400 



450 500 550 600 



WAVE LENGTH , M/J 



650 



700 



Figure 8. -- Reflectance curves showing solubil- 

 ity of metmyoglobin and insolubility of oxymyo- 

 globin in raw tuna flesh, (a) Raw tuna flesh. 

 (b) Residual flesh after aqueous extraction at 

 pH 6. 8. Note disappearance of 500 mp. and 

 630 n-i^i metnnyoglobin absorption peaks. 



content. This effect may be one of the complex 

 of factors related to greening, but it is probably 

 more closely related to a "washed out" condition 

 occasionally observed in tuna flesh. 



PIGMENTS IN COOKED TUNA FLESH 



400 



450 500 550 600 



WAVE LENGTH, M;U 



650 



700 



Figure 9. --Reflectance curves showing pigments 

 of cooked tuna flesh. Curves (a) and (b) de- 

 natured globin hemichrome of cooked tuna flesh. 

 Curve (c) denatured globin hemochrome of 

 reduced cooked tuna flesh. 



seems to lie in the greater absorption by the 

 former in the redregion (620 - 660 millimicrons) 

 for a given absorption in the yellow-green region 

 (520 - 580 millimicrons). Thus, infigure9, curve 

 (b) would be characteristic of flesh with a greener 

 hue than the flesh represented by curve (a). 



The cooking of tuna meat results in the 

 denaturation and coagulation of the proteins 

 present, with consequent lightening of the meat 

 color. Denaturation of the heme protein pig- 

 ments leads to the formation of the hemochrome 

 (ferrous form), and under oxidative conditions 

 the hemichrome (ferric form) of the denatured 

 globin. Characterizing absorption, aside from 

 the Soret region, occurs at 545 and 575 milli- 

 nnicrons (fig. 8, curves a and b) in agreement 

 with the values listed for the denatured globin 

 hemichrome of hemoglobin (Lemberg and Legge 

 1949, p. 228). It will be noted by examination 

 of figure 9 that absorption by this substance is 

 rather weak and the peaks are ill defined. A 

 more unique and more easily characterized 

 curve is obtained for the reduced, or ferrous, 

 denatured globin hemochrome, as has been dis- 

 cussed previously. The contrast is evident in 

 figure 9. The color of the reduced hemochrome 

 is pink and more desirable from the consumer's 

 viewpoint. Brown and Tappel (1957) recently 

 have identified this pink compound as being a 

 mixed, denatured, globin nicotinamide henno- 

 chrome. 



The difference between the spectral reflec- 

 tance curves of green and normal fish flesh 



GREEN PIGMENT IN PRECOOKED FLESH 



It proved to be impractical to extract and 

 identify the green component in precooked green 

 flesh, as has been pointed out previously. Another 

 approach would be to cleave the pyrrole ring 

 segment from the protein moiety of the pigment 

 molecule by alcohol--or acetone--hydrochloric 

 acid treatnnent, and then examine the extract by 

 spectral transmission, and the residue by spec- 

 tral reflection. Green pigmentation in meat has 

 been attributed to an oxidative attack on the 

 pyrrole ring of the heme pigments, with the 

 resultant production of choleglobin or verdohemo- 

 chrome (Watts 1954). Removal of the oxidized 

 or disrupted ring by the acid-alcohol or acetone 

 treatnnent, and spectral examination, would be 

 expected to reveal the nature of the parent pig- 

 ment. Verdohemochrome, and its postulated 

 precursor choleglobin, would produce biliverdin- 

 like compounds (Lemberg and Legge 1949, p. 

 458). 



The acid-methanol or acetone extracts gave 

 an absorption curve in transmission that showed 

 no characteristic absorption peaks and was very 

 similar to that obtained from the leachate of 

 cooked fish (fig. 10, curve b). Solvent extraction 



