12 CONTROL BULLETIN No. 113 



THE QUALITY INDEX OF MEAT AND FISH PRODUCTS 

 J. W. Kuzmeski and A. F. Spelman 



The chemical method used in evaluating the quality of the protein in the animal 

 and fish concentrates listed in this report was developed by H. J. Almquist, 

 E. L. R. Stokstad and E. R. Holbrook at the University of California. Experi- 

 ments conducted by there authors show that for animal and fish proteins the 

 value obtained by these chemical methods agrees closely with that obtained from 

 growth data of chick tests. The complete report of Dr. Almquist's work en- 

 titled "Supplementary Values of Animal Protein Concentrates in Chick Rations" 

 appears in the Journal of Nutrition, Volume 10, July-December, 1935 1 . 



It may not be generally understood that in routine laboratory practice, analy- 

 sis for total protein involves simply the determination of total nitrogen and the 

 application of the factor 6.25 to the percentage of nitrogen present (Nitrogen 

 X 6.25 = Protein). While the results may be approximately true as to protein 

 content, it is known that proteins are complex substances differing somewhat in 

 their nitrogen content and chemical make-up, depending upon the source from 

 which they are derived and subsequent treatment. In fish and animal products 

 used in feeding stuffs, a considerable portion of the nitrogen present may exist in 

 combinations which are not true protein, but in such form that the nutritional 

 value is either less than for true protein or at its worst negligible. The method of 

 Dr. Almquist is an attempt to fix the true value of what is ordinarily considered 

 as protein. 



The method consists of separating the total protein present into several com- 

 ponents which vary greatly in nutritive value. Since the terms used in designating 

 the various fractions may not be easily understood by the layman, the follow- 

 ing explanations are offered. 



1. Copper Precipitable Protein. This measures mainly the amount of intact 

 protein present, including the undigestible protein, the water soluble protein, 

 and to some extent the protein of decomposition products. Therefore, estima- 

 tion of undigestible and water soluble protein is necessary in order to determine 

 the content of the water insoluble, digestible, copper precipitable protein which 

 has the highest nutritive value. 



2. Phosphotungstic Acid Precipitable Protein. This fraction consists mainly 

 of peptones and amino acids present among the protein decomposition products 

 and indicates the degree of decomposition. 



3. Undigestible Protein. This measures mainly the protein derived from 

 hoof, horn, hair, and protein material which has been converted from the di- 

 gestible form by the use of high temperatures in cooking or drying. From a 

 nutritional viewpoint this pivtein has very little value. 



4. Hot- Water Soluble Protein. This is chiefly gelatin which is derived largely 

 from bone, cartilage, connective tissue, and skin. The nutritive value of this 

 fraction is comparatively low. 



5. Nitrogen in Non-Protein Combination. This consists mainly of ammonia, 

 amines, and urea, and includes all nitrogen not precipitated either by copper or 

 phosphotungstic acid. This fraction has relatively little nutritive value. 



By using the values obtained for the above fractions in a formula developed by 

 Dr. Almquist, it was possible to calculate the quality index of each of the listed 

 animal protein concentrates. It must be understood that the quality index does 



Mn addition to the published article of Dr. Almquist, acknowledgment is also made to H. R. 

 Bicknell, Chemist for the California State Department of Agriculture, for helpful correspondence. 



