a meal 

 slightly over steam drying at higher temperature. This is due more 

 to effect on vitamin G than on the protein. 



(4) Wet process oily fish meals cannot be expected to be important 

 sources of vitamin G. 



(5) From the standpoint of quality, there would be no particular 

 advantage in drying wet process meals under vacuum if normal steam 

 drying at atmospheric pressure can be accomplished. 



