Food Microbiology

Food Preservation by Irradiation

Food radiation (the process of applying ionizing radiations to food items) is a technique that enhances the safety and prolongs the shelf-life...

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This article writter by MN Editors on August 02, 2022

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Food Preservation by Irradiation
Food Preservation by Irradiation

Food radiation (the process of applying ionizing radiations to food items) is a technique that enhances the safety and prolongs the shelf-life of food by eliminating or reducing pests and microorganisms. As with pasteurizing milk, and making preserves for vegetables and fruits radiation could make food safer for consumers.

  • Foods are not made radioactive, alter nutritional quality, or alter the flavor, texture or appearance of food items. The changes caused by radiation are so minor that it’s hard to discern if a food item has been radioactively treated.
  • Food is typically exposed to radiations that ionize for eliminating microorganisms and bacteria, insects or viruses may be present in the food.
  • Other applications include delay of maturing, increasing juice yield, inhibition of sprouts and better the rate of rehydration.
  • In some cases the irradiation of food can cause massive chemical changes.
  • The effects of radiation are not just on food items, but also on non-food items including medical equipment plastics, plastics, tubes for gas pipelines, homes for floors, floor heaters, shrink-foils to heat floors, food packaging, car parts, cables and wires (isolation) and tires and even gems.
  • Food irradiation has great potential as a novel method for increasing standards for food safety and quality through the destruction of harmful microorganisms, such as E. Coli.
  • The process of irradiation also aids in the reduction of spoilage-related bugs, parasites and bacteria. It’s gained importance as a top quality food hygiene procedure through the elimination and reduction of harmful microorganisms as well as bacterial populations.
  • The Food and Drug Administration has granted approval to irradiation as an effective method of preserving food quality and extending the shelf longevity of meat, fresh fruits, vegetables and spices.
  • Irradiation processes are also utilized in certain vegetables and fruits to delay and stop maturing and sprouting processes.

Purpose of Irradiation 

  • Prevention of Foodborne Illness – Effectively eliminate the organisms that can cause foodborne illnesses, like Salmonella as well as Escherichia coli (E. coli).
  • Preservation – to eliminate or kill organisms that contribute to spoilage and decomposition , and to extend the shelf-life of food items.
  • Control of Insects – to eliminate insects that are found on tropical fruits that are imported to the United States. It also lessens the need for other pest control methods that could cause harm to the fruit.
  • Delay of Sprouting and Ripening – in order to stop sprouting (e.g. potatoes) and also delay the ripening process of the fruit in order to prolong its life.
  • Sterilization – Irradiations are employed to sterilize food items that can be stored for years with no refrigeration. Foods that have been sterilized can be useful in hospitals for patients suffering from severe impairments to their immune systems, like those with AIDS or who are undergoing chemotherapy. Foods that have been sterilized with radiation are exposed to significantly more treatment levels than those that are approved for use in general.

Effects of Irradiation

  • The effects of radiation cause destruction and permanent DNA damage in pathogenic organisms. In the process, they lose the ability to expand and multiply.
  • If there are insects in food products, they are sterile and incapable of reproduction, and plants stop their natural ripening process.
  • The process of irradiation of food is referred to as “cold pasteurization.”. Energy density for each atomic transition in the ionizing radiation is extremely high.
  • It can break into molecules and causing the process of ionization. This is not accomplished by heating.
  • Ionizing radiations produce the same effects as pasteurization with heat of liquids like milk.
  • Irradiation of food is considered to be preservation through cold since this type of treatment doesn’t cause an increase in temperature that is significant.
  • The temperature of food products that have been irradiated influences physical changes that result from the exposure of radiation. Temperature increases cause an the formation of free radicals that migrate that affect the speed of the radiolytic process.
  • The lower temperature reduces that production of volatile compounds within food items. These volatiles have been proven to alter the sensory quality of food products that have been exposed to radiation. The opposite is that refrigeration produces a low level of these modifications

Sources of Irradiation 

The three radiation sources are which are approved to be used on food items.

  • Gamma radiation is emitted by radiation-producing forms of cobalt (Cobalt 60) or from ceasium (Cesium Cesium). Gamma radiation is commonly used to sterilize dental, medical products, household items and is also utilized for treatment of cancer with radiation.
  • X-rays are created by reflecting an electron stream with high energy off the target substance (usually some of the heavier metals) to produce food. The X-rays are also extensively utilized in the fields of medicine and industry to create pictures of the internal structure.
  • The electron beam (or e-beam) is like X-rays in that it is a high-energy stream of electrons that is accelerated from an electron accelerator to food.

