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Factors influencing storage & shelf life of fresh fish

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1 Factors influencing storage & shelf life of fresh fish
Quality and safety issues in fish handling ----- A course in quality and safety management in fishery harbours in Sri Lanka NARA, DFAR, ICEIDA and UNU-FTP Learning objectives After this lecture participants will be: - familiar with shelflife and factors affecting shelflife of fish raw materials. Icelandic International Development Agency (ICEIDA) Iceland United Nations University Fisheries Training Programme (UNU-FTP) National Aquatic Resources Research and Development Agency (NARA) Sri Lanka Department of Fisheries and Aquatic Resources (DFAR)

2 Factors affecting shelf life How to determine shelf life
Content What is shelf life Factors affecting shelf life How to determine shelf life The content of the lecture is about the shelf life, factors affecting shelf life and the methods to determine the shelf life.

3 Learning Objectives After this lecture participants will be familiar with: Shelf life and factors affecting shelflife of fish raw materials. some monitoring method to determine shelf life of fish

4 Shelf life Shelf life can be defined as the period of time that the fish is fit for consumption The limit of shelf life i.e. when the fish becomes unfit for consumption can be determined based on sensory, chemical or microbial criteria Time and temperature of storage can also be used as criteria to determine the limit of shelf life Quality parameter rather than a safety parameter Strongly underline and clearly explain the meaning of “fit for consumption” is safe for consumers and good quality. The criteria to determine the end of shelflife is different for different species Commercial partners in the chain have their own quality criteria to determine the end of shelf life based on the requirements of the respective customers. Shelf life is evaluated based on the fish sensory quality rather than safety level.

5 Factors affecting shelf life of fish
Composition Method of catching Post harvest treatment Processing (e.g. freezing, drying) Explain the factors affecting shelf life of fish.

6 Intrinsic factors Biological properties influence fish composition and shelf life
Larger fish spoil more slowly than small fish. Flat fish keep better than round fish Lean fish keep longer than fatty fish under aerobic storage. Bony fish are edible longer than cartilaginous fish. Flat fish with thick skin (flat fish: Halibut, skates) keeps better than thin skin (round fish: Cod) The surface/volume ratio of larger fish is lower than that of smaller fish, and, as bacteria are found on the outside, this is probably the reason for the longer shelf life of the former. This is true within a species but may not be universally so. Fatty fish are in general rejected sensorically long before lean fish. This is mainly due to the appearance of oxidative rancidity. The skin of the fatty pelagic fish is often very thin,this allows enzymes and bacteria to penetrate more quickly, and this may contribute to the faster spoilage rate.

7 Factors affecting composition of fish
Season Spawning (fat content & water) Age Young, sexually mature fish Sex Female & male Environment Feed, water temperature Body location Light & dark muscles Type of fish Sharks, Ray fish contain high urea Pelagic & demersal fish The marine environment can affect the initial microflora on the fish. For instance, a greater percentage of mesophiles and fewer psychrophiles occur in warmer waters off India, the east coast of South Africa, Australia and the Adriatic than in the colder waters off Aberdeen, Canada and the Norvegian coast. Seasonal differences in the relative proportions of various groups of bacteria have been noted by some workers. These seasonal variations are particularly evident in the gills, the area on fish being the least affected by the immediate post-catching treatments. Some species of plankton are known to exert antagonistic and antibiotic effects on bacterial populations, and these may account for lower counts recorded. Fish condition/season… hormonal variations, changes in composition, gaping…; Feeding period: digestive system is rich in bacteria and digestive enzymes that promote autolysis at post mortem stage. Despite the fact that gutting can lead to oxidation/discoloration and contamination of the flesh, it is recommended to do so as early as possible for many fish species. Ungutted cod will have a shelf life reduced of 5-6 days and the raw fillets will have a cabbagey odour.

8 Method of catching Long line Trawl net Gill net Beach seine
Quick landing Not damaging to fish Various methods of catching can be used: purse-seiner, beach-seiner, Danish seiner, trawl net, gillnet, longline are examples. The method chosen can influence the bacterial quality of the fish caught or even speed up the spoilage process if severe bruising occurs. * times heavier bacterial loads have been reported on trawled fish compared to fish caught by line. Trawling: 1. dragged along the sea bottom, collecting various bacteria 2. Fish gut contents expelled due to the pressure created while hoisting the trawl net onto the ship.

