in comparison with an untreated sample. An 

 increased absorption in the red end of the spec- 

 tram is noted due to the pigment, with normal 

 or less than normal reflection in the blue-green 

 region (400-500 millimicrons). Similarly the 

 slightly greater absorption in the red noted for 

 green tuna meat may be the source of the green 

 effect. 



Similar reflectance studies were made on 

 raw tuna whose color behavior on cooking was 

 known (fig. 4). It will be noted that, for the 

 few samples tested thus far, there is some 

 correlation between known greenness and the 

 reflectance of the raw flesh. A tendency toward 

 normal color is shown by a higher proportionate 

 reflectance in the red end of the spectrum 

 (light "pinkness") in uncooked sannples. The 

 relationship is rather tenuous, therefore fur- 

 ther experiments are needed to establish its 

 existence with certainty. 



LABORATORY COOKING METHOD 



In order to simplify the magnitude of the 

 cannery procedures necessary to produce 

 greening, laboratory cooking was attempted. 

 It was found that the color of 1-inch cubes of 

 meat cooked in a pressure cooker at 102 C. 

 indicated whether or not the fish from which 

 they were taken had any tendency to turn green 



under connmercial methods. A 10-minute cook- 

 ing time was sufficient to show this tendency; 

 longer periods gave an increased darkening 

 (browning?) of the meat. Spectrophotometric 

 reflectance curves, which summarize the color 

 difference produced by laboratory and commer- 

 cial methods of cooking can be seen in figure 5. 

 The green produced by the laboratory method 

 was not as intense as that produced by commer- 

 cial methods, probably because of concomitant 

 browning. It was also noted that normal cooked 

 flesh was less desirable in color than that pro- 

 duced commercially for the same reason. It 

 was necessary therefore, in making comparisons 

 between green and normal flesh, to be certain 

 that the cooking methods corresponded. 



THE NATURE OF THE PIGMENT 

 IN TUNA FLESH 



From what has been noted thus far, it is 

 evident that the understanding of the processes 

 that cause greening in tuna flesh must await an 

 understanding of the nature of the pigment in- 

 volved. It has been pointed out that the exist- 

 ence of the Soret absorption peak (410 millinni- 

 crons) in the reflectance curves is indicative 

 of the presence of a heme protein, however, 

 this still leaves the question of the exact nature 

 of the heme compound unsettled. It would be 

 expected that myoglobin, the hemoglobin found 



iij 80 

 O 



o 



UJ 60 



LlI 



ir 



40 



o 

 cr 



LJ 



Q. 20 







*33 



* 7 



— NORMAL 

 -- GREEN 



* 4 LIGHT GREEN 



* 6 VERY PINK 



400 440 480 520 560 600 640 680 

 WAVE LENGTH (MjJ) 



Figure 4. --Reflectance of raw tuna meat of known color behavior on cooking. 



4 



