Intrinsic & Extrinsic parameters controlling Fish Spoilage Dr. Subhendu Datta Sr. Scientist CIFE, Kolkata Centre, India

Extrinsic parameters Temperature of storage Relative humidity Oxygen concentration Salinity Exhaustion of fish before catch Load of external microorganisms in the fish body By controlling these parameters it is possible to control spoilage.

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Storage Temperature Higher the temperature quicker the dissolution of rigor and onset of autolysis and bacterial decomposition. Each bacterial species has a range of temperature in which it has optimum growth. Also there is a minimum temperature below which the growth does not take place and a maximum temperature above which bacteria cannot grow. Cold loving bacteria – Psychrophilic (0(0-200C). Opt 150C e.g. e Psuedomonas Mesophilic bacteria – 2020-450C, Opt. 30 - 370C, e.g. Salmonella typhi. Thermophilic bacteria – 4545-700C, Opt 550C, e.g. Clostridium botulinum.

Temp… Therefore, most of the spoilage bacteria grow faster with the rise in temperature, thereby produce unpleasant endendproducts. Therefore, the practical way to preserve fish in good condition is to store the fish at low temperature. After landing, fish should be immediately cooled down to the temperature of melting ice to retard quality loss. Chilling, however, only slows down the microbial activity, since psychrophilic bacteria are able to survive in chilled fish.

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Temp…. "Gaping" depends on temperature; the higher the temperature of fish at the beginning of the rigor mortis process the greater the gaping of the muscle. Gaping is muscle separation in fish fillets (during storage) which is considered a quality defect. Therefore, during rigor mortis fish temperature should be as low as possible.

Temp… Fish body temperature is a decisive factor in the onset and duration of the rigor mortis process. The higher the temperature the sooner it begins and the faster it ceases. For example, for roach and perch kept at 0° 0°C, rigor mortis begins 24 hours after death and lasts for 7272-80 hours. When the same species is kept at 35° 35°C, it begins 2020-30 minutes after death and stops after about 3 hours.

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Temp.. This is evidenced by enzymatic reactions whose speed increases with increased temperature. At high temperatures it results in greater changes in proteins, the latter causing higher loss of tissue juices during processing. Usually, the later rigor mortis begins and the longer it lasts, the longer are the storage life of the fish and its use for consumption.

Temp… Chilling and freezing is an effective way of reducing spoilage in fish, if it is done quickly, handled carefully and hygienically. Higher the temperature of storage, shorter the shelf life of fish. As a general rule, for every hour that the fish are kept at ambient temperature the equivalent of one day's storage life is lost and for every 50C and 00C that they are stored, the storage life in ice is reduced by half.

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Temp… Freezing is by far the best method of heat removal of fish. The faster the freezing process, the lesser the spoilage. Therefore, quick freezing is adopted commercially. The recommended level at which the temperature of the fish has to be brought down is -300C and the interior part of the fish has to be -200C.

R.H. Higher the R.H. higher the chances of spoilage by bacteria. Small fishes can be salted and dried within 2 days, but during inclement weather when the R.H. is high the period could extend to 55-7 days. This results in poor quality of fish due to harbouring of spoilage bacteria and insect larvae.

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Fish Catching Technique or Exhaustion of fish before catch The concentration of lactic acid formed due breakdown of glucose is found to be dependent on the glycogen reserves of the muscle prior to death. death. The glycogen reserve of the muscle is directly related to the struggle struggle the fish has undergone prior to capture and death. The greater the struggle the fish has experienced the lesser are its glycogen reserves and the onset of rigor mortis becomes rapid.

Therefore, Rigor mortis proceeds very quickly in very active fish but rather slowly in inert fish. One consequence of the accumulation of lactic acid in the muscle is the lowering of pH from near neutrality (pH 7.0) to the lactic acid range (pH 6.0). The decline of pH affects the quality of the fish tissues, in that that flesh become firmer and tendency to drip enhances. But after the death of fish fish acidic pH is better than alkaline pH to prevent microbial decomposition.

Fish Catching Technique/handling…. In those fish which are in good condition (well(well-nourished) rigor mortis is more intensive. Fish put to death just after removal from the water reach a state of rigor mortis later than those fish which died after a long agony. In the case of carp put to death just after capture rigor mortis begins after 48 hours, but if the carp died after a long agony it sets in after 24 hours (at 0° 0° C).

