WALLEYE POLLOCK, THERAGRA CHALCOGRAMMA: PHYSICAL, 



CHEMICAL, AND SENSORY CHANGES WHEN HELD IN ICE AND 



IN CARBON DIOXIDE MODIFIED REFRIGERATED SEAWATER 



Kermit D. Reppond, Fern A. Bullard, and Jeff Collins' 



ABSTRACT 



Walleye pollock. Theragra chalcogramma , were held in the round in ice and in CO2 modified refriger- 

 ated seawater and periodically examined for physical and chemical changes as well as changes in the 

 palatability of baked portions of blocks of fillets- Taste panel evaluation revealed that satisfactory 

 fillets were obtained from fish that would have been judged spoiled if based on examination of the fish in 

 the round. Sensory evaluation of baked fillet portions indicated that fish were acceptable for consump- 

 tion to 6 days if heavily iced. The fish held in modified refrigerated seawater were judged acceptable 

 only to 4 days because of lower sensory scores for salt content and flavor. Yield of fillets and protein 

 content did not change significantly with time of holding m either medium. The total volatile acid and 

 trimethylamine data indicated that these tests may prove useful as chemical indicators of spoilage for 

 ice-held fish whereasdetermination of trimethylamine oxide or extractable protein nitrogen may prove 

 useful for fish held in modified refrigerated seawater. Round weight and dimethlyamine content 

 increased in fish from both systems with time of holding as did the salt content offish held in modified 

 refrigerated seawater. Total volatile base, formaldehyde, and free c«-amino-nitrogen content remained 

 unchanged but nonprotein nitrogen and total sil-.ds content decreased with time of holding. 



Walleye pollock. Theragra chalcogramma, have 

 been the subject of several studies concerning 

 changes that occur in frozen storage, and how 

 these changes affect the suitability of pollock in 

 traditional Japanese products (Iwata and Okada 

 1971, Okada and Noguchi 1974). Uchiyama et al. 

 (1972) and Kramer et al. (1977) reported on 

 changes that occur when pollock are held in ice. If 

 pollock are to be held more than a few hours, ice or 

 some type of refrigeration is needed to retard de- 

 terioration in quality. The advantages and disad- 

 vantages of refrigerated seawater (RSW) for hold- 

 ing fish and shellfish are well established (Roach 

 et al. 1967). In recent years, reports have appeared 

 on holdmg fish or shrimp in RSW modified by the 

 addition of dissolved CO2 (MRSW) (Bafnett et al. 

 1971: Bullard and Collins 1978). These authors 

 reported that deterioration occurred at a slower 

 rate in MRSW than in ice. Lemon and Regier 

 (1977) noted similar results with Atlantic mac- 

 kerel. Stow ier scombrus, held in either ice, RSW, 

 or MRSW. Experiments with Atlantic ocean 

 perch, Sebastes marinus. (Longard and Regier 

 1974) also confirmed the superiority of MRSW 

 over RSW or ice as a holding medium. The objec- 



'Northwest and Alaska Fisheries Center. National Marine 

 Fisheries Service. NOAA, P.O. Box 1638. Kodiak. AK 9961.5. 



tives of this study were to generally characterize 

 the changes that occur in walleye pollock with 

 time of holding in ice and in MRSW, to determine 

 which holding medium is superior, and to deter- 

 mine if some of the common chemical indices for 

 spoilage could be useful for pollock. 



METHODS 



Sampling 



A catch of various species of bottom fish includ- 

 ing approximately 135 kg each of walleye pollock 

 and Pacific cod, Gadus macrocephahis, was made 

 on 2 November 1976 by the RV Oregon near Cape 

 Barnabas, Kodiak Island, Alaska, and shall be 

 referred to as Lot 1. Lot 1 was evaluated by physi- 

 cal and chemical methods and by informal subjec- 

 tive observation on whole fish and their raw fillets. 

 No formal sensory evaluation of cooked pollock 

 was possible because of the limited amount offish. 

 To obtain fish for formal sensory evaluation, a 

 second catch was made 1 yr later on 13 October 

 1977 at the same location and shall be referred to 

 as Lot 2. Most of the chemical analyses conducted 

 on Lot 1 were repeated on Lot 2 to see if the lots 

 were similar. Analyses for total volatile base 

 (TVB) and free a-amino acids were conducted on 



Manuscript accepted December 1978 

 FISHERY BULLETIN; VOL. 77. NO 2, 1979. 



481 



