Presentation on theme: "Factors influencing storage & shelf life of fresh fish"— Presentation transcript:
1 Factors influencing storage & shelf life of fresh fish Quality and safety issues in fish handling-----A course in quality and safety management infishery harbours in Sri LankaNARA, DFAR, ICEIDA and UNU-FTPLearning objectivesAfter this lecture participants will be:- familiar with shelflife and factors affecting shelflife of fish raw materials.Icelandic International Development Agency (ICEIDA)IcelandUnited Nations University Fisheries Training Programme (UNU-FTP)National Aquatic Resources Research and Development Agency (NARA)Sri LankaDepartment of Fisheries and Aquatic Resources (DFAR)
2 Factors affecting shelf life How to determine shelf life ContentWhat is shelf lifeFactors affecting shelf lifeHow to determine shelf lifeThe content of the lecture is about the shelf life, factors affecting shelf life and the methods to determine the shelf life.
3 Learning ObjectivesAfter 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 lifeShelf life can be defined as the period of time that the fish is fit for consumptionThe limit of shelf life i.e. when the fish becomes unfit for consumption can be determined based on sensory, chemical or microbial criteriaTime and temperature of storage can also be used as criteria to determine the limit of shelf lifeQuality parameter rather than a safety parameterStrongly 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 speciesCommercial 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 CompositionMethod of catchingPost harvest treatmentProcessing (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 fishLean 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 SeasonSpawning (fat content & water)AgeYoung, sexually mature fishSexFemale & maleEnvironmentFeed, water temperatureBody locationLight & dark musclesType of fishSharks, Ray fish contain high ureaPelagic & demersal fishThe 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 landingNot damaging to fishVarious 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 bacteria2. Fish gut contents expelled due to the pressure created while hoisting the trawl net onto the ship.
9 Post-harvest treatment Handling on boardProper bleeding, gutting, cleaning- Rate of chilling (especially fatty fish) & temperature controlGMP, hygiene, SSOPPackaging, storage & environmental conditionsUnloading & auctioningLoading, transportation, retail sales & processingHandling 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 harvestFish should reach the end consumer in minimum timeThe 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 countThe 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 distributionThe 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 stageThe 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 awFresh fish aW 0.9Dried fish aWFrozen fish aW 0.7The 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 temperatureAll 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 & guttingPlace in a chilling system for quick coolingTransfer to ice storage
16 Rate of chilling & temperature control Rate of chilling Shelf lifeVariation of Shelf life with temperature0 C5 C10 Cshelf lifeRRSCrab claw10.115.51.82.63.9Salmon11.88.01.53.0Sea bream32.0-4.0Packed cod14 .06.02.34.7CalculatedTable above shows an example for the shelf life with different seafood products at different temperaturesThe relationship between shelf life and temperature has been thoroughly studied by Australian researchers.RRS: Relative rate of spoilageH.H.Huss, 1995
17 Packaging methods for prolonging shelf life Vacuum PackingModified atmospheric packagingDifferent 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 ProductStorage temp.Shelf life (weeks)AirVPMAPMeat (beef, pork, poultry)°C1 - 31 - 123 - 21Lean fish (cod, pollock, rockfish, trevally)°C1 - 2Fatty fish (herring, salmon, trout)Shellfish (crabs, scampi, scallops)½ - 2-½ - 3Warmwater fish (sheepshead, swordfish, tilapia)°C2 - 4vp – vacum packagingmap – modified atm packagingHuss 1995
19 Effect of transportation on shelf life of fish Proper packing & storageUse of boxesAdequate icing & coolingHygienic conditionsClips from VideoBeruwala: Packing in lories, Three wheeler transport, transport on motor cycleKudawella: Bike transport (no ice), transport on motor cycle
20 Methods to determine shelf life Sensory evaluationTorry or EU scheme for cooked fish, Quality Index Method (QIM) for raw/whole fishChemical analysesUnfit for consumption when for instance TVB-N, TMA, biogenic amines have reached a certain level.Microbiological analysesUnfit 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 methodsTMA breakdown product from bacteria, fishy ammoninical smell, low threshold, formed after a few days ice storageTVB - total volatile basesmainly ammonia and TMAmeasurements depend on the chosen methodHypoxanthine and K-valueautolytic breakdown products from ATPmainly 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 filletsThe 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 °CTorry scheme according to Shewan et al., 1953Shewan, 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 2006Adapted 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°CTVB-N(Total volatile basic nitrogen)TVC (total viable counts) andPhotobacterium phosphoreum (Pp)Chemical analysis TVB-NBased 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 5.5TVB-N is useful to detect advanced spoilage because values only begin to increase at later stages of storageIt 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 chillingMicrobial 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 rejectionAdapted from: Olafsdottir et al., 2006
23 QIM-scheme for Sea bass QIM - the principleThe 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 absentEyes are clear and concaveEyes are cloudy, sunkenGills are discoloured with excessive mucusPhotographs 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 articleK.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., 8:95-109The 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 ReferencesHuss, H.H. (ed) Quality and quality changes in fresh fish (chapter6). FAO Fisheries Technical, Rome, FAO.Olafsdottir G, Lauzon H, Martinsdottir E, Kristbergsson K Influenceof storage temperature on microbial spoilage characteristics of haddockfillets (Melanogrammus aeglefinus) evaluated by multivariate qualityprediction. Int. J Food Microbiol.111, 112–125.E. Martinsdóttir Quality management of stored fish in "Safety andquality issues in fish processing, Bremner, A. ed. Woodhead Publishing Ltd..Training material from UNU-FTP/Icelandic Fisheries LaboratoriesShewan, J.M., Macintosh, R.G., Tucker, C.G., Ehrenberg, A.S.C., Thedevelopment of a numeric scoring system for the sensory assessment of thespoilage of wet white fish stored in ice. Journal of the Science of Food andAgriculture 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) Aninvestigation on the quality and handling practices of skipjack tuna(Katsuwonus pelamis) along the main commercial distribution channels ofberuwala fishery harbour. Sri Lanka J. Aquat. Sci. 9:K.W.S. Ariyawansa, D.N. Wijendra, S.P.S.D Senadeheera Quality IndexMethod developed for Frigate tuna (Auxis thasard). Sri land J. Aquat. Sci.,8:95-109