Unnecessary and rough handling of the fish can shorten the time of occurrence and duration of rigor mortis. mortis. Such treatment causes stress in live fish.

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handling Efficient handling immediately after shrimp harvest is very effective in preventing black discolouration on raw shrimp. Tyrosinase and polyphenol oxidase, that catalyse black spot formation, are present in large quantities in the digestive system of the shrimp.

Oxygen concentration Oxidative rancidity - Oxidation of fish oils yielding the rancid odours and tastes which are the major problem encountered in fish storage. Lowering of oxygen level reduce the magnitude of rancidity Aerobic - Bacteria which grow only in the presence of air. e.g. Micrococcus. Anaerobic - Bacteria which grow only in the absence of oxygen. e.g. Clostridium sp. Facultative – Bacteria grow in presence or absence of oxygen. Ex. Salmonella, Vibrio Microaerophilic – bacteria grow better in the presence of very little free oxygen. Ex. – Lactobacillus, Streptococcus

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Salinity Halophilic - Bacteria which grow best in the presence of salt. e.g. Serratea salinaria. Halophobic - Bacteria which cannot tolerate salt concentrations higher than 6%. e.g. Achromobacter, Pseudomonas. The population and nature of bacterial flora depend on the waters from where the fish are caught i.e. whether from sea water, brackish water or fresh water.

Depending on the salinity and pollution range of waters, the bacterial flora of fishes vary from water to water. Majority of bacterial flora of marine fishes are gram negetaive, negetaive, nonnon-spore forming rods or cocci. cocci. Bacterial flora fresh water fishes are predominantly gram positive in nature. There are large number of bacterial types in marine water than Fresh water

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Load of external microorganisms in the fish body Fish often get contaminated through woodenwooden-boxes, ice, dressingdressing-tables etc., which usually carry heavy bacterial load. Proper treatment of surfaces, equipments etc., with disinfectants disinfectants and detergents, and use of potable water for washing and iceice-making are necessary to reduce bacterial contamination. The initial bacterial load and the nature of contaminants play a vital role in the deterioration of fish in the later stages. Slime contains large amounts of nitrogenous compounds and these provide good nourishment for micromicro-organisms originating from the environment. Fish which secrets more slime, contains more microorganisms from the environment After bringing to the factory, the fish are washed with flowing water to remove the heavily contaminated slime.

Intrinsic parameters Intrinsic quality means the sum of attributes that

are inherent in the harvested raw material (Connel, Connel, 1980).

It is somehow more difficult to control the

inherent properties of fish tissues that influence enzymatic and microbial spoilage of fish.

The intrinsic moisture content, pH, physical and

chemical nature of fish (fresh or marine), in part, control the number and types of microorganisms involved in the spoilage process.

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In the case of fish, caught in the wild, the complete control or manipulation of intrinsic quality is impossible. But two types of control are possible. The first is conscious selection of grounds, seasons or fishing methods. The second is selection or sorting from mixed catches, the fish of desired quality. In the case of cultivated fish active control of intrinsic quality is feasible.

Factors affect the intrinsic quality The factors that affect intrinsic quality are Species Size Sex Condition and composition Parasites and other organisms Naturally toxic fish Contamination with pollutants

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Species Certain fishes are generally costly as they are rated as “good fish” fish”. Ex. – Rohu & Catla fetches more price than Mrigal, Mrigal, Silver carp, common carp, Tilapia Marine fishes contains more lipid than freshwater fishes. Therefore, chances of rancidity is higher in marine fishes than freshwater fishes.

Species… The time rigor mortis begins and its duration depend on the fish species. species. For carp at 0° 0°C, it starts after 48 hours, For roach and perch at 0° 0°C after 24 hours It was also found that fast swimmers, for example trout, undergo rigor mortis faster but for a shorter duration than slow swimmers like carp. carp.

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Species… Fish which secrete great quantities of slime have poorly developed scales; very often the quantity of slime reaches 22-3% of the fish mass and that in turn creates problems during processing. Slime contains large amounts of nitrogenous compounds and these provide good nourishment for micromicroorganisms originating from the environment. Therefore, the slime spoils quickly: first giving an unpleasant smell to the fish, and second opening the way for further and deeper bacterial penetration into the fish.

