Live fish muscle is relaxed and elastic. Immediately after death rigor mortis sets in, then the whole

body becomes inflexible and rigid. The onset of rigor depends upon the temperature, particularly on the

difference of temperatures between that of water and storage. If the difference is great, shorter is the time

from death to rigor. Fish being the most perishable of human foods, they start spoiling the moment they are

taken out of water and die. Temperature being a very important factor accelerating the process of spoilage,

in a tropical country like India the ambient temperatures are very conductive for causing quick spoilage in

fish. The spoilage reactions commencing on the death of the fish proceed at a very rapid pace. The rate of

spoilage of fish at 2.5°C is twice as fast as that at –1.1°C. At 5.5°C, it is twice and at 11°C it is four times

as fast as that at 0°C. The spoilage cannot be stopped completely. The best that can be done is to slow it

down by means of some refrigeration technique, the simplest of which is addition of ice

Srinivasa Gopal, T K

CMFRI Digital Repository

CMFRIWinter School onImpact of Climate Changeon Indian Marine FisheriesLecture NotesPart 1Compiled and Edited byE. Vivekanandan and J. JayasankarCentral Marine Fisheries Research Institute (CMFRI),(Indian Council of Agricultural Research)P.B. No. 1603, Cochin - 682 018, Kerala(18.01.2008 - 07.02.2008)CMFRI - Winter School on Impact of Climate Change on Indian Marine Fisheries 128Influence of temperature on the preservation of fishINFLUENCE OF TEMPERATURE ON THEPRESERVATION OF FISHT.K.Srinivasa GopalCentral Institute of Fisheries Technology,Matsyapuri P.O., Cochin-682 029IntroductionLive fish muscle is relaxed and elastic.  Immediately after death rigor mortis sets in, then the wholebody becomes inflexible and rigid.  The onset of rigor depends upon the temperature, particularly on thedifference of temperatures between that of water and storage.  If the difference is great, shorter is the timefrom death to rigor.  Fish being the most perishable of human foods, they start spoiling the moment they aretaken out of water and die.  Temperature being a very important factor accelerating the process of spoilage,in a tropical country like India the ambient temperatures are very conductive for causing quick spoilage infish.  The spoilage reactions commencing on the death of the fish proceed at a very rapid pace.  The rate ofspoilage of fish at 2.5°C is twice as fast as that at –1.1°C.  At 5.5°C, it is twice and at 11°C it is four timesas fast as that at 0°C.  The spoilage cannot be stopped completely.  The best that can be done is to slow itdown by means of some refrigeration technique, the simplest of which is addition of ice.As fish become unfit for human consumption in about 8 to 12 hours after they are taken out of water,it is imperative to cool them down with crushed ice as early as possible after they are caught in order toretain their freshness for the maximum length of time. Once the rigor is resolved, the fish become soft andbacterial proliferation starts.  Icing has to be done before this stage sets in, i.e., when the fish is stiff.Method of icing plays a very important role in bringing about cooling.  The ice should come in close contactwith the fish.  The best method of doing this is by putting ice and fish in alternative layers in the container,the bottom and top layers also being ice.  Total height of the fish-ice mixture so stored should not exceedone meter, as otherwise the fish in the lower layers gets crushed due to the weight from the above.  Thethicker the layers of fish, the more the time required to cool down. A shelf life of one hour at room temperature(say 30°C) for fresh fish is comparable to a storage life of one day in a properly iced condition.  That is tosay, a fish which retains its edibility for 10 hours at room temperature does so for 10 days when properlyiced.  Retention of edible quality of fresh fish increases with decrease in temperature.  For example a fishwhich keeps fit for human consumption for 8 to 10 hours at 30°C does so for one day at 20°C,  2 days at15°C, three days at 10°C, 4.5 days at 5°C, 10 days at 0°C, 15 to 20 days at –5°C and 30 days at –20°C.  Fishcan be stored in good condition for 3 to 15 days in ice depending on the species and several other factors.Fatty fish like sardine has a relatively shorter life of 2 to 5 days in ice.  Such fish will become easily ranciddue to oxidation of its unsaturated fat.  The belly portion becomes very soft and gets easily ruptured due tothe action of enzymes and bacteria.  