lack of oxygen, in the muscle of the fish brought 

 on by exhaustion might lead to a high metmyo- 

 globin content with consequent increased inci- 

 dence of greening. Such a condition is probable 

 for certain fish caught by the longline method 

 of fishing. 



An opportunity to test the theory was 

 afforded through the utilization of the facilities 

 of the Coconut Island Marine Laboratory of the 

 University of Hawaii. A fishing boat was avail- 

 able with a "live-well" in which it was possible 

 to maintain small tuna alive. In addition, 

 small yellowfin tuna abound in local waters in 

 certain seasons. With the cooperation of the 

 staff of the Hawaii Marine Laboratory, it was 

 possible to catch tuna with lures and to kill 

 certain of these within a few minutes of capture 

 while maintaining others in a wounded and dying 

 condition for many hours in the live-well. The 

 latter were finally killed and the flesh of both 

 types was analyzed for metmyoglobin by the re- 

 flectance technique. Two sets of such paired 

 samples were obtained. Differences in met- 

 myoglobin content were very slight and seemed 

 to be randomly distributed between the fish 

 killed under the two conditions. 



DISCUSSION 



renders the heme moiety nnore susceptible to 

 further oxidation, which takes place on precook- 

 ing, and results in an opening of the porphyrin 

 ring. This last process may result in the pro- 

 duction of pigments similar to verdohemo- 

 chromes, which impart a green color to the 

 meat. Concomitant browning occurs due to the 

 formation of denatured globin hennichromes. 



Although this picture is hypothetical, 

 there is some evidence for the steps indicated, 

 and it is offered as a basis for further work. 



SUMMARY 



Continued work on the green or offcolor 

 condition that appears in the flesh of certain 

 specimens of tuna on precooking has indicated 

 the following: 



1. The greenness is an actual color condition, 

 rather than a lack of pigment or offcolor. 



a. ICI (International Commission on lUunni- 

 nation) color evaluation of the light 

 reflected from green meat shows it to be 

 in the yellow-green region, with some - 

 what more green color than is present 

 in normal meat. 



Consideration in toto of the experimen- 

 tal work performed in t h e period covered by 

 this report reveals that it was guided by the 

 assumption, based on evidence gathered in 

 earlier experiments, that there i s an actual 

 green pigment that produces the undesirable 

 color in certain samples of precooked tuna. As 

 a working hypothesis, it has been assumed that 

 the green color is due to the pignnents that result 

 from the opening of the porphyrin ring of certain 

 of the heme proteins of tuna flesh. This process, 

 which takes place as a result of oxidation, is 

 familiar to food scientsts in the meat industry. 



A hypothetical picture of the processes 

 occurring in the greening of precooked meat 

 follows. Certain samples of raw tuna flesh con- 

 tain a high concentration of metmyoglobin in 

 proportion to the oxymyoglobin content. There 

 is evidence that such tuna are prone to green- 

 ness on precooking. The high concentration of 

 metmyoglobin is a result of the decomposition 

 of oxymyoglobin which releases oxygen in an 

 active form capable of oxidizing the ferrous iron 

 of myoglobin, and also capable of producing a 

 denaturation of the protein moiety of the heme 

 protein molecule. This oxidation takes place 

 largely during storage after the death of the 

 fish, and may be catalyzed by the presence of 

 certain fats ingested as a result of peculiarities 

 of the fish diet. The denaturation of the pigment 



b. Study of spectral reflection shows gen- 

 erally a greater relative absorption of 

 light in the red region of the spectrum 

 for green meat--hence the green color-- 

 and indicates a higher concentration of a 

 conripound or mixture of compounds ab- 

 sorbing in this region (thegreen pigments). 



c. Evidence is offered for a green pigment 

 in precooked meat that has been exposed 

 to hemin cleavage by chemical means. 



Spectral reflectance studies reveal oxymyo- 

 globin and metmyoglobin as the chief pig - 

 ments of raw tuna flesh. Mixtures are usually 

 present with a high concentration of oxymyo- 

 globin in the freshest meat, and increasing 

 concentrations of metmyoglobin in older 

 stored meat. Metmyoglobin content increases 

 even on freezer storage. 



The reactions of the pigments in situ in the 

 raw tuna flesh were studied by reflectance 

 methods and revealed the following: 



a. Interconversion from oxy- to met- to 

 myoglobin, and reverse were readily 

 achieved by chennical means. 



b. Metmyoglobin was found to be very soluble 

 in aqueous media while oxymyoglobin was 



11 



