Collagen in the muscles of fish constitutes the main component of the connective tissue membranes joining individual myotomes and is responsible for the integrity of the fillets. The content of collagen in fish muscles is from about 0.2 to 1.4% and in squid mantel about 2.6%. Fish and invertebrata collagens contain slightly more essential amino acids than intramuscular bovine connective tissue collagen. The invertebrata collagens are exceptionally rich in sugars linked mainly O-glycosidically to hydroxylysine residues. During maturation of fish the proportion of collagen to total protein in the muscles increases while the extent of crosslinking does not change significantly. The thermal properties of fish collagens depend significantly on the content of hydroxyproline and proline residues which in turn is correlated to the temperature of the habitat. Generally the shrinkage temperature of fish skin collagens is about 20 degrees C lower than that of mammalian hide collagens. In several species of fish the weakening of the connective tissues post mortem may lead to serious quality deterioration that manifests itself by disintegration of the fillets, especially under the strain of rough handling and of rigor mortis at ambient temperature. Thermal changes in collagen are the necessary result of the cooking of fish, squid, and minced fish products and contribute to the desirable texture of the meat. However, they may lead to serious losses during hot smoking due to a reduction in the breaking strength of the tissues when heating is conducted at high relative humidity. Because of the high viscosity of gelatinized collagen, it is not possible to concentrate the fish stickwaters, a proteinaceous byproduct of the fish meal industry, to more than 50% dry matter. Better knowledge of the contents and properties of fish collagens could be helpful in rationalizing many aspects of fish processing.

Physical, sensory, microbiological and chemical analyses were carried out on jack mackerel during 23 days of storage in ice. Sensory results indicate that jack mackerel used in this trial had a shelf-life of 7 days. Aerobic plate counts never exceeded 106/g flesh during the first 11 days. The K value reached 20% after 7 days. Trimethylamine, total volatile base, pH and thiobarbituric acid analyses were not good indicators of changes in quality during the shelf-life. Proximate analyses were carried out on representative samples of the fish.

Sensory, microbiological and chemical analyses were used to compare whole orange roughy stored in ice with headed and gutted orange roughy stored in ice. Sensory results indicated that the whole fish had a shelf-life of 11 to 13 days. Heading and gutting gave only a slight increase in storage life. Microbiological results suggested that this increase was not due to any reduction in bacterial activity. However, chemical analyses indicated that there was reduced autolysis in the headed and gutted fish. Sulfide producing bacteria were not a significant proportion of the spoilage flora. The K value and results of analyses of inosine 5'-monophosphate and inosine were consistent with the sensory results and therefore these chemical tests are considered useful for monitoring changes in the freshness of orange roughy during ice storage.

No abstract

Smooth ore0 dory (Pseudocyttus rnaculatus), a deep water fish, was monitored for changes during storage in ice. Based on the sensory evaluation of the cooked flesh the storage life was 8 days for acceptable quality fish.Bacterial counts of flesh and surface, the loss of inosine monophosphate (IMP) and the K value showed significant changes during the storage life. Therefore these were found to be useful for monitoring loss of freshness and development of spoilage. After 13 days there were off flavours in the cooked fish, dephosphorylation of IMP had levelled off, and the K value had reached 70%.The changes that occurred during storage of this deep water species in ice were similar to those changes commonly observed in demersal species from shallow temperate coastal waters. KeywordsDescriptive analysis, nucleotides, off-flavours, Pseudocyftus maculatus, sensory quality, TRA values. * Correspondent. Fax: +64 98 493660. Scott et al. 1984;Dhananjaya, et al., 1986). The proximate composition of ore0 dory has been reported by Vlieg (1983). Buisson el al. (1982) showed that, like orange roughy, ore0 dory has a high proportion of wax ester in the lipid fraction. D. N .The purpose of this study was to examine the sensory, chemical, and microbiological changes which occur during the storage in ice of whole smooth ore0 dory. Materials and methods Raw materials and samplingUndamaged smooth ore0 dory were selected from the net after a 1 h 30min tow on 19 March 1987 on board the F.V. Arrow (Sealord Products Ltd, Welson, New Zealand). The fish were caught in Area C on the northern edge of the Chatham Rise off the east coast of New Zealand at a depth of 1060 metres by bottom trawling. The water temperature at 1000 metres was 6°C and the surface water temperature was 18°C. The fish were at 16.5"C prior to icing. Over 100 kg of fish were packed in ice and landed at Nelson on the following morning.Six whole fish were used for proximate compositional analysis. Thirty-four fish were weighed, measured, sexed and processed to frozen shatter pack fillets within 8 h of landing. These were stored at -70°C as reference samples for sensory evaluation. After 1 day storage in ice five randomly selected fish were examined for raw sensory attributes, then sampled for pH, TBA number, and nucleotide analyses. The remaining fish were stored in a chiller under melting ice until required.Iced fish and reference fillets were sampled 4, 8, 11, 13, 15, and 18 days after capture. On each sampling occasion, 11 fish were randomly selected and analysed. Sensory evaluationRaw Jish. Five whole fish were evaluated by three people experienced in the description of raw fish quality. The resilience of the fish flesh was determined by finger pressure. The odour of the gills and the appearance of the skin, gills, eyes, and surface slime were also described.Cooked fish. The attributes of cooked smooth ore0 dory were evaluated by 17 -20 panellists who had been trained in the descriptive evaluation of fish (Scott & Hogg, 1985).Reference samples were thawed rapidly...