Contact
Kolbrún Sveinsdóttir
Project Manager
kolbrun.sveinsdottir@matis.is
Development of Quality Index Method and shelf life of thawed mackerel (Scomber scombrus) / Development of Quality Index Method and storage life of thawed mackerel (Scomber scombrus)
The QIM method (Quality Index Method) is an objective, fast and reliable sensory evaluation method that has been developed to assess the freshness of fish. The aim of the study was to prepare a QIM rating scale for thawed mackerel (Scomber scombrus) stored in ice at 0 ° C and to test its use in a shelf life test. The mackerel was evaluated by sensory evaluation according to QIM and DA method (generic descriptive analysis), microorganisms (TVC and H2S producing) were also counted and histamine was measured for up to 9 days after thawing. The result of the study was the QIM method for thawed mackerel which was developed and tested in a shelf life test. Quality factor - QI (total grade) increased linearly with ice shelf life. The QIM method for thawed mackerel is based on an assessment of quality factors such as the appearance of redness, texture, color and shape of the eyes, the color and odor of the gills, the appearance of mucus in the gill and gill leaf and the intestinal dissolution, and the total fish can reach a maximum of 19. The project also developed a method (general descriptive analysis-DA) for evaluating boiled mackerel. The main characteristics of the mackerel immediately after thawing were the smell and taste of fresh oil, the smell of metal and the sweet smell / taste that faded with the storage period. What limited the shelf life were sensory properties that describe the symptoms of damage, such as the stench and taste that can be noticeable in fatty fish after prolonged cold storage. According to a sensory assessment of boiled mackerel fillets, the shelf life of thawed mackerel after five months of cold storage is about 4-6 days. The total number of micro-organisms and H2S-producing micro-organisms was lower than is usually seen at the end of the shelf-life of micro-organisms. Histamine was not detected (<5 ppm) in thawed mackerel during the 9-day ice-storage period.
The Quality Index Method (QIM) is an objective, rapid and reliable sensory method. The aim of the present study was to develop a QIM scheme for frozenthawed Atlantic mackerel (Scomber scombrus) stored in ice at 0 ° C and evaluate the scheme in a shelf life study. The mackerel was evaluated with sensory evaluation (QIM and generic descriptive analysis (DA)), microbial counts (Total viable counts (TVC) and H2S-producing bacteria) were estimated and histamine measured for up to nine days. The main result of this study vas the QIM scheme to evaluate freshness of frozen-thawed Atlantic mackerel storage in ice which was developed and tested in a shelf life study. The quality index - QI (sum of scores) increased linearly with storage time on ice. The QIM for thawed mackerel is based on the evaluation of quality parameters dealing with the appearance on back and belly side, texture, color and shape of eyes, mucus, color and odor of gills and appearance of gill filaments and dissolution of viscera. The maximum sum of scores (QI) can be 19. A method to evaluate cooked mackerel was also developed (general descriptive analysis-DA). Newly thawed mackerel had fresh oil, metallic and sweet odors and flavors. The main limitation of shelf life in chilled storage after thawing were sensory characteristics describing spoilage such as rancid odor and flavor which can be prominent in fatty fish species after extended frozen storage. According to sensory evaluation of cooked mackerel, the shelf life of thawed mackerel after five months of frozen storage is around 4-6 days. Counts of TVC and H2S producing bacteria were relatively low at the end of shelf life. Histamine was not detected (<5 ppm) in the thawed mackerel during the storage time of nine days on ice.
