MILLER and SPINKLLI: EFFECT OF PROTEASE INHIBITORS ON PROTEOLYSIS 



Table 4.— Effect of dibasic phosphate peroxide on 

 proteolysis in ground parasitized Pacific whiting- 



were effective in inactivating the parasitic 

 enzyme in parasitized Pacific whiting. We then 

 determined whether 1) the inactivation would be 

 maintained during a freeze-thaw cycle after 1 

 mo of storage at — 20°C, 2) inactivation was suf- 

 ficient to maintain a desirable texture, and 3) the 

 treatment with oxidizing agents would adverse- 

 ly affect the amino acids, thereby decreasing the 

 nutritional quality of the protein. 



Effect of Frozen Storage 



The prolonged effect of frozen storage on in- 

 hibition was determined on samples of ground 

 parasitized Pacific whiting treated with various 

 inhibitors. Aliquots of these samples were tested 

 at the time of preparation for percent inhibition 

 and the presence of oxidant residues. All samples 

 were stored at — 20°C for 1 mo at which time these 

 tests were repeated, and as the results show in 

 Table 5 there was no decrease in the inhibition of 

 proteolysis. The ground fish treated with 0.5% 

 H2O2 had no detectable residues even imme- 

 diately after treatment, but maintained the in- 

 activity of the enzyme. The residual bromate was 

 dependent on concentration. The samples con- 

 taining 0.025% and 0.05% KBr0 3 still had slight 

 amounts of bromate. Bushuk and Hlynka (1960) 

 reported that 80 ppm of bromate in bread dough 



disappeared completely after baking for 20 min. 

 We baked portions of ground fish, treated with 

 0.05% KBr0 3 , for 20 min at 162°C. There were no 

 detectable residues indicating there would not 

 be significant residues in normally cooked fish. 



Effect of Inhibition on Texture 



Results of the organoleptic evaluation for tex- 

 ture are shown in Table 6. These results demon- 

 strate that there is a correlation between the per- 

 centage of inhibition and the maintenance of 

 firm texture. Samples which had the highest 

 inhibition were judged to have texture compar- 

 able with nonparasitized fish. 



Oxidative Effect on Amino Acids 



Some amino acids are susceptible to oxidation, 

 particularly methionine which is readily 

 oxidized to methionine sulfoxide and, under 

 severe conditions, to methionine sulfone. We 

 were using relatively mild conditions compared 

 with other investigators, but we lacked informa- 

 tion on the effect of potassium bromate or the 

 combination of potassium bromate and hydrogen 

 peroxide. We therefore compared the amino acid 

 profiles of acid hydrolysates of nonparasitized 

 Pacific whiting, parasitized with no treatment, 

 and two samples of parasitized ground fish, one 

 of which was treated with 0.5% Na 2 HP0 4 H 2 02 

 + 0.025% KBr0 3 , the other with 0.5% K 2 HP0 4 - 

 H2O2 + 0.025% KBr0 3 . We compared the profiles 

 for differences that might suggest significant de- 

 struction of any of the amino acids. Acid hydrol- 

 ysis converts methionine sulfoxide to methionine 

 so a difference would only show if methionine 

 were converted to methionine sulfone. No signif- 

 icant differences were found in any of the amino 

 acids (Table 7). 



Table 5.— Storage study of oxidants in ground parasitized 

 Pacific whiting. 



'Storage at -20°C 



2 + = presence of residue oxidant. 



3 N.D. = not detectable. 



Table 6.— Texture evaluation of treated parasitized Pacific 



whiting. 



Sample and treatment 



Texture 

 evaluation 



Nonparasitized Pacific whiting 

 Parasitized Pacific whiting— no treatment 

 Parasitized Pacific whiting treated 



with 0.5% H 2 2 

 Parasitized Pacific whiting treated 



with 05% KBr0 3 

 Parasitized Pacific whiting treated 



with 5% Na 2 HP0 4 -H 2 2 + 025% KBr0 3 

 Parasitized Pacific whiting treated 



with 0.5% K 2 HP0 4 H 2 2 + 0.025% KBr0 3 

 Parasitized Pacific whiting treated with 



5% K 2 HP0 4 -H 2 2 



% 

 inhibition 



'Categories: 1 = firm, 2 = soft. 3 = mushy 



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