9 Post-harvest treatment
Handling on board Proper bleeding, gutting, cleaning - Rate of chilling (especially fatty fish) & temperature control GMP, hygiene, SSOP Packaging, storage & environmental conditions Unloading & auctioning Loading, transportation, retail sales & processing Handling on board such as bleeding, gutting, proper cleaning enhance the shelf life of fish. Rough handling will result in a faster spoilage rate. Storage life of many fish decrease if they have not been gutted. Temperature control methods such as cooling help to minimize the rate of spoilage. The application of Good Manufacturing Practices, standard sanitary operations and hygienic handling methods is important for post harvest practices. These practices will reduce the hazards in the industry. Packaging systems and controlled environmental conditions minimize the spoilage of fish and enhance the shelf life.

10 Time from the harvest Fish should reach the end consumer in minimum time The importance of quick landing, handling on pier and during auctioning, quick loading for transportation is emphasized to prolong shelf life. Prolonged time lower the sensory quality of fish

11 Microbiological quality of fish
Based on total count The experiment showed that the fish proceed though Beruwala harbour in mostly unacceptable (7 out of 9 situations) for human consumption. Number of unacceptable lots (out of nine) of skipjack tuna transported from Beruwala fishery harbour to Matugama & Horana. (Ganegamarachchi, et al 2002)

12 Fluctuation of core temperature in skipjack tuna handled at different time periods along the Mathugama distribution The temperature variation in fish after harvesting is shown in the graphs. Fish that was in ambient temperature takes about ½ day to cool down to 0 C. An increase in temperature is also shown in the middle stages of the 7 day stage in the sea. The temperature increase up to around 8 C within 3 hrs after unloading into pier, and further increases at fish stall. Lack of use of ice at stall cause considerable temperature increase. (Ganegamarachchi, et al 2002)

13 E. coli counts of skinned skipjack tuna in multi-day boats, at pier, in transport vehicles, at stall and at retailed stage The contamination levels of fish at different stages of distribution system is varied though out the system. Contamination occurs even in boats and continue through the pier, vehicle and stalls. The final product at retailed sales were 100 contaminated. This indicates the improper hygienic handling practices thoughout the system. (Ganegamarachchi, et al 2002)

14 Post harvest processing influences water activity and the rate of spoilage changes
Water activity aw Fresh fish aW 0.9 Dried fish aW Frozen fish aW 0.7 The figure shows how water activity in food influences the relative rate of spoilage changes i.e. lipid oxidation, non enzymic browning, water soluable nutrient losses, enzymic activity and the growth of molds, yeasts and bacteria. This is important for processed fish, like dried or frozen fish with lower water activity than fresh fish. Lipid oxidation can cause problems in frozen fish when other spoilage changes (like microbial growth) are limited because of the low temperature All microbial growth is stopped below aw 0,60. If dried fish gets moisturised then initially the moulds will develop, then the yeasts and finally bacteria. Water activity Shelf life

15 Handling on-board Quick landing Stunning, brain spiking, bleeding
Gilling & gutting Place in a chilling system for quick cooling Transfer to ice storage

16 Rate of chilling & temperature control
Rate of chilling Shelf life Variation of Shelf life with temperature 0 C 5 C 10 C shelf life RRS Crab claw 10.1 1 5.5 1.8 2.6 3.9 Salmon 11.8 8.0 1.5 3.0 Sea bream 32.0 - 4.0 Packed cod 14 .0 6.0 2.3 4.7 Calculated Table above shows an example for the shelf life with different seafood products at different temperatures The relationship between shelf life and temperature has been thoroughly studied by Australian researchers. RRS: Relative rate of spoilage H.H.Huss, 1995

17 Packaging methods for prolonging shelf life
Vacuum Packing Modified atmospheric packaging Different packing methods such as vacuum packing, modified atmosphere packaging is useful to prolong the shelf life of fish. However, it is important to emphasize that the fish used for this kind of packaging technologies should be fresh. Mechanical gas flushing and sealing with fish fillets

