Radiation Technique to Improve the Quality of Fishery Products in Fish Processing Technology
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Radiation Technique to Improve the Quality of Fishery Products in Fish Processing Technology


Jaya Naik1, C.V. Raju2, N. Rajendra Naik3 and Naresh, K. Mehta4

      1Research Scholar (UGC), 2Assistant Professor and 3 and 4Post Graduate Students

Dept. of Fish Processing technology, College of Fisheries, Mangalore


Radiation Processing

Food irradiation is a process for the treatment of food precuts to enhance their shelf life and to improve microbial safety. The chemistry, technology and commercial aspects of food irradiation have been discussed in a number of articles and books over the years. Magnetic radiations, namely gamma and X-rays having short wave length (<300 nm) and higher energy than visible light, can cause ionization by removing electrons from the outer cell of atoms and molecules. Generally, ionizing radiation emitted by radioisotopes, Cobalt 60, and Cesium-137 are used for food preservation. Cobalt-60 isotopes (half life, 5.3 years) emit 2 gamma rays of 1.17 and 1.33 million electron volts (MeV), whereas Cesium-137 (half life, 30.2 years) emits a gamma ray of 0.66 MeV.Cobalt-60 is made by neutron bombardment of Co-59, which stabilizes by emitting radiations and forming non-radioactive nickel.

 From the practical point of view, Co-60 is preferable to Cesium-137 because the later apart from having weaker gamma rays are also water soluble, thus posing environment hazard. Most of the present day irradiations use Covbalt-60 as a source of radiation energy on accounts of its high penetration and easy availability. Some of the public concerns associated with transportation, installation and operations of permanent radiating sources such as Co-60 may lead to increasing use of electrons and X-rays. Both electrons and X-rays being machine generated can be turned off and on. Food irradiation electrons beams at energy levels up to 10 MeV and X-rays at a energy levels up to 5 MeV are permitted. Although electrons are less penetrating than gamma rays, they can be very useful for irradiating large volumes of free flowing food items, such as grains, or packages of foods such as fish fillets not more than 8-10 cm thickness with density of 1 gcm3. X-rays have maximum energy of 5 MeV and similar penetrating power as gamma rays. Despite good penetration power and dose rate, X-rays are not used in food irradiation due to poor conversion of accelerated electrons to X-rays. The effects of gamma rays and electron beams are however comparable.

Absorbed dose and dose rate

The quantity of energy absorbed by the food during irradiation is called absorbed dose. The unit for irradiation dose is the Gray (Gy), which is equal to the absorption of energy equivalent to 1 J/kg of absorbing material (1 Gy = 1 joule. kG-1 = 100 rad). The dose rate of gamma rays from commercial Co-60 sources is 1-100 Gy/minute, while those of electron beams from accelerators are 103 to 106 Gy/sec. When an electron beams penetrates an aqueous medium, the dose some what below the surface is higher than at the surface.

Conditions for irradiation

            Food irradiation is essentially a cold process because that treatment does not cause any significant raising temperature. However, temperature of the product being irradiated as an influence on the radiation induced changes. Movement of free radicals increased with the temperature, affecting the over all rate of radiolysis lower temperature reduces the production of volatiles in food products, which known to affect the sensory quality of irradiated foods such changes are at a minimum in frozen products.


Effect of irradiation on fish muscle component  

Proteins and amino acids: Extensive data on radiation chemistry of amino acids, proteins and other food components are available. In vitro studies have shown that free amino acids and amino acids of proteins are sensitive to radiations. Free radicals formed by radiolysis of water, namely hydroxyl, hydrogen, aqueous electron react with amino acids leading to abstraction of hydrogen and reductive deamination. The radicals produced will react further, for ex by disproportionate. These reactions are followed by decarboxylation and deamination giving rise to ammonia and pyruvic acid, for ex, in case of alanine. In the presence of oxygen oxidative deamination replaces reductive deamination. Cystine, cysteine, and methionine act as scavengers and react more readily with free radicals than the non sulphur containing aliphatic amino acids. The aromatic amino acids phenylalanine and tyrosine react readily with the transient species of water radiolysis, hydroxylation of the aromatic ring being the principle reaction. Phenylalanine hydroxylation to form tyrosine isomers. Hydroxylation converts these two dihydroxy phenyl alanine (DOPA) catalyzed by the phenyl oxidase. Subsequent oxidation of DOPA and polymerization can produce melanin type pigment (black spot), as observed in the case of shrimp.  


