BLACK ROCKFISH, SEBASTES MELANOPS: CHANGES IN PHYSICAL, 



CHEMICAL, AND SENSORY PROPERTIES WHEN HELD IN ICE AND 



IN CARBON DIOXIDE MODIFIED REFRIGERATED SEAWATER 



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



ABSTRACT 



The purpose of this study was to determine changes in various properties of fillets, minced flesh, and 

 washed minced flesh from black rockfish, Sebastes melanops, as affected by time of holding in ice or 

 carbon dioxide modified refrigerated seawater and frozen storage at  18° C , Fish were held up to 14 days 

 in the holding mediums and removed periodically and analyzed for changes in physical , chemical, and 

 sensory properties. The yield of fillets calculated from the initial whole weight was unaffected by time 

 of holding in either system. Subjective observations made during the holding periods indicated that 

 fillets of good quality could be prepared from rockfish held for 10 days in either system. These 

 observations were confirmed in a later series by sensory evaluation of cooked portions from the frozen 

 blocks of fillets prepared at intervals during an 11-day holding period. The chemical analyses for 

 trimethylamine, total volatile acid, and total volatile base were of no use to measure spoilage. Washing 

 the minced flesh resulted in a reduction of solids, trimethylamine oxide, and salt and a reduction in 

 yield when expressed on a salt-free constant, l&^c solids basis. The extractable protein nitrogen of 

 minced flesh decreased with time of frozen storage at -18° C and was strongly influenced by the length of 

 holding period for the fresh whole fish. 



Several papers have been published on the fresh or 

 frozen characteristics of fillets or minced flesh 

 from rockfishes. Different species of rockfishes 

 gave products having different fresh acceptability 

 and frozen storage life (Miyauchi and Stansby 

 1952). Stansby and Dassow (1949) found that the 

 frozen storage quality of fillets from yellowtail 

 rockfish, Sebastes ftavidus, could be improved by 

 removing part of the dark flesh along the lateral 

 line. Barnett et al. (1971) compared yellowtail 

 rockfish held in refrigerated seawater (RSW) and 

 RSW modified with the addition of CO2 (MRSW). 

 The fresh storage life was extended 1 wk in MRSW 

 over RSW. Teeny and Miyauchi (1972) increased 

 the frozen life of minced flesh of yellowtail rockfish 

 and silvergray rockfish, S. brevispinis: by using 

 various additives. Additional improvements in 

 storage life were obtained by washing the minced 

 muscle of black, silvergray, and yellowtail 

 rockfishes (Miyauchi et al. 1975.) 



The objectives of this study were generally to 

 characterize and compare the changes that occur 

 in black rockfish with time of holding in ice and in 

 MRSW, to determine sensory properties of fillets 

 as affected by fresh holding time, and to determine 



'Northwest and Alaska Fisheries Center, National Marine 

 Fisheries Service, NOAA, P Box 1638, Kodiak, AK 99615. 



Manuscnpt accepted April 1979 



FISHERY BULLETIN VOL 77, NO. 4, 1980. 



the changes in amine content and extractable pro- 

 tein nitrogen with time of frozen storage of washed 

 and unwashed minced flesh. 



EXPERIMENTAL PROCEDURES 



Sampling 



Two groups offish were used in this study. Lot 1 

 was used to determine physical and chemical 

 properties and Lot 2 was used for formal sensory 

 evaluation. The fish were caught over a 2-h period 

 with hook and line, with or without bait. These 

 fish are found locally on exposed, highly sloped 

 rocky shores with strong currents where trawling 

 gear cannot be used. A sporadic local fishery has 

 employed the same fishing technique. Lot 1 fish 

 (154 fish, 265 kg, 0.2 kg SD) were captured 2 July 

 1977 at the Triplets, 20 mi northwest of Kodiak, 

 Alaska, and delivered to the laboratory about 2 h 

 later. The fish were individually tagged and 

 weighed before placing in the previously de- 

 scribed ice and MRSW holding systems (Bullard 

 and Collins 1978). The raw fish handling and sam- 

 ple preparation were similar to that previously 

 reported for walleye pollock (Reppond et al. 1979), 

 and are briefly described here. Fish were sampled 

 according to weight classes to give an average of 



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