It is also known that freshwater fish have longer shelf lives than marinefish in ice, so also the tropical species keeps longer in ice than cold water species.FreezingCommercial freezing involves cooling to very low temperatures such that the water in the fish isconverted into ice.  Lowering the temperature will reduce the chemical and enzymatic reactions which canlower the rate of autolysis, delay the breakdown of ATP consequently delaying the onset of rigor mortis, andalso delay the bacterial spoilage.  This forms the basis of preservation of foods by freezing.  The freezingpoint of any food will be lower than that of pure water.  Freezing begins in the fish usually at –1 to –2°c.Partial freezing or super chilling involves lowering the temperature of the fish to about –2 to –3°c.  Storagelife of the partially frozen fish is almost double that of the fish stored in ice.  However some loss of sensoryquality is experienced when the storage period extends to five days.  This is considered to be caused by thefluctuations in the storage temperature.  A change in temperature of less than 0.5°C can be instrumental inCMFRI - Winter School on Impact of Climate Change on Indian Marine Fisheries 129Influence of temperature on the preservation of fishintermittent melting or freezing of water in the fish and can have pronounced influence on protein denaturation.Dehydration or freezer burn is the most common problem encountered in fish during cold storage.  Thoughthe fish is frozen to very low temperature of even upto –40°C, the cold storage is maintained only at about–20°C to –25°C. The problem of freezer burn arises principally from a change in the relative humidity inthe cold store.  The decrease in the relative humidity increases the risk of freezer burn in the product.  Animportant defect in the cold storage atmosphere is non uniform distribution of temperature.  Circulation ofair will then cause the product to have varying temperatures at different locations leading to increaseddehydration.  Air circulation in the cold storage should be maintained at the minimum as excessive circulationcan cause increase in the incidence of dehydration.  Air, as it passes over the product, can pick up moistureand hence dehydration will be more with more air passing over it.  Similarly the design should ensure thatthe heat ingress, though it is unavoidable, is minimized.Many bacteria are killed during freezing and the survivors die off slowly. Because of the long lagperiods of bacterial growth at temperatures considerably below 0°C, the product may not undergo anyserious deterioration in quality due to microbial growth. However the frozen fish is not free from viablebacteria and other microorganisms and is therefore subject to fast spoilage when defrosted and held attemperatures suitable for their growth.  Food poisoning bacteria are known not to grow under conditions offreezing.  Enterotoxic stayphyococci do not grow below 10°C and salmonella below 5°C.  Clostridiumbotulinum types A and B do not grow and produce toxin below 10°C. However type E has been found togrow and produce toxin at temperature as low as 3°C.  Storage of frozen fish at –10°C had been consideredsatisfactory. This will arrest microbiological activity.  However the concentration of solutes in the unfrozenphase and consequent pH changes and enzyme activities can definitely accelerate some irreversible changescausing severe damage to the quality of fish.  Frozen fish stored at –20°C has almost 4 times the shelf lifecompared to that stored at –10°C.   Frozen fish stored at –30°C has almost double the shelf life than thatobtainable at –20°C.  For long time storage of frozen whole fish, fish or fish products, the ideal temperatureis –20°C to –30°C or lower.Modified atmosphere packaging (MAP)In MAP, the air in the pack of food is replaced with a mixture of gases.  Carbon dioxide, nitrogen andoxygen are the gases generally used in modifying the atmosphere. Among the different factors which influencethe shelf life and keeping quality of fish packaged under carbon dioxide enriched atmosphere, storagetemperature is one of the important factors, which influences the keeping quality of MAP products.  Theeffectiveness of MAP decreases as the storage temperature increases due to the fact that the solubility ofcarbon dioxide also decreases at higher temperatures. For respiring products, increasing the temperaturealso increases the rate of respiration, resulting in a decrease in shelf life.  The effects of temperature abuseare particularly important from the stand point of safety.  Temperature abuse of MAP muscle foods mayresult in the rapid growth of both spoilage and pathogenic bacteria.  The minimum reported temperature forSalmonella and E. coli inoculated in ground meat grew equally well at 12.5°C when the meat was packagedin low and high permeability film.  