Freezing and thawing process (atcharaporn khoomtong)


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Freezing and thawing process (atcharaporn khoomtong)

  1. 1. ByMs.Atcharaporn Khoomtong
  2. 2. Content Introduction Fish muscle Fundamentals of Freezing and Thawing of fishes and seafood Quality-related changes in frozen fish muscle The length of storage time for fish 2
  3. 3. Know about fish Pelagic fish are fish that live in surface / center, not at the bottom, generally consisting of small-sized fish such as anchovies, mackerel, and other screens. 3
  4. 4. Know about fish (Cont’) Demersal fish, such as cod, haddock and pollock, and flatfishes live near or at the bottom of the seas. They feed mostly on other fish and organisms. 4
  5. 5. Fish muscle Major composition 5
  6. 6. Let you know about TMAO TMAO is formed by biosynthesis in certain zooplankton species. These organisms possess an enzyme (TMA mono-oxygenase) which oxidizes TMA to TMAO. TMA is commonly found in marine plants as are many other methylated amines (monomethylamine and dimethylamine). 6
  7. 7. Structure of fish muscle Fish muscle is composed of striated muscle fibers arranged in a parallel, longitudinal shape. Fish has muscle cells running in parallel and connected to sheaths of connective tissue (myocommata), which are anchored to the skeleton and the skin. The bundles of parallel muscle cells are called myotomes 7
  8. 8. Post mortem changes in fish muscle Directly after death of the fish, a series of biochemical reactions starts, which is importance for the quality and shelf life of products. It’s depend on The type of fish species, The physiological condition of the fish, The environmental influences (for example water temperature, salinity) the living fish 8
  9. 9. Catch-bleeding-guttingSensory changes Post-mortem changes FRESH Blood circulation stopsbiochemical reactions Glycogen Lactic acid ATP falls pH falls AUTOLYSIS Rigor mortis Enzymes activated Resolution of rigor and FLAT autolysis Microbial spoilage SWEET/STALE Microorganisms PUTRID Lipid oxidation Spoilage Source from, Huss (1995) 9
  10. 10. Freezing and Thawing of fishes 10
  11. 11. Fundamentals of Freezing of fishesGeneral Freezing temperature  Use temperature < 32 F (0 C)  Change in water from liquid to solid. General Freezing theory  lower temperature. Will reduce spoilage.  Water is unavailable for microorganisms and chemical reactions. 11
  12. 12. FREEZING/SUPERFREEZING OF FISH Freezing is the process by which temperatures of fish or seafood are reduced to -20oC Super freezing is the process by which temperatures of fish are mechanically reduced to -40oC 12
  13. 13. Freezing point depression In fish muscle the freezing point is depressed below that of pure water because of small solutes present in the muscle water. The freezing point is often referred to as ‘the equilibrium freezing point’ 13
  14. 14. Ice crystal formation in pre- and post-rigor muscle In pre-rigor muscle, the cell fluids are associated to intra-cellular proteins and the diffusivity from inside to outside the cell is therefore limited resulting in the formation of the intracellular ice crystals independent of freezing rate. If very slow freezing rates are used the muscle can go into rigor mortis during the freezing process, and ice crystal formation will then be extra-cellular (Love, 1970). 14
  15. 15. Fundamentals of Thawing of fishes Thawing is the process of changing the state of a product from frozen to unfrozen. It involves transferring “heat” to a frozen product to melt the ice that was formed within the flesh during the freezing process. Like freezing, thawing should be carried out as quickly as possible to maintain the quality of the product. 15
  16. 16. Fundamentals of Thawing of fishes If the thawing process is carried out correctly there should be little effect on the quality of the product. The final quality of thawed seafood will depend not only on the thawing process but also on factors such as frozen storage conditions and the length of time that it has been frozen, packaging, product form and product type. 16
  17. 17. Over Thawing Under ThawingThe flesh may soften Fish may be difficult & discolor or dangerous to fillet Poor filleting will Loss of flavor result in a lower yield Lower yield Possible growth of bacteriaPossible increase in enzyme spoilage 17
  18. 18. Quality-related changes in frozen fish muscle 18
  19. 19. A mistake that many people make when freezing fish and other seafoodproducts is to assume that, once it hasbeen frozen, it will not change. 19
  20. 20. The quality of frozen fish or seafood is directly related to the quality of the starting material.
  21. 21. If the seafood you freeze is of poor quality, theseafood you thaw will be of poor quality or evenpoorer.
  22. 22. Care should be taken to ensure that only high-quality fish are considered for freezing.
  23. 23. Factors that effected on Quality-related changes in frozen fish muscle Fish species Temperature and Handling before slaughter Slaughter stress Temperature of the pre-rigor storage Freezing rate Frozen storage temperature and time Thawing procedure Prevention against oxidation (light,oxygen) (Sørensen et al., 1995) 23
  24. 24. Affecting protein changes in fish muscleDehydration and the effect of inorganic salts Changes in lipids and fatty acids Enzymatic breakdown of TMAO (Autolytic changes) 24
  25. 25. Summarize of Protein denaturation (Love, 1970) 25
  26. 26. Changes in lipids and fatty acids Oxidation of unsaturated fatty acids or triglycerides in fish results in the formation of free radicals produced through decomposition of lipid hydroperoxides via a free- Off flavors radical mechanism. and ordors Mackie, 1993 26
  27. 27. Enzymatic breakdown of TMAO (Autolytic changes) Fishes, like cod, hake (Merluccius spp.) or Alaska pollack (Theragra chalcogramma), contain the enzyme trimethylamine oxide demethylase (TMAOase), which catalyses the cleavage of trimethylamine oxide (TMAO) into dimethylamine (DMA) and formaldehyde (FA). 27
  28. 28. Changes in functional properties caused by protein changes The main changes are reported to occur in myosin light-chain, but actin and actinin also degrade during frozen storage. Some of the changes reported are increases in ß-sheet at the expense of -helix structure. As the main part of muscle water is located within the myofibrillar structure, changes in this typically result in reduced WHC. 28
  29. 29. Reasons for Quality Loss in Frozen Fishery Products during StorageSource from, Huss (1995) 29
  30. 30. The length of storage time for fish in a freezer depends  Fish species  On storage temperature,  Temperature fluctuations in the freezer,  Method of packaging and packaging materials,  Moisture and fat content of the fish and  The condition of the fish at the time of freezing. 30
  31. 31. Conclusion The quality of fishery products is influenced by both intrinsic and extrinsic factors. Species, size, sex, composition, toxins, contamination with pollutants, and cultivation conditions are the factors responsible for changes in intrinsic quality. The biochemical characteristics of fish muscle such as low collagen, comparatively higher contents of unsaturated lipids as well as soluble nitrogen compounds influence autolysis, rapid microbial proliferation, and spoilage. Low-temperature processing, including freezing, is probably the most widely used method to slow safety and quality deterioration of aquatic foods. 31
  32. 32. References Aubourg, S.P. and Medina, I. (1999). Journal of the Science of Food and Agriculture, 79(13):1943-1948. Cappeln, G., Nielsen, J., and Jessen, F. (1999). Journal of the Science of Food and Agriculture, 79(8): 1099-1104. Huss, H.H.(1995).Quality and quality changes in fresh fish.FAO Fisheries Technical paper 348. Rome,Italy.195 p. …..ETC……. 32