of distribution. A low tryptophan concentra- 

 tion in the soluble fraction was accompanied by 

 an abnormally high concentration in the insol- 

 uble solids remaining-. Increasing the yield of 

 soluble product resulted in a higher concen- 

 tration of tryptophan in the product. This is 



Table 6. — Means and standard deviations of chemical 

 scores for soluble hake products grouped according to 

 type of enzyme and pH of digestion. 



Enzymes 



„ Number Chemical score, 

 pH c average ± 



■■^S" samples f^^'^ 

 '^ deviation 



Pepsin 2-2.5 



Autolysis 4.5 



Autolysis 6.6-7 



Papain . . 

 Bromelin 

 Ficin . . . 



5.7-6.8 



Bacterial Protease Novo/ -__ 

 Monzyme J 



Rhozyme P-11 

 Rhozyme 41 . . 



Pancreatin . . . 

 Trypsin 



Alcalase 



ABP 



P-58 



E-56 



8-8.4 

 7-9 



\. 8.5-10 



4 

 3 

 4 



10 



5 



7 



15 



13 



25.5 ± 6.9 

 20.7 ±3.1 



41.3 ± 5.3 



42.7 ± 9.3 



54.0 ± 4.9 



45.0 ± 13.4 



60.0 ± 5.6 



64.2 ± 5.4 



' Based on rat requirements as determined by Rama Rao, 

 Metta, and Johnson (1959). 



1.0 



0.8 



;o.6 



;o.4 



;0.2- 



. . ^''' 



• •. 



t 







4 6 



pH HYDROLYSIS 



10 



12 



Figure 7. — Effect of pH of hydrolysis on the tryptophan 

 concentration in soluble FPC. 



illustrated in Figure 8. Tryptophan concentra- 

 tion climbs sharply with yield and is at a max- 

 imum at soluble solids yields of 13% and above. 

 Since yields from straight autolysis of raw red 

 hake averaged only 10%, it has not been possible 

 to obtain a totally soluble product with adequate 

 tryptophan without the addition of commercial 

 enzymes. 



Histidine concentration. — The concentration 

 of histidine in soluble products was highest for 

 pepsin hydrolyses at pH 2 and declined with in- 

 creasing pH of hydrolysis to a minimum recov- 

 ery in products prepared at pH 8. Fairly good 

 histidine concentrations were obtained in hy- 

 drolysates prepared at pH 8.5 and above. Low 

 concentrations of histidine under slightly alka- 

 line conditions are not due to a preferential dis- 

 tribution in the sludge, as is the case with tryp- 

 tophan. This is illustrated in Table 7 in which 

 amino acid recoveries in the soluble products 

 and in the solubles and sludges combined are 

 listed for four different processes. Digestion at 

 pH 8 with pancreatin resulted in a poor recovery 

 of histidine in both soluble and sludge fractions. 

 A 2-stage digestion, autolysis at pH 4 followed 

 by hydrolysis of the sludge at pH 8, gave a better 

 histidine recovery but tryptophan recovery was 



l.On 



-■ 0.8 



;o.6 



!0.4 



0.2 



I 



± 



8 10 12 14 16 18 



PERCENT YIELD OF SOLUBLE SOLIDS FROM FISH 



Figure 8. — Tryptophan concentration in soluble solids 

 versus percent yield of solubles from enzymatic hydrol- 

 ysis of red hake. 



17 



