Table 2. --Acid-hematin absorption peaks 



550 600 650 550 600 650 



WAVE LENGTH , M/J 



Figure 1 1. --Reflectance curves of acid-acetone 

 (a, b, c) and acid-methanol (d, e) extracted 

 precooked tuna of decreasing greenness (a, b 

 to c; and e to d). The decrease in absorption 

 with the decrease in greenness in the 610-620 

 millimicron range is evident. 



previously been deduced more or less indirectly. 

 A similar pigment, absorbing between 610 and 

 620 millimicrons, has been reported in both 

 transmission measurements on green-colored 

 extracts and spectral reflectance curves obtained 

 from discolored beef that had been exposed to 

 gamma radiationfrom a cobalt-60 source (Ginger, 

 Lewis, and Schweigert, 1955). The pigment noted 

 here may be sinnilar, although present in lower 

 concentration and in an insoluble coagulated form. 

 The exact nature of the pigment is still under 

 investigation. 



RELATION BETWEEN PIGMENTS OF RAW 

 AND PRECOOKED TUNA FLESH 



The examination of many spectral reflec- 

 tance curves for the flesh of raw tuna reveals the 

 tendency for flesh with a high content of metmyo- 

 globin, characterized by a prominent 630- 

 millinnicron absorption peak, to give an offcolor 

 on precooking. Thus, referring to figure 4, one 

 would usually find that raw meat which gave a 

 reflectance curve such as (b) would turn green or 

 gray-green on precooking. The picture is com- 

 plicated by the presence of oxymyoglobin, which 

 seems to modify the effect of metmyologbin and, 

 when present in high concentration, produces 

 pink nneat that browns rapidly on exposure to air. 

 Frequently a high concentration of both oxymyo- 

 globin and metmyoglobin is found. The oxymyo- 

 globin predominates in effect, and the possible 

 combinations seem to result in a gamut of gray 

 to brown to orange pigmentation depending on the 

 relative amounts of each parent pigment. 



where the absorption peak has disappeared. A 

 similar effect is noted in the acid-methanol 

 treatment (curve d, normal; curve 3, green 

 nneat). It is felt that this peak is direct evidence 

 for the green pigment, the existence of which had 



An evaluation of the relation of both sub- 

 jectively and objectively judged color to metmyo- 

 globin content is shown in figures 12 and 13. The 

 height of the absorption peak in the red region at 

 630 millimicrons, which is characteristic of 