Types of Irradiation in Food Preservation

There are various kinds of irradiation processes that are employed for the preservation of food like;

  1. Non-ionizing  Irradiation
    1. Ultraviolet Irradiation
    2. Microwave
  2. Ionizing Radiation
    1. X-ray
    2. Gamma rays
    3. Beta Rays
    4. Cathods ray
Food Preservation by Irradiation
Food Preservation by Irradiation

1. Non-ionizing  Irradiation

  • Nonionizing radiation refers to any kind or electromagnetic signal that doesn’t provide sufficient energy to effectively ionize the atoms or molecules, which means that it the electron cannot be removed from an atom or molecular.
  • While they do not produce charged ions while passing through the material, nonionizing radiations are able to produce enough energy for excitation only and the transition of an electron to a higher energy level.
  • Sound waves, ultraviolet lights visible and infrared light radio waves, microwaves as well as radio frequencies are just a few examples of nonionizing radiation.
  • The radiation that comes from the Sun that is reflected to the Earth is mostly composed of nonionizing radiation. However, the majority of it is blocked from the atmosphere of the Earth.
  • Nonionizing radiation poses a significant danger to the health of individuals if not appropriately managed.
  • If nonionizing radiations are employed during food preparation, the hazard symbol should be displayed on the front of the room for processing.

A. Microwave Processing

  • Processing and heating of microwaves for food items is becoming more popular, especially at the level of the consumer.
  • The microwave spectrum within the spectrum electromagnetic is comprised of frequencies between 1012 and 109 Hz and has a low amount of energy.
  • Two frequencies are employed for food processing 2 frequencies are used: 2450 and 915MHz.
  • Microwaves affect microorganisms indirectly by generating heat. When food items that are electrically neutral are put in an electromagnetic field of microwaves, these charged and asymmetric molecules get formed.
  • In this process, every asymmetric molecule tries to match itself to the shifting alternating current field.
  • When molecules move around on their axes, trying to reach the correct poles of negative and positive, intermolecular friction develops which produces heat.
  • Microwaves can be used to aid in eliminating mold found in beer, bread, wines along with potato chips.
  • Microwaves are a great way to eliminate yeast and mold on meat prior to use in hamburgers, fruits and vegetables. They can also be used to blanch and soft bakery items and dry pasta to pasteurize.
  • Foods are packed in advance of the microwave radiation. Heating with microwaves may cut down processing times, energyuse, and water use in certain areas of food processing.
  • Microwaves can be used to heat food items or to eliminate food-borne pests.
  • Microwave heating is a useful tool for cooking at home.
  • The development of different temperatures in a food can result in problems like inadequate heating of certain portions of food, making it possible for pathogenic microorganisms to survive.
  • The food’s geometry as well as its thermal resistance the dielectric and physical properties of it, its weight and power input and the frequency of radiation influence the interactions of electromagnetic waves and food. These elements can result in the different types of microwaves to heat ingredients in food.
  • This thermal irregularity hinders the use of microwave heating in process of microbial activation.

B. Ultraviolet Irradiation

  • Low-pressure mercury Vapor discharge lamps are employed to produce the ultraviolet (UV) light. 80 percent of UV radiation is located at 254 nm.
  • The wavelength below 200 nanometers is absorption by oxygen in air, generating ozone which can be harmful to living matter. Light output drops off with time, and they must be checked regularly.
  • UV light is a potent antibacterial agent with a wavelength of 240 to 280 nm.
  • The high microbiological effectiveness in UV results from its destruction of nucleic acids.
  • The cross-linking between thymine dimers within DNA blocks reproduction and repair that could cause the inactivation of microorganisms.
  • The energy generated by UV radiation stimulates electrons within molecules away from their initial state to orbitals with higher energy, which makes the molecules more reactive.
  • The electromagnetic fields trigger the cell’s membranes to shift ions and alters in permeability. This causes functional disturbances, breaking up of cell structures, as well as the failure of crucial metabolic processes. These changes cause cells dying or injury.
  • The most lethal effect is seen in the wavelength of 260-nm. This is due to an intense absorption of radiation through nucleic acid bases as well as proteins, which can cause changes in photochemistry and the death of cells.
  • The passage through 5 cm of clear water can reduce radiation intensity UV radiation to two-thirds and 90% of radiation is absorbed through a layer of milk just 0.1 millimeters thick.
  • The low penetration as well as the difficulties of exposure of all the points of the food’s surface pose major technical issues that hinder the effectiveness of using UV radiation for food preservation.
  • The limited penetrability of UV radiation limits the application to UV radiation in the food industry for disinfection of the air, the surface of equipment, as well as water, which could trigger oxidative changes.
  • Because of the lower effectiveness in penetration, it is utilized to kill microorganisms that are present on the surface of foods (such as fish, meat bread, dairy beer, fruit juices, beers baked cakes, packaged sliced bread) and in room where the food is ripening (such as dry sausages and cheese) and also to disinfect air, water (such as an aseptic filling area) and equipment.
  • Generallyspeaking, the microorganisms’ resistance to UV radiation is as follows Gram-negative bacteria Gram positive bacteriayeasts
  • The UV resistance of microorganisms is based on the pigmentation of their respective microorganisms.
  • Cocci that make color-colored colonies is more resistant UV than colonial colonies without color.
  • The dark conidia of certain molds are extremely UV resistant.
  • Bacterial cells can be susceptible to being destroyed by UV and bacteriophages and mold spores are more resilient.
  • UV light can cause burns to the skin as well as cataracts in the eyes.
  • UV light creates free radicals, which cause cell damage. This could cause cancer.
  • The UV light also triggers melanin production in melanocyte cells, which causes sun-tanned skin.
  • UV radiation triggers the creation Vitamin D in the skin. The plastic (polycarbonate) sunglasses are a good source of UV radiation.
  • Overexposure to UV radiation in the eyes results in snow blindness. This is particularly a danger at sea, and when the snow falls over the land.