Staphylococus aureus can grow and produce enterotoxin under anaerobicconditions at 10°C or less while Yersina enterocolitica has been reported to grow at temperatures as low as–2°C.  Of major concern, with respect to safety of MAP fish is the growth and toxin production by Clostridiumbotulinum type E.  Proper refrigeration is therefore essential in order to assure the effectiveness of carbondioxide as an antimicrobial agent and to prevent potential growth of pathogenic organisms.DryingOver the years several improvements have been brought about in the process of drying keeping inview the consumer requirements.  An important achievement in drying is the development of artificialdriers where the important operational parameters like temperature, relative humidity and velocity of aircan be controlled.  This has led to dehydration which refers to a process of drying under controlled operationalparameters like temperature, air velocity and relative humidity.  Air temperature, RH of the air and airCMFRI - Winter School on Impact of Climate Change on Indian Marine Fisheries 130Influence of temperature on the preservation of fishvelocity are the parameters influencing drying rate of fish.  The difference between dry bulb and wet bulbtemperatures is related to the RH. When the difference becomes zero it implies that the air is saturated withwater vapour (RH: 100%).  A change in air temperature is usually accompanied by a change in RH.  Byincreasing the air temperature, its moisture carrying capacity can be increased; however this may adverselyaffect the quality of the product.  In the beginning of the drying cycle evaporation of water produces acooling effect on fish and air around and hence the temperature of the fish tends to fall below the ambient.Difference in temperature does not show any appreciable influence on the drying rate at this stage.  Theinfluence of temperature on drying rate becomes more pronounced in the later stages of drying when themoisture content falls.  In the low moisture range the drying rate is so slow that the cooling effect ofevaporation is not appreciable.  The fish being dried attains very nearly the temperature of the drying air.The internal distribution of water is the true factor which determines the drying rate in this phase.  This canbe accelerated by a rise in the material temperature.  The recommended temperatures for drying fish oftemperate waters is 25°C to 35°C whereas tropical fish is generally dried at 40 to 50°C.  Higher temperaturemay cause cooking of fish flesh which will make the resultant dried product brittle.  Therefore it is importantthat the temperature employed at any stage of drying is not high enough to result in cooking of fish flesh.Salt curingSalt curing, though is an important method of preservation by itself, with or without subsequentdrying, is one of the most widely practiced methods of fish preservation throughout the world.  Whenintroduced in sufficient quantities in the fish flesh, salt can delay the activity of bacteria or even inactivatethem by reducing the water activity.  This forms the basis of preservation by salting.  Temperature affectsthe salting process. With increase in temperature, salt penetration into fish flesh increases.  Increase intemperature intensifies the thermal motion of particles and also causes a reduction in the viscosity of water.But increase in temperature also may increase the rate of spoilage. If the fish is salted at lower temperatures,the rate of penetration will be reduced, but the rate of spoilage will be reduced even more.SmokingIt is an ancient method of preservation of fish.  The principle involved in this method is to expose thefish, dressed and salted in the usual manner, to smoke generated by smoldering saw dust, coconut husk etcfor various durations depending upon the degree of smoke flavour desired, followed by drying in the sun orartificially.  Smoke imparts a pleasant and agreeable flavour to the fish besides exercising preservativeaction through its several chemical constituents.  Two types of smoking, viz., cold smoking and hot smokingare popular.  Cold smoking is a mild process where temperature is not raised enough for the fish flesh toundergo even a partial cooking (below 40°C).  In hot smoking the temperature of smoke is high and the fishflesh is cooked even to the extent of partial sterlisation (above 70°C).CanningCanning is a method of preservation of food in which spoilage is averted by killing the microorganismspresent by application of heat and prevention of subsequent contamination, the product being enclosed in ahermetically sealed container.High acid foods like fish marinades and pickles containing acetic, citric or lactic acid do not supportthe growth of bacteria and hence spore forming pathogenic microorganisms will not grow in them.  