xanthine oxidase followed by 1 min bubbling 

 of air through the solution. The shift in op- 

 tical density in the neutralized extracts when 

 treated with xanthine oxidase was then com- 

 pared to this value (0.08 OD = ly of Hx) . An 

 aliquot of the neutralized extract was read at 

 248 m/i, then shaken with Dowex 1x8 (chlor- 

 ide) resin to remove the nucleotides, and read 

 again at the same wavelength (Jones and Mur- 

 ray, 1964) . The difference in the readings was 

 taken as an estimate of inosinemonophosphate 

 (IMP) since this author and others have ob- 

 served that IMP is the only nucleotide of con- 

 sequence remaining shortly after death. The 

 reading of the extract after resin treatment 

 was taken as an estimation of inosine and Hx. 

 The Hx was subtracted leaving an estimation 

 of inosine. 



Twenty grams of canned product from each 

 fish was ground with 0.6N HCIO4 as described 

 above. All analyses run above were deter- 

 mined on this extract in the same manner. All 

 determinations on the raw tuna muscle were 

 run in duplicate for each individual fish. The 

 results for each fish in each treatment were 

 averaged and are so reported. The determina- 

 tions on the canned product were run in dupli- 

 cate on the combined extracts for each treat- 

 ment. 



Organoleptic Evaluation 



The taste panel description is given in Table 1 

 as used and reported previously by Crawford 

 et al. (1968, 1969, 1970). The canned tuna 

 samples were allowed to stand for at least 4 

 weeks before they were examined by an expert 

 panel of judges. In this analytical panel, the 

 judge was not asked to assess preference but 

 to give a sensory description of the prod- 

 uct. 



RESULTS AND DISCUSSION 



Glycolytic Degradation Products 

 (Table 2) 



Total reducing sugars, /xM/g. — The total 

 reducing sugars (TRS) determined on the raw 

 muscle and canned product was calculated as 



fiu/g of glucose. The content varied from 5 

 to 31 ixu/g. The results from the different 

 groups were as follows: 



The rested controls that were sampled and 

 canned immediately were higher in TRS con- 

 tent than the corresponding stressed controls 

 for each treatment. However, when frozen, 

 the stressed controls had a higher content. 



Although this observation is consistent with 

 the need for more energy during stress, no val- 

 id conclusions can be drawn from these obser- 

 vations because the test employed will deter- 

 mine glycogen content as well. Glycogen is not 

 quantitatively extracted with the method used. 

 However, this test does give an estimate of the 

 total carbohydrate content and is used some- 

 times in canneries with some degree of success 

 as a guideline in selecting raw material for 4-lb. 

 institutional packs. These packs, because of 

 their size, are retorted at high temperatures 

 for long periods of time, thus giving full op- 

 portunity for browning reactions. Consider- 

 ation of the scores for scorch in Table 4 would 

 seem to invalidate this procedure since there 

 was marked evidence of scorch in almost all 

 cans for all treatments regardless of the TRS 

 content. But, it may be reasoned that since 

 the fish delivered to the canneries are usually 

 several weeks old, there is probably very little 

 glycogen remaining. (The temperature at 

 which tuna is stored on the vessels, about 20° F, 

 is not suflicient to stop glycolysis.) Therefore, 

 the TRS content of this fish should contain very 

 little glycogen and mostly carbohydrate that 

 can be involved in browning reactions, e.g., 

 glucose phosphate, fructose phosphate, glucose, 

 and ribose. 



The TRS content of the can, with only two 

 exceptions, showed lower values than the cor- 

 responding raw material. This is consistent 

 with the concept of sugar-amino reactions 

 (Maillard reaction) in browning. The rested 

 fish when frozen after holding showed a lower 

 TRS content than the unfrozen for all temper- 

 atures including the controls. This is also true 

 of the stressed fish except those held for 6 hr 

 in 78° F refrigerated seawater (RSW) where 

 the values are nearly the same. These obser- 

 vations indicate that freezing may retard gly- 

 coneogenesis and suggest that glyconeogenesis 

 does indeed occur at least during these time 

 intervals postmortem. 



15 