  Irradiation may influence the textural attributes of fish muscle. The treatment at 5 kg enhanced the drip formation to level as high as 20% in Bombay duck, which could be reduced to 7-8% by pre-irradiation dipping in 10% solution of either sodium tri polyphosphate or sodium chloride. Treatment at dose of 0.66 or 1.31 kGy caused decreased in gel strength of mince red hake (Urophysis chuss) The degree of textural changes in precooked lobster by irradiation at 1 kGy were comparable to that developed of storage for 3-4 months. Irradiation at 1.5 kGy did not affect the disperseability and viscosity characteristics of textural proteins of India mackerel.

Radiation process for fishery products

Radurization: is the irradiation process for extension of shelf life of fresh fishery products in ice or under refrigeration by reducing the number of spoilage causing bacteria. Two factors are most significant in determining the optimum radiation dose for radurization. These arise from qualitative and quantitative changes in the microbial growth and radiation dose responses of tissues constituents that govern the organoleptic attributes of fishery products. Radiation sensitive gram negative bacteria are mostly responsible for spoilage of fishery products. Therefore the reduction of spoilage causing microorganisms by low level of radiation leads to an extension of shelf life of fishery products. Radurization is done in the dose range of 1-3 kGy, which is sufficient reduce the initial load of spoilage causing organisms by about 1-3 log cycles. The optimum dose is selected to give a product with e\extended shelf life in ice, having a terminal spoilage pattern that should not considerably different from that of un irradiated samples. The treated product has a shelf life of 2-3 times that of unpredicted counter part. The treatment is effective for extension of shelf life of most marine and fresh water species. Initial quality of fish is important in obtaining maximum extension in shelf life, ideally fish iced immediately after catch should be irradiated for maximum extension of shelf life. However, the fish stored in ice for 2-3 days after catch can also be treated. A longer delay can adversely affect influence of post irradiation shelf life. Thus fillets from low quality haddock after irradiation were found to be border line in quality for most of their extended storage life. 


 Radicidation denotes sanitization of frozen products by the elimination of pathogenic microorganisms by irradiation. In recommending the treatment dose ranges necessary to reduce or eliminate food borne pathogens in foods, it is important to consider the nature of the product, handling conditions, its intended use, and other technological conditions of processing. Mossell observed that irradiation at a dose of 2 kGy was adequate significantly eliminate different pathogens, including Shigella sp and Staphalococcus aureus from frozen shrimp. A dose of 4 kGy has been found to be adequate enough for elimination of non spore forming pathogens in different kinds of frozen foods, including seafood.

Combinations of process involving irradiation   

The preservative effects of ionizing radiation can often be combining advantageously with effect of other physical and chemical agents. The resulting combination treatments may involve synergistic or cumulative action of the combination partners leading to a decreased treatment requirement for one or both the agents. This in turn may result in savings in both cost and energy and may bring about an improvement in the sensory properties and bacteriological quality of the food thus treated. Preservative effects of combinations of treatments in controlling microbial growth and resulting spoilage is based on hurdle technology and involves the creation of series of hurdles in the foods for microbial growth. Such hurdles include heat, irradiation, low temperature, water activity, and pH, redox potential and chemical preservatives.


Radappertization or radiation sterilization is analogues to thermal canning is achieving shelf stability of processed products requires ambient temperatures. The treatment requires exposing food in sealed containers to ionizing radiation at dose ranging form 25-70 kGy to kill all organisms to provide commercial sterility to the products. Because autolytic enzymes cannot be inactivated by irradiation even at these high-dose levels, it is essential that the food items are subjected to a heat treatment at 700 to 800 C to inactivate the enzymes. To minimize the occurrence of oxidative changes leading to off flavors, undesirable color changes, as well as textural and nutritional losses, the food is vacuum packed either in metal cans or flexible pouches, frozen at -400C and irradiated in the frozen condition at -200C to -400C.


Irradiation can effectively reduced or eliminate pathogens of public health significance, spoilage causing microorganisms, insects and parasites. The major benefit of the application of fishery products of is in the reduction of post harvest losses and the Improvement of the hygienic quality of fishery products. Irradiation at appropriate doses and conditions can augments sanitation measures and good manufacturing practices to provide safe and wholesome products. These in turn, can results in expansion of the fresh sea foods, market, and stabilization of the supply, greater use of the resources and stabilization of fish quality. The treatment can ultimately result in an increased consumer confidence in the products resulting from the improved hygiene, increased overall sales and marketing.



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