It is interesting to examine the reflectance 

 curves with the possibility of qualitatively and, 

 in a relative way, quantitatively making an esti- 

 mate of the pigments present. It would be 

 expected that the reflectance curves would re- 

 semble the well-known absorption carves for 

 the heme pigments that might be involved, and 

 examination reveals this to be the case. 



Raw Meat (fig. 4). Two conditions will be 

 noted, first, a normal type of curve with a vari- 

 ation in over-all position (brightness) due to 

 variation in the amount of pigment present (com- 

 pare curves for samples No. 6 and No. 33, fig. 

 4), and second, curves of a different shape (com- 

 pare curves No. 4 and No. 7 with curve No. 33, 

 fig. 4). Disregarding the Soret peak (about 410 

 millimicrons), other "peaks" (actually depres- 

 sions in the curve) can be detected at 540 and 

 580 millimicrons, indicative of oxyhemoglobin 

 or oxymyoglobin, and at 500 and 630 millimi- 

 crons, indicative of methemo- or metmyoglobin. 

 K comparison is nnade with normal flesh (No, 33), 

 it will be noted that the concentration of the oxy- 

 compound is about the same in green and normal 

 (No. 4 and No. 7, and No. 33). A higher concen- 

 tration of the methemoglobin or metmyoglobin is 

 indicated by reducedpercent reflectance for the 

 green tuna, however. The over-all condition 

 seems to be, then, that similar pigments are 

 present in green and normal raw flesh, with a 

 higher concentration of oxidized methemoglobin 

 or metnnyoglobin in the green. 



Various experiments were tried in an 

 attennpt to artificially produce color changes in 

 tuna flesh. It was found that soaking raw normal 

 flesh in 0. 3 percent hydrogen peroxide solution 

 imparted greenness after cooking. Also, soaking 

 raw incipient greenflesh in reducing agents such 

 as ascorbic acid improved the color of the green 

 meat after cooking. These effects are what would 

 be expected fronn the normal reactions of hemo- 

 or myoglobin pigments with hydrogen peroxide, 

 or with reducing agents. 



Cooked Meat (fig. 2). On cooking, the meat 

 exhibits similar variations in the reflectance 

 curves as noted for raw flesh (fig. 4). The 

 curves reveal maximum absorption at about 540 

 and 575 millimicrons, characteristic of denatured 

 globin hemichrome. Absorption maxima are 

 also noted at about 650 nnillimicrons and for 

 green fish a significant flattening in the region 

 of 440 to 490 nnillimicrons, probably also due 

 to absorption. Neither of these latter regions 

 of absorption can readily be connected with com- 

 nnon pigments of the hemo-myoglobin type, or 

 their derivatives. 



By way of a further check on these observa- 

 tions, samples of the same cooked meat were 

 reduced with dithionite and the reflectance curves 

 were examined (fig. 6). Save for the abnormally 

 pink sample (No. 6), all samples were found to 

 have about the same reflectance. A pink color 

 was induced in the green meat on reduction. A 



100 



r-t^ 



400 



440 



480 520 560 600 



WAVE LENGTH ( M|l ) 



640 



680 



Figure 6. --Reflectance of reduced cooked tuna of various colors in the unreduced state. 



6 