Source of Ultraviolet Irradiation – Germicidal Lamps

  • The most common source of UV radiation in the food industry comes due to quartz-mercury vapor lamps, or mercury lamps that operate at low pressure that emit radiation at 254 nm.
  • The light emitted by these lamps contains light rays that are visible as well as those in the erythemic spectrum, which may cause irritation on the mucous membranes and skin.
  • Lamps are sold in different sizes shapes, shapes, and powers.
  • The more recent models release small amounts of Ozone.

Factors Influencing Effectiveness

It should be noted that direct rays are the only ones efficient unless they are reflected by special reflectors and even then their efficiency decreases. The elements that affect the effectiveness of ultraviolet radiation are the following:

a. Time

  • The longer duration spent in exposure to a certain concentration greater the effectiveness of the treatment.

b. Intensity

  • Intensity of light hitting an object will be dependent on the brightness that the lamp has, its distance between it to its object and the nature and amount of interference material within the direction of the radiation.
  • The intensity is bound to rise with the brightness from the bulb. The intensity is typically measured in microwatts/square centimeter (m W/cm2 ). The amount or the dose of radiation actually taken up by an organism or product, is expressed as the product of duration and intensity.
  • In the shorter distances that are common in industrial use The intensity of radiation vary in inverse proportion to the how far away from the source. A lamp is 100 times more effective at killing microorganisms in 5 inches and 8 feet away from the object that is irradiated.
  • The humidity above 80 percent will definitely decrease the penetration of air, however humidities less than 60 percent do not have any effect.

c. Penetration

  • The form and nature of the object or the material that is being irradiated can have a significant influence on the efficiency of the procedure.
  • Penetration is decreased even with clear water, which has a protective effect on microorganisms.
  • Mineral salts that dissolve, particularly that of iron, as well as cloudiness significantly hinder the effectiveness of radiation.
  • Even a small amount of fat or grease cut off the rayons. It is impossible to penetrate through the opaque material.
  • Thus, the rays impact only the surface of the majority of food items directly that are exposed to the lamp. They are not able to penetrate into microorganisms in the food.
  • The lamps are able but they also reduce the amount of living organisms that live in the air around the food item.

Action on Microorganisms

  • As stated earlier, it is the strength of radiation that reach the living organism and the duration at the time they are active and the place of the body determine the effect of germicide.
  • Every microorganism has its own distinct resistance to UV radiation. It can be different based on the growth stage and the state of health that the cells are in. It may take as much as five times the amount of exposure to kill vegetative cells of certain bacteria as compared to others however, the amount of killing dose is not significantly different between various species.
  • Amount of radiation required to kill various microorganisms could differ.
  • The position of the organism during tests can have significant influence. For instance, 97- 100 percent Escherichia bacteria in the air were killed within 10 seconds at 24 inches with a 15-watt light, however, 20 seconds at 11 in was needed for the growth of bacteria to grow on the surface of the agar plate.
  • The clumping or capsulation of bacteria boosts their resistance.
  • Bacterial spores typically receive between to five times the exposure as the vegetative cells.
  • Certain kinds of pigmentation provide a protection. Generally speaking, yeasts are two to five times resistant to bacteria, however certain types of yeasts are easy to kill.
  • The mold’s resistance is believed to be anywhere from 10 to 50 times the resistance of bacteria.
  • Pigmented molds are stronger to nonpigmented molds. the spores are more resilient than mycelium.
  • The killing effects of ultraviolet rays is generally explained using”target theory,” or “target theory,” which is discussed in the discussion on the ionizing radiation.

Applications in the Food Industry

  • The application of ultraviolet radiation within the industry of food will be reviewed in relation to the preservation of particular food items. Examples of the effective usage of these rays include the treatment of water used in drinks; the aging of meats treatments for knives to slice bread treatments for cakes and bread packaging bacon slices and sanitizing eating tools; prevention of the development of film yeast on vinegar, pickle sauerkraut and pickle vats; killing sugar crystals as well as in sirups, storage and packaging of cheeses; prevention of the growth of mold on shelves and walls.