Species… During storage Non-fatty (or white fish) keep longer than fatty fish. Freshwater fish keep longer than marine fish Fish from warm waters keep longer than fish from temperate waters.

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Size In general, large fish of a given species fetch the higher price, for example, shrimp, Scampi, crab, lobster. The % yield of edible material is higher and handling cost per unit weight is lower in large fish of a given species.

It is a fact that large fish keep better than small fish. This can be attributed to: The smaller surface area to volume ratio for large fish so that in the same time period, less of the interior of large fish is affected by spoilage micromicro-organisms penetrated from the surface to the interior. Small fish of a given species tend to have a higher postpost-rigor pH than large fish of the same species, thus giving rise to the greater bacterial action.

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Sex In certain species, the females are of very poor quality soon after spawning. The canned product made from female Capelin (Malloters villosus) is very different from that made from male capelin.

Condition & Composition During certain period fish appear thinner, flabbier and less lively, the flesh being more watery and softer and containing less protein and fat. The fat content of many species vary considerably throughout the year. After spawning the fat content of many fishes vary considerably.

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Parasites, bacteria Sea fishes can harbour protozoa and intestinal worms which are dangerous Intrinsic bacteria and viruses in the slime, gill, guts and intestine of the fish Bacterial population in fish body: Skin surface < gill tissue < Intestine Summer months > winter months

Naturally Toxic fish Due to Ciguatera toxicity in the flesh of fish & shellfish inhabiting shallow waters in or near subtropical coral reefs. Paralytic shellfish poisoning in molluscs & calms during the period of in the high concentration of dinoflagellates in sea. These poisoning spoil the fishes in source.

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Contamination with pollutants

Metals (Hg), chlorinated hydrocarbons, Mineral oils, radioactive isotopes, antibiotic residues etc. contaminate the fishes in source and are therefore, intrinsic in nature.

Moisture content of fish body Higher the moisture content higher will be the spoilage. Bacteria need water for growth and multiplication. Below a minimum level of water activity (aw), microorganisms cannot grow. When we dry fish, water is removed from the fish muscle to a level below 0.9, so that bacterial action is completely prevented. By drying & salting, the moisture content of fish is brought around 38% when bacterial growth is inhibited. When the moisture content of fish is reduced to 25%, autolytic activity is greatly reduced, while mould growth is prevented if moisture level is reduced to 15%.

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pH Lower the pH lower the decomposition by bacteria. Acidophiles - Bacteria which can survive at a pH of 4.5 and below. e. g. Lactic acid bacteria. Example: Fish silage is preserved against the microbial spoilage mainly by the lowered pH, obtained by the added or in-situ produced acid. Specifically, the unionized acid molecules are able to cross the cytoplasmic membrane barrier of the microbial cell while protons (H+) and acid anions cannot.

pH… But once inside the bacterial cell, the acid molecule can ionize, and since the membrane traps the ions, the pH gradually comes down killing the cell. Thus, it is the unionized acid molecules that are responsible for the preservative action rather than the total acid concentration. At equal concentrations, organic acids are weekly ionized in solution compared to inorganic acids, thus contain greater amounts of unionized (free) acid molecules making them more effective preservatives.

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pH…. Once the rigor mortis ceases, bacterial spoilage becomes rapid. This is accompanied by the rise of muscle pH from acidic range to alkaline range (sometimes upto pH 8) due to accumulation of volatile bases like ammonia and trimethyl amine (TMA) produced by spoilage of fish.

pH… Spoilage bacteria present is the fish tend to minimize the rich free amino acid pool present as energy source and produce ammonia thereby increase the pH (by deamination reaction caused denaturation of protein). Number of lactic acid bacteria (LAB) present in fish are too few to result in their dominance over much greater number of spoilage microflora. microflora. Because of this reason, sugar and innoculum of lactic acid bacteria is added in fish silage to provide a head start to lactic acid fermentation.

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Physical and chemical nature of fish (fresh or marine) Already discussed before under the title “Species”.

Summary So to reduce the spoilage of fish during storage; Reduce the temperature of storage (< - 200C) Reduce the moisture content of the fish (<20%) Reduce the pH (< 7) of stored fish Reduce the rough handling of fish during catching, packing, storing etc. Reduce R.H., O2 during storage Reduce storing of smaller sized fish Reduce the time lag between catching of fish and preservation

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