NATURE OF GREEN OR OFFCOLOR CONDITION 

 IN PRECOOKED YELLOWFIN TUNA 



By 



John J. Naughton 

 Michael M. Frodyma 



Harry Zeitlin 

 Chemistry Department 

 University of Hawaii 



The color of foodstuffs is of te n an 

 important factor governing their acceptance or 

 rejection by the processor and consumer. An 

 interesting example of the influence of color in 

 this regard is the "greening" of the flesh of cer- 

 tain tuna that becomes evident on precooking 

 prior to canning. The exploration of the fishery 

 resources of the central Pacific by the Pacific 

 Oceanic Fishery Investigations of the U. S. Fish 

 and Wildlife Service, and the use of the longline 

 to catch large deep-swimming yellowfin tuna, 

 Neothunnus macropterus (Temminck and 

 Schlegel), have drawn attention to this particu- 

 lar color problem because of the relatively 

 large percentage of tuna prone to "greening" 

 in the catch made by this type of gear. 



The Japanese have long recognized the 

 problem, particulary in their winter catch of 

 albacore, Germo alalunga (Bonnaterre), in the 

 North Pacific and have given some study to its 

 cause. The conclusions reached as a result of 

 their investigations are that greenness is asso- 

 ciated with low oil content, with low weight-to- 

 length relationship, and is a physiological con- 

 dition unrelated to freshness. Some of these 

 investigators feel that the wasting effects of 

 the struggles of the fish endeavoring to free 

 themselves from the hook in the longline method 

 of fishing have much to do with the discoloration 

 subsequently encountered (Miyauchi 1950). 



More recently certain Japanese investiga- 

 tors have reported a correlation between the 

 greening of tuna and the concentration of a flesh 

 pigment spectrophotometrically identified by 

 them as myoglobin. They also claim to be able 

 to predict the occurrence of greening with 85 

 percent certainty by visual exannination of the 

 raw meat (Matsuzaka and Takahashi MS.). 



It is the purpose of this report 

 to summarize the conclusions reached as a 

 result of a preliminary investigation on this 

 problem conducted at the University of Hawaii 

 during 1955-56 under contract No. 14-19-008- 

 2318 with the Pacific Oceanic Fishery Investi- 

 gations. We are indebted to Mr. Fred Jermann 

 of Hawaiian Tuna Packers, Ltd., Honolulu, for 

 assistance in preparing sannples in the cannery 



and for other services that have contributed to 

 the study. Thanks are also due to Dr. Albert 

 L. Tester, Director, and Mr. Garth I. Murphy, 

 Assistant Director of the Pacific Oceanic Fish- 

 ery Investigations, and to other members of 

 the staff for help and suggestions in this work. 



COLOR IN FOODS 



The problem of the definition and specifi- 

 cation of color is a highly complicated one, 

 the detailed discussion of which would be out 

 of place here. Suffice it to say that physio- 

 logical as well as physical factors are involved. 

 In other words, the "properties" of the obser- 

 ver must be considered as well as the spectral 

 distribution at the source of color. Many sys- 

 tems (C.I.E,, Munsell, U.S.C., for example) 

 have been set up and many instruments devised 

 to facilitate an objective definition of color. It 

 has been recognized, however, the the spec- 

 trophotonnetric curve, the plot of reflected or 

 transmitted intensity versus wave-length, is 

 "the most unambiguous specification of color 

 that can be obtained, " and that the spectropho- 

 tometer is the basic instrument in the standardi- 

 zation of color (Mackinney and Chichester 1954), 

 Recognition should be made of the limitations of 

 such curves in the evaluation of color as it will 

 appear to the eye since perceived color can be 

 greatly altered by slight variations in spectral 

 curves, and two different curves may give the 

 same color response to the eye. In addition to 

 .the dominant wave-length (hue), the factors of 

 whiteness-purity (chroma) and photometric 

 brightness (value) are also to be considered in 

 color specification. 



THE COLOR OF NORMAL AND GREEN TUNA 



In studying the color problem in tuna flesh 

 it was necessary to establish objectively the 

 normal color of desirable or acceptable meat. 

 Accordingly precooked meat judged to be of 

 good quality was selected and designated as 

 normal. In order to define objectively the 

 color of this meat, it was decided to measure 

 its reflectance over the visible range of 