18 Effect of packaging on the shelf life
Type of Product Storage temp. Shelf life (weeks) Air VP MAP Meat (beef, pork, poultry) °C 1 - 3 1 - 12 3 - 21 Lean fish (cod, pollock, rockfish, trevally) °C 1 - 2 Fatty fish (herring, salmon, trout) Shellfish (crabs, scampi, scallops) ½ - 2 - ½ - 3 Warmwater fish (sheepshead, swordfish, tilapia) °C 2 - 4 vp – vacum packaging map – modified atm packaging Huss 1995

19 Effect of transportation on shelf life of fish
Proper packing & storage Use of boxes Adequate icing & cooling Hygienic conditions Clips from Video Beruwala: Packing in lories, Three wheeler transport, transport on motor cycle Kudawella: Bike transport (no ice), transport on motor cycle

20 Methods to determine shelf life
Sensory evaluation Torry or EU scheme for cooked fish, Quality Index Method (QIM) for raw/whole fish Chemical analyses Unfit for consumption when for instance TVB-N, TMA, biogenic amines have reached a certain level. Microbiological analyses Unfit for consumption when TVC > cfu/g (in fish muscle) Time and temperature history (Ref 3. Quality and quality changes in fresh fish. Chapter 6) Many methods have been proposed or tested for measuring fish quality. Sensory methods are still the most satisfactorily way of assessing the freshness of fish and are most often used to determine the shelf life. Chemical methods TMA breakdown product from bacteria, fishy ammoninical smell, low threshold, formed after a few days ice storage TVB - total volatile bases mainly ammonia and TMA measurements depend on the chosen method Hypoxanthine and K-value autolytic breakdown products from ATP mainly used on fresh water fish

21 Adapted from: Olafsdottir et al., 2006
Sensory analysis (Torry scheme) Influence of different temperature during storage (0°C, 7°C and 15°C) on the shelflife of haddock fillets The fish was processed into fillets one day after catch and stored in styrofoam boxes at different temperatures. The end of shelf-life based on Torry sensory score of 5.5 was estimated after 13.5 (12,5 +1) days from catch, for samples stored at 0 °C; after 6.5 days when stored at 7 °C and after approximately 4-5 days when stored at 15 °C Torry scheme according to Shewan et al., 1953 Shewan, J.M., Macintosh, R.G., Tucker, C.G., Ehrenberg, A.S.C., The development of a numeric scoring system for the sensory assessment of the spoilage of wet white fish stored in ice. Journal of the Science of Food and Agriculture 4, Olafsdottir G, Lauzon H, Martinsdottir E, Kristbergsson K Influence of storage temperature on microbial spoilage characteristics of haddock fillets (Melanogrammus aeglefinus) evaluated by multivariate quality prediction. Article in press Int. J Food Microbiol. August 2006 Adapted from: Olafsdottir et al., 2006

22 (Total volatile basic nitrogen) TVC (total viable counts) and
Chemical and microbial analysis Haddock fillets stored at 0°C, 7°C and 15°C TVB-N (Total volatile basic nitrogen) TVC (total viable counts) and Photobacterium phosphoreum (Pp) Chemical analysis TVB-N Based on the fixed TVB-N limit (35 mg N/100 g) as quoted in the EU regulations for gadoids (European Union, 1995) a slightly shorter shelf-life was estimated for all sample groups than when using the sensory Torry score criteria of 5.5 TVB-N is useful to detect advanced spoilage because values only begin to increase at later stages of storage It has been pointed out that TVB-N and TMA often give ambiguous information about the quality of the products as their levels are influenced by the storage method like in modified atmosphere packaging or if the fish has been pre-frozen prior to chilling Microbial counts TVC and SSO (specific spoilage organisms) Total viable psychrotrophic counts (TVC) can give controversial estimation of the end of shelf-life and different limits have been set based on product types. Shelf-life estimated by microbial growth is often shorter than when evaluated by sensory analysis. P. phosphoreum dominated the spoilage bacteria (50 to 100% of the total viable count) at all storage temperatures tested reaching levels of log 7.5 to 8.2/g at sensory rejection Adapted from: Olafsdottir et al., 2006

23 QIM-scheme for Sea bass
QIM - the principle The Quality Index Method (QIM) is based upon objective evaluation of certain attributes of raw fish (skin, eyes, gills etc) using a points scoring system (from 0 to 3). No excessive emphasis is laid on a single attribute so a sample cannot be rejected on the basis of a single criterion. Minor differences in results for any one criterion do not unduly influence the total QIM score. The lower the score the fresher the fish.

