their experience had formed the basis of scor- 

 ing systems generally used by canners. The 

 second was the letters of complaint received 

 from consumers, which letters, although rel- 

 atively few in number, reflect points which may 

 be critical to acceptance. 



Finch (1967a, 1967b) and Crawford et al. 

 (1970) reported some of the difficulties in as- 

 sessing the quality of tuna. It was pointed out 

 that the literature to date on tuna technology 

 offered very little useful information although 

 they have reported various aspects of composi- 

 tion and changes in tuna. Finch and Crawford 

 et al. also pointed out some of the factors that 

 affect the quality of tuna: 



Physical Characteristics: The size of the 

 tuna is important because the larger the fish, 

 the longer it takes to chill, freeze, and cook; 

 these longer times may alter some quality pa- 

 rameters, such as color, scorch, and texture 

 (Barrett et al., 1965). The differences in spe- 

 cies contributes to differences in color: for 

 example, albacore has less heme pigments than 

 skipjack and is therefore naturally lighter in 

 color. 



Catching and Handling: The premortem 

 conditions have long been known to effect the 

 postmortem chemistry and quality of fish. Fish 

 caught by methods that allow long periods of 



struggle and stress before death have low pH, 

 glycogen content, etc., all of which affects the 

 quality of the finished canned product. 



Trawl-caught halibut produces a low pH that 

 causes the edible flesh to appear "chalky" 

 whereas longline halibut has a higher pH and 

 less incidence of chalkiness (Spinelli, unpub- 

 lished). Longline tuna often has a higher pH 

 than seined tuna which leads to the formation 

 of struvite (harmless glasslike crystals of mag- 

 nesium ammonium phosphate that form in the 

 can after processing). The canned products 

 of seined fish, on the other hand, are generally 

 darker, tougher in texture, flake more readily, 

 and show more evidence of bruises, which ap- 

 pear as dark-pigmented "stains." 



Other aspects that affect quality such as 

 chilling, freezing, and thawing will be discussed 

 later. 



Based upon these factors and with the help 

 of industry technologists, scales of quality have 

 been worked out which can be used for judging 

 the effects that various experimental condi- 

 tions, such as difl'erent freezing methods, have 

 on the canned product (Crawford and Finch, 

 1968; Crawford et al., 1969). A trained taste 

 panel examines the sample and gives it a series 

 of scores as shown in Table 1. (Sometimes in 

 special tests other factors such as blood spots 



Table 1. — Organoleptic scoring system for canned tuna. The can is opened and turned 

 out carefully onto a white enamelled surface for examination. 



