From Tables 9 and 10 it is apparent that the 

 essential amino acids of hydrolysates prepared 

 under these process conditions compare favor- 

 ably with the corresponding concentrations in 

 the starting material. In the isopropyl alcohol 

 extraction process low quality soluble proteins 

 and nonprotein nitrogen are washed out in the 

 miscella. This results in higher concentrations 

 (as percent of total crude "protein") of essential 

 amino acids in the FPC than are contained in 

 the raw fish. 



Protein efficiency ratios (PER)— PER were 

 determined by rat feeding trials with the prod- 

 ucts prepared from hake and alewife. The 

 products prepared from whole red hake were 

 inferior to casein as a sole source of protein in 

 the diets but were statistically equivalent to 

 casein as a supplement to wheat flour. PER for 

 hake products as a sole source of protein are 

 listed in Table 11. The low PER for II-A-40, 

 the 20-gal Alcalese digest, corresponded with a 

 low yield and tryptophan concentration. An ex- 

 cessively high pH was reached during hydrol- 

 ysis due to an electrode malfunction. The rea- 

 son for the low PER of II-PC-40 is not clear, 



Table 11. — Nutritive quality of hydrolysates produced 

 from red hake by enzymatic hydrolysis. 



but centrifugation was more difficult than for 

 the smaller pancreatin batches and additional 

 heating and acidification were required. Despite 

 the low PER of two of the 20-gal batches as a 

 sole source of protein, they were all very ef- 

 fective as a supplement to wheat flour as is 

 shown in Table 12. 



The results of feeding tests with the alewife 

 (river herring) products are listed in Table 13. 

 From the fatty fish alewife, we finally succeeded 

 in obtaining a totally water-soluble FPC product 

 which was statistically equivalent to casein as a 

 sole source of protein. It was prepared by di- 

 gestion of the whole fish with the alkaline pro- 

 tease, Alcalase. Partially soluble products pre- 

 pared from raw whole alewife and from alewife 

 press cake were also equivalent to casein as a 

 sole source of protein. 



Several methods were tried for correlation of 

 the PER of various fish protein hydrolysates 

 with the corresponding amino acid analyses. In 

 Figure 9, PER are plotted versus chemical scores 

 based on the amino acid analysis for whole egg 

 as reported by Block and Boiling (1950). The 

 results of earlier feeding trials with hake prod- 

 ucts prepared with a number of different en- 

 zymes and processing conditions are included. 

 Only one of these products was equivalent to 

 casein as a sole source of protein. It was a par- 

 tially soluble Bromelin digest and included the 

 insoluble sludge which, in this particular case, 

 had been extracted once with isopropyl alcohol. 

 Another product, a soluble pancreatic digest, 

 was supplemented with tryptophan and histidine 

 in a feeding experiment. Neither of the amino 

 acids added alone changed the PER significantly, 

 but when both were added to the same diet there 

 was a marked improvement in PER. 



Table 12. — Supplemental value of hake hydrolysates when added to wheat flour (total protein 



10% of diet). 



Sample 

 No. 



Enzyme 



Sample protein - 2% of diet 

 wheat flour protein - 8% 



Sample protein - 4% of diet 

 wheat flour protein - 6% 



PER 



Ratio of PER to 

 wheat protein PER 



PER 



Ratio of PER to 

 wheat protein PER 



' PER = Protein efficiency ratio. 

 " Standard error of the mean. 

 "• Partially soluble product. 



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