AT SEA 



(HANDLING 

 CHILLING 

 FREEZING 

 HOLDING 

 THAWING) 



DENATURED 

 MYOGLOBIN 



OXYMYOGLOBIN 



METMYOGLOBIN 



// 



OXIDATION AS AFFECTED BY 

 PROOXIDANTS, STORAGE, pH, ETC. 



UNCHANGED 

 MYOGLOBIN 



/ 



CANNERY 



(PRECOOKING 

 CLEANING 

 CANNING) 



"GREEN" TUNA PRODUCTS 

 EXPOSURE OF CAN CONTENTS TO AIR 



\ 



DOES THE 'DENATURED' 

 MYOGLOBIN FORM HEM'D- 

 CHROMES AND HEMICHROMES? 



SPONTANEOUS REDUCTION 

 IN CANNED STORAGE 



Figure S.^Hypothetical diagram of the changes which tuna heme pigments may undergo in the course of 



catching and canning. 



at pH 5.8, the following first order oxidation 

 rates were found at different temperatures 

 (K X 103 hr-^. 



Oxidation Rates (K x 10^ hr"'). 



Temperature 



Yellowfin Mb Bigeye Hb 



22° 

 9° 



-2° 

 -10° 

 -20° 



(not frozen) 



(frozen) 



(frozen) 



120 



25 



5 



40 



75 



50 (10= 

 5 

 175 



C) 



A second stage was a study of the effect of 

 the oxidation state of the heme pigments on 

 their ability to form ferrohemochromes. A 

 model system was developed using hemopro- 

 teins denatured by a detergent, Dupanol. The 

 surprising result was that both the oxidized and 

 the reduced pigments form the denatured hemi- 

 chrome (oxidized form) . However there is 

 some doubt that this model system resembles 

 closely the in vivo conditions, and better alter- 



natives are being devised. Further stages of 

 this work will concern the effect of denatura- 

 tion of heme pigments on their ability to form 

 hemochromses and the factors influencing the 

 stability of the hemochromes. 



Barrett et al. (1965) and our laboratory also 

 indicated that the final color of canned tuna 

 could be correlated with the amount of water- 

 extractable heme pigments present before can- 

 ning, and to a lesser extent with the shift of 

 the Soret peak from 412 m^a for oxymoglobin 

 to 406 m^ for metmyoglobin, the oxidized form. 

 This methodology did not prove entirely satis- 

 factory and was abandoned because the heme 

 pigments undergo other independent complex 

 chemical reactions, thus adding other variables. 



Sugars, the secondary color factors in tuna. 



— In addition to the tuna color due to heme 

 compounds, the appearance of tuna is also af- 



10 



