FISHERY BULLETIN VOL 77. NO 2 



4 6 8 



TIME OF HOLDING DAYS 



FIGURE 3.— Change in trimethylamine oxide iTMAOl content of 

 fillets from walleye pollock I Lot 2) with time of holding in ice and 

 in modified refrigerated seawater iMRSW). 



4 6 8 10 



TIME OF HOLDING DAYS 



FIGURE 4.— Change in dimethylamine iDMAl content of fillets 

 from walleye pollock iLot 21 with time of holding in ice and in 

 modified refrigerated seawater (MRSWl. 



was linear and equal in both systems and there- 

 fore had little usefulness as an index of spoilage. 

 Because of the leaching ability of both the melt 

 water in the ice system and the brine in the MRSW 

 system, the rate of accumulation of DMA in the 

 flesh may be different from the rate of formation of 

 DMA. In the dissociation of TMAO, FA should be 



formed in equal molar proportion to DMA. The 

 results for analysis for FA in fish from Lot 2 re- 

 vealed that FA content was 4 ppm in both systems 

 and did not change with time of holding. The lack 

 of an increase in FA content was probably due to 

 its reaction with proteins. Castell et al. (1973) 

 noted that addition of FA lowered the solubility of 

 the protein so the formation of FA can be inferred 

 by a decrease in EPN with time of holding (Figure 

 5). 



Results from an experiment on a control sample 

 to which NaCl was added indicated that the low 

 EPN values of MRSW-held fish were not due to 

 their high salt content. Like the TMAO content, 

 the values for EPN are about the same for either 

 holding system until after 4 days when the values 

 for MRSW-held fish decreased rapidly (Figure 5). 

 Data from fish in Lot 1 also indicated that there 

 was a similar difference in solubility after 4 days 

 of holding. Although there was no significant 

 statistical correlation among EPN values, TMAO 

 content, or the flavor scores, all three of these 

 experimentally determined values decreased at 

 the same time in fish held in MRSW, i.e., after 4 

 days. With ice-held fish, the decrease in flavor 

 preceded the decrease in TMAO and there was no 

 decrease in EPN values. Evidently, analysis for 

 TMAO and EPN may provide and index of spoil- 

 age for MRSW-held fish but not for ice-held fish. 

 Tokunaga (1964) reported data similar to that 



4 6 8 



TIME OF HOLDING DAYS 



Figure 5.— Change in extractable protein nitrogen (EPNl of 

 fillets from walleye pollock I Lot 2) with time of holding in ice and 

 in modified refrigerated seawater I MRSW). 



486 



