l-t-'4 



-10 - 



\ 



-19 

 -20- 



-1/1- 



\ 



1.0 I.I 1.2 1.3 1.4 



630/660 PEAK RATIO 

 Figure 12. --Relation of metmyoglobin content 

 of raw tuna flesh (as judged by magnitude of 

 spectral reflectance at the 630/660 peak ratio) 

 to the color rating of the same meat on pre- 

 cooking as subjectively judged. 



o 1.7 



o 

 t 1-5 



630/660 PEAK RATIO 



Figure 1 3. --Relation of metmyoglobin content 

 of raw fishfleshto color as objectively judged 

 (540/640 ratio). Measurements made from 

 absorption in spectral reflectance. 



metmyoglobin, was used as an indication of the 

 amount of this pigment in the raw meat and was 

 measured by means of the ratio of 630/660 

 nnillimicron absorption. Offcolor of the same 

 meat on precooking was judged subjectively by 

 Mr. Jermann of Hawaiian Tuna Packers on a 



plus one (excellent); zero (normal); minus value 

 (for increasing degrees of greenness and off- 

 color) scale. The results are shown in figure 

 12. There seems to be a definite relation 

 between these factors when judged in this nnanner . 



Objective evaluation of greenness in pre- 

 cooked meat was made through the use of the 

 absorption ratio at 540/640 millimicrons de- 

 scribed earlier in this report. The comparison 

 of this color rating with the metmyoglobin con- 

 tent is shown in figure 13. Again we note the 

 indication of an interrelation, complicated by 

 the orange color abnormality that is sometimes 

 noted. It is rather surprising that this also 

 seems to be related to a high metmyoglobin 

 content. The large number of coexisting flesh 

 pignnent forms and color s(pink, orange, green, 

 and brown) gives a complicated system in which 

 correlating factors are readily obscured. None- 

 theless, the evidence seems to point rather 

 definitely to metmyoglobin as a factor in the dis- 

 coloration of tuna flesh. 



PEROXIDES IN FISH FATS 



The suspicion of oxidation as one factor 

 related to greening leads one to speculate on the 

 role of fat peroxides in this phenomenon. The 

 coupled oxidation of hemoglobin and unsaturated 

 fats in mammalian meat tissue has been the sub- 

 ject of much research, summarized by Watts 

 (1954). The oxidation of unsaturated fats to 

 peroxides is accelerated by heme compounds 

 and is accompanied by the oxidation of the h enae. 

 The resulting fat peroxide may, in turn, play a 

 role in furthering the deterioration of hemepig- 

 nnents. It is known that hydrogen peroxide forms 

 unstable addition compounds with hemoglobin , 

 which subsequently deconaposed with destruc- 

 tion of the heme moiety of the molecule (Keilin 

 and Hartree 1950). We have observed a green- 

 ing of tuna meat on treatment with dilute solu- 

 tions of hydrogen peroxide. 



To test the possibility of a correlation 

 between peroxide formation and oxidation of the 

 heme pignnent, we have determined the fat con- 

 tent flesh by a modification of the cold extraction 

 method of Sperry (1955), carried out in de- 

 aerated solutions under a blanket of nitrogen. 

 The peroxide content was determined by titra- 

 tion of the iodine released fronn an iodide solu- 

 tion by the peroxide present in the extracted fat 

 with a standard thiosulfate solution. Appropriate 

 blank determinations were made. The results 

 are given in table 3. 



For the sannples run, there is an indica- 

 tion of a high peroxide content in green and 



