Margrethe Esaiassen

Muscle Quality and Storage Stability of Farmed Cod (Gadus morhua L.) Compared to Wild Cod

Abstract Quality characteristics of farmed and wild cod were compared during ice storage by measuring pH, water content, water-holding capacity (WHC), trimethylamine oxide (TMAO), trimethylamine (TMA), aerobic plate count (APC), as well as numbers of H2 S-producing bacteria (SPB) and Photobacterium phosphoreum. pH and water content were higher in wild cod than in farmed cod. WHC were similar for both groups until the last sampling, where farmed cod had a significantly higher WHC than wild cod. The TMAO level in farmed cod was only 5–10% of that found in wild cod. APC increased more rapidly in wild cod than in farmed cod, resulting in a 2 log units difference at the end of the storage period. P. phosphoreum were found in higher numbers in wild cod than in farmed cod, and SPB were not detected in farmed cod. These results might indicate that farmed cod have a slightly longer shelf life than wild caught cod.

ISOLATION AND SUBSTRATE SPECIFICITIES OF FIVE CHITINASES FROM THE HEPATOPANCREAS OF NORTHERN SHRIMP, PANDALUS BOREALIS

Abstract Five enzymes designated chitinase I, IIa, IIb, III, and IV have been isolated from the hepatopancreas of Pandalus borealis in a procedure including column chromatography on Q-Sepharose, Sephacryl S-200, phenyl-Superose and Superdex 75. The isolated enzymes were analysed by SDS PAGE. Chitinase I, III, and IV gave only one major band corresponding to 54–55 kDA. Chitinase IIa showed one major band at 61 kDA and two diminutive bands at 17 and 55 kDa, while chitinase IIb gave two major bands at 17 and 44 kDa. Estimated by gel filtration, the native molecular weights of chitinase I, IIa, IIb, III, and IV were 61, 69, 39, 57, and 54 kDa, respectively. The substrate and reaction specificities of the isolated chitinases were investigated, and the results show that the isolated enzymes are true chitinases. They do not hydrolyse N,N′-diacetylchitobiose or p-Nitrophenyl-N-acetyl-β-D-glucosaminide, but express activities when longer chitooligosaccharides or nitrophenylated chitooligosaccharides are used as substrates. Chitinase I and IIa gave an initial random cleavage pattern and might be classified as endochitinases, while chitinase III and IV released dimeric units from the substrates and might be termed chitobiosidases.

Purification and some properties of two β-N-acetylhexosaminidases from the hepatopancreas of Northern shrimp, Pandalus borealis

Abstract 1. 1. Two β-hexosaminidases were obtained from the hepatopancreas of the Northern shrimp Pandalus borealis by ion-exchange chromatography, gel filtration and hydrophobic interaction chromatography. According to the substrate specificities, both enzymes are β-N-acetylhexosaminidases (EC 3.2.1.52), designated forms I and II. 2. 2. The two enzyme forms have an absolute requirement for the N-acetylated sugar moiety and the β-glycosidic linkage, and showed no significant difference in the preference for the 4-C-epimer of glucose over galactose. 3. 3. Form II is more efficient hydrolyzing the di-, tri- and tetramer of N- acetyl-β- d -glucosamine than form I. 4. 4. β-N-Acetylhexosaminidase form I has a slightly lower pH-optimum than form II.

Effects of Long-Term Feed Deprivation on the Development of Rigor Mortis and Aspects of Muscle Quality in Live-Stored Mature Atlantic Cod (Gadus Morhua L.)

ABSTRACT Fresh Atlantic cod is available in large amounts in Norway during the first 5 months of the year. Live-storage of cod may extend the marketing period of fresh cod products throughout the year. In addition, this concept makes pre-rigor processing possible. The main problem of keeping wild cod in captivity is that it does not easily accept formulated dry feed. The purpose of this study was, therefore, to investigate how long-term live-storage of mature Atlantic cod in the absence of feed (79 days) affects the onset and development of rigor mortis, as well as fillet quality by assessing hardness and water-holding capacity of the muscle, pH, protein, and water content. The results showed that starvation of Atlantic cod for 23 days reduces the pre-rigor time from 29 to 17 h. Further starvation did not decrease this period significantly, suggesting that live-stored cod deprived of feed for 79 days may still be industrially processed before the onset of rigor mortis. More than 51 days of starvation reduced protein concentration and increased water content of the muscle. After 51 days, the muscle texture was softer than in fish starved for a shorter period.