2.0 



1.9 - 



«> 16 



V. 



O 



■a- 



u 



07 08 0.9 10 II 1,2 

 ABSORBANCY AT SORET PEAK 



Figure 2. --Variation of the 540/640 millimicron 

 peak ratio with absorbancy at Sore t peak 

 (410-415 millimicrons), an index of pignnent 

 content. 



figure indicative of higher 540/640 peak ratio 

 as would be expected, and lower pignnent con- 

 tent. It is noteworthy that both the "albacore 

 white" color resulting from low pigment content 

 and the fleshy pink color associated with a high 

 540/640 peak ratio are accepted as nornnal by 

 observers, thus emphasizing the complexity of 

 the systems encompassed by the term "normal. " 

 Another relationship which can be noted here, 

 namely the association of offcolor with a high 

 pigment content, is completely contrary to the 

 supposition expressed above; that is, that the 

 appearance of greenness is due to a lack of pig- 

 ment. It should also be noted in passing that 

 the overlapping position of some of the points 

 is due to the uncertainty inherent in the subjec- 

 tive evaluation of precooked flesh. 



NATURE OF THE PIGMENTS IN TUNA FLESH 



It is obvious that in an investigation of pig- 

 ment changes it is necessary fir St to under stand 

 the nature of the pigment. It is to be expected, 

 in a muscle system such as tuna flesh, that 

 muscle hemoglobin (myoglobin^./) would be the 

 major pigment present and contribute the larg- 

 est part of the flesh color. We had assumed 

 this in the investigations herein described, but 

 certain experiments have cast some doubt on 

 the validity of the assumption. It was found by 

 Bowen (1949) and others that the absorption 



— Myoglobin is similar to hemoglobin 

 except for its lower molecular weight. 



peaks for mammalian myoglobin were displaced 

 to longer wave lengths in the case of certain 

 derivatives of the pigment. No such shift was 

 observed for fish flesh. 



The curves in either transmission or re- 

 flection for the systenns studied were identical 

 with those that we have nneasured for hennoglobin 

 and its derivatives. For verification, the solu- 

 bility of the extracted pigment in buffered phos- 

 phate solutions was checked according to the 

 procedure of Morgan (1936), with the incorpora- 

 tion of the modifications of Ginger, Watson, and 

 Schweigert (1954). The absorption curves for 

 the separated pigments are given in figure 3. 

 Assuming that these procedures would give 

 separation of myoglobin from the hemoglobin of 

 tuna flesh through differences in solubility, it 

 was found by measurennent of absorption in trans- 

 mission and reflection that the tuna pigment was 

 about 95 percent hemoglobin. Myoglobin seemed 

 to comprise only a minor fraction of the pigment 

 system. In figure 3 note the residual myoglobin 

 (curve b) in relation to the total pigment content 

 of the extract (curve a). It is felt that these 

 experiments were not exhaustive enough to be 

 conclusive. As far as color changes are con- 

 cerned, the division of the pigment between 

 myoglobin and hemoglobin is not too pertinent 

 since these changes involve the porphyrin 

 moiety of the pigment molecule which is identi- 

 cal for the two types. For convenience, we 

 shall continue to ascribe the color to myoglobin 



1.0 r-i^ 



IT 



o 



in 

 m 

 < 



Ol-^^ 



400 450 500 550 600 

 WAVE LENGTH, MJU 



650 



700 



Figure 3. --Separation of aqueous extract of raw 

 tuna (No. 6) into hemoglobin and nnyoglobin by 

 phosphate fractionation. (a) Transmission 

 curve for original extract, (b) Transmission 

 curve for residual solution after hemoglobin 

 precipitation with phosphate, (c) Reflectance 

 curve of phosphate precipitated material. 



