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 Ð 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.
Texture
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
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
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.
CONCLUSION
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.