24 Changes in sensory attributes during storage
Gills have characteristic, red colour, mucus absent Eyes are clear and concave Eyes are cloudy, sunken Gills are discoloured with excessive mucus Photographs are useful to illustrate changes in appearance and colours. The figures show red fish. These figures should be replaced by original figures of tuna published in the following article K.W.S. Ariyawansa, D.N. Wijendra, S.P.S.D Senadeheera Quality Index Method developed for Frigate tuna (Auxis thasard). Sri land J. Aquat. Sci., 8:95-109 The emphasis in the methodology of sensory evaluation of fish is the harmonisation og sensory evaluation methods for fish and development of schemes for different species of fish. The QIM scheme is developed based on fish that is kept in ice throughout the storage time. More descriptions and development of schemes are needed for more species because the spoilage characteristics vary. Also, development of schemes for fish kept under different conditions (whole fish and fillets) and packaging and modified atmosphere is needed. An example of how the QIM sensory schemes can be used to predict shelflife is shown on the next slide

25 A curve to predict the storage time remaining for herring stored in ice or sea water at 0°C
There is a linear correlation between the sensory quality expressed as a demerit score and storage life on ice, which makes it possible to predict remaining storage life on ice. The theoretical demerit curve has a fixed point at (0,0) and its maximum has to be fixed as the point where the fish has been rejected by sensory evaluation of, e.g., the cooked product (see under structured scaling) or otherwise determined as the maximum keeping time. Using cooked evaluation the two parallel sensory tests demand an experienced sensory panel even though this is only required while developing the scheme, and later on it will not be necessary to assess cooked fish in order to predict the remaining shelf life. QIM does not follow the traditionally accepted S-curve pattern for deterioration of chilled fish during storage. The aim is a straight line which makes it possible to distinguish between fish at the start of the plateau phase and fish near the end of the plateau phase. When a batch of fish reaches a sum of demerit points of 10, the remaining keeping time in ice will be 5 days. To predict remaining shelf life, the theoretical curve can be converted. A fish merchant may want to know how long his purchase will remain saleable if the fish are stored on ice immediately. A buyer at a fish market might be interested in the equivalent number of days on ice where the fish have been stored since they were caught, and thus how much marketable time on ice is left. These condition indicators can be extracted for a fish sample with a known rate of change in demerit points using the quality index method.

26 References Huss, H.H. (ed) Quality and quality changes in fresh fish (chapter 6). FAO Fisheries Technical, Rome, FAO. Olafsdottir G, Lauzon H, Martinsdottir E, Kristbergsson K Influence of storage temperature on microbial spoilage characteristics of haddock fillets (Melanogrammus aeglefinus) evaluated by multivariate quality prediction. Int. J Food Microbiol.111, 112–125. E. Martinsdóttir  Quality management of stored fish in "Safety and quality issues in fish processing, Bremner, A. ed. Woodhead Publishing Ltd.. Training material from UNU-FTP/Icelandic Fisheries Laboratories Shewan, J.M., Macintosh, R.G., Tucker, C.G., Ehrenberg, A.S.C., The development of a numeric scoring system for the sensory assessment of the spoilage of wet white fish stored in ice. Journal of the Science of Food and Agriculture 4, Ganegama Arachchi, G.J. Kariyawasam, M.G.I.U., Heenatigala, P.P.M. Ariyaratne, T. Dahanayeka, T. and Jayasinghe, J.M.P.K. (2004) An investigation on the quality and handling practices of skipjack tuna (Katsuwonus pelamis) along the main commercial distribution channels of beruwala fishery harbour. Sri Lanka J. Aquat. Sci. 9: K.W.S. Ariyawansa, D.N. Wijendra, S.P.S.D Senadeheera Quality Index Method developed for Frigate tuna (Auxis thasard). Sri land J. Aquat. Sci., 8:95-109

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