Suchfoods need heat processing only at 100°C or below.  Generally the organisms that can grow in such acidicconditions can be destroyed in the temperature range 90-95°C.  Fish packaged in tomato sauce is a mediumacid food.  Such foods will require heat processing sufficient to make them safe against Clostridium botulinum.Canned fish in general, except when packed in medium like tomato sauce, is a low acid food often with pHclose to neutral.  Therefore canned fish will require heat processing as do low acid foods to ensure safetyagainst Clostridium botulinum.  All foods likely to have the presence of Clostridium botulinum are processedon the assumption that this organism is present in the food and should be eliminated.  However some heatCMFRI - Winter School on Impact of Climate Change on Indian Marine Fisheries 131Influence of temperature on the preservation of fishresistant spore forming bacteria like Bacillus stearothermophilus which are responsible for the flat sourspoilage in canned fish will survive heat processing sufficient to eliminate the spores of Clostridium botulinum.Heat treatment sufficient to ensure their complete elimination will result in over cooking of the fish.  Thereforein developing the heat processing requirements for low acid canned foods like fish, the golden rule is toavoid the contamination of the foods with such bacteria by resorting to hygienic handling practices.  Onlysafety against Clostridium botulinum is ensured in such cases.  This is the principle based on which thermalprocessing requirements of canned fish are generally arrived at.  Generally heat processing is done at 115°Cor 121°C depending on the product and medium.High Temperature Short Time processing (HTST)The relatively long time at temperatures upto 121°C employed to destroy the spoilage organisms inthe conventional heat processing may affect the quality of food in appearance, flavour and nutritive value.One of the major achievements in the efforts to overcome this problem is the development of a HighTemperature Short Time (HTST) processing technique.  The basic approach in this technique is to achievemore rapid heating of foods so that higher processing temperatures and reduced time of heating can beemployed.  For every increase of 10°C in temperature beyond the maximum conditions of growth, thereoccurs a 10 fold increase in destruction of microorganisms resulting only in doubling the rate of chemicalreactions responsible for product deterioration. Therefore, heat treatment at higher temperatures for shorterperiods of exposure results in greater retention of the natural characteristics of this product than a processof equal lethality attained by heating at a lower temperature for longer periods.  A temperature of 130-135°C is being used for HTST for thermal processing low acid products.ConclusionTemperature influences the spoilage rate and shelf life of fish in chilled, frozen, modified atmospherepackaging, drying, smoking and thermal processed products. High temperature short time processing ishaving good effect on the retention of nutrients.  Among the different methods of preservation, drying andchilling are the cheapest methods of preservation. Freezing and canning are the expensive methods ofpreservation.Suggested ReadingFraser, O.P. and S. Sumar. 1998. Compositional changes and spoilage in fish (Part II): microbiologicalinduced deterioration, Nutrition and Food Science, 6, 325-329.Gill, C.D and G. Molin. 1991. Modified atmospheres and vacuum packaging In: N. J. Russel and G. W.Gould (Ed), Food Preservatives, Blackie, Glasgow.Gopakumar, K. 2002. Fish Processing Technology. ICAR, New Delhi.Parry, R.T. 1993. Principles and application of modified atmosphere packaging of foods. Blackie Academicand Professional, U.K.Sen, D.P. (2005). Advances in Fish Processing Technology. Allied Publ. Pvt. Ltd.,  New Delhi.Srinivasa Gopal, T.K. and C. N. Ravishankar (2005). Modified Atmosphere Packaging of Fish – A Review.Fishery Technology,  42 (2), 91-110.Venugopal, V. 2006. Seafood processing: adding value through quick freezing, retortable packaging, cook-chilling and other methods. CRC press, Taylor and Francis group, USA.

Influence of temperature on the preservation of fish

 -Winter School on

Impact of Climate Change on Indian Marine Fisheries held at CMFRI, Cochin 18.1.2008 to 7.2.2008

http://eprints.cmfri.org.in/5348/1/24.pdf

Influence of temperature on the preservation of fish -Winter School on Impact of Climate Change on Indian Marine Fisheries held at CMFRI, Cochin 18.1.2008 to 7.2.2008

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