2. Ionizing Radiations

  • Ionizing radiation can be heard at an amplitude of 1018 Hz, and is able to carry enough energy to release electrons out of molecules.
  • The following radiation sources are allowed to be used in food processing in accordance with the Codex General Standard of Codex Alimentarius Commission: (i) The radionuclide cobalt-60 , also known as cesium-137. (ii) High-energy electrons. Electrons are produced by a machine with the maximum energy that is 10,000,000 electron volts (MeV). They are a kind of B-rays. (iii) The X-rays are generated by a device at the maximum energy that is 5 MeV.
  • The radiations do not possess enough energy to influence the neutrons within food molecules’ nuclei, consequently, they aren’t capable of causing radioactivity in food.
  • Also this is because none of these sources can produce radioactive isotopes found in food. The ionizing radiations have enough power to transform electrons in food molecules into Ions (electrically charge particles) and free radicals (reactive substances with electrons that are not paired) that include oxygen radicals with high energy, which destroy or harm microorganisms.
  • The possibility of Ionizing radiation in food items is based on the efficient inhibiting of DNA synthesizing. In the right doses, it is not likely to have any adverse effects on food products.
  • The dose of radiation is determined by the radiation’s energy source as well as the duration of exposure. The ability of microorganisms and microorganisms to absorb radiation dose is determined by their size as well as their water content.
  • The doses of radiation are directly linked to the degree of destruction of pathogens causing bacterial infection. Yet, D10 values (irradiation doses needed to induce a 1 log reduction in the number of cells) that are applied to food products are based on density as well as antioxidant levels as well as the moisture content as well as other food ingredients.
  • External factors, like temperature, as well as whether oxygen is present or not are also a factor in the impact that radiation can cause.
  • The ionizing radiation utilized in food irradiation is restricted to electromagnetic radiation of high-energy (gamma radiation from 60Co, and X-rays). They are selected due to (i) they create desired effects on microorganisms (ii) they don’t cause radioactivity in food and packaging material, (iii) they are accessible in sufficient quantities and prices that permit commercial use of the procedure and (iv) the radiation absorbed by X-rays or Gamma rays into the material occurs in a variety of ways. The maximum usable depth for the gamma radiations in water-equivalent materials is 3.9 cm. The X-rays’ diameter it is 23.0 cm.

Types of Ionizing Radiations

Ionizing radiation is defined as the x-rays and gamma-rays beta or cathode rays protons, neutrons and particles of alpha. Neutrons can cause residual radioactivity in foods and alpha particles and protons have a limited penetration. This is why these rays are not suitable to use for food preservation , and therefore will not be discussed.

A. X-rays

  • X-rays penetrate the electromagnetic field that are generated by the bombardment of a target made of heavy metal with cathode-rays in the tube that is evacuated.
  • They are not considered as economically feasible for the food industry.
  • Gamma rays and X-rays and cathode rays are all equally effective in sterilization , with the same amounts of energy that are absorbed.
  • Gamma and X-rays are well-absorbed, whereas cathode radiations have relatively low penetration.
  • The main drawback for the application of xrays in preservation of food is the lack of efficiency and thus the high cost of their production. For the only 3-5% of energy used is utilized for the production of radiations called x-rays. Because of this, the majority of recent research has focused on the use of gamma and cathode radiations.

B. Beta rays

  • Beta Rays are electron-based streams (beta particles) released from radioactive materials.
  • Electrons are tiny, negatively charged particles with uniform mass , which form an element of the Atom.
  • They are slowed by electric and magnetic fields.
  • Their penetration is determined by how fast they strike the target.
  • The greater the charge of electron is, the more deeply it penetrates.

C. Gamma rays

  • Gamma rays resemble that of x-rays however they originate from the by-products of nuclear fission or from imitations of by-products. Cobalt 60 and cesium137 have been utilized for the production of these rays for the majority of experiments to date however, with cobalt 60 being most likely one for commercial applications.
  • Gamma rays emit everywhere and penetrate the skin. They are constantly emitted and originate directly from sources of radioactivity.
  • Gamma radiation requires more protection from radiation to ensure workers are protected. The tests conducted so to date on both animals and human volunteers haven’t revealed any negative effects from consumption of radiation-treated foods.

Source of Gamma Rays

Gamma Rays are the primary source of gamma rays. are

  • radioactive fission product of cobalt and uranium
  • The coolant circulated within nuclear reactors and
  • other fuel elements that are used in the operation of the nuclear reactor

Penetration of Gamma Rays

  • Gamma rays are able to penetrate However, their efficiency diminishes exponentially as they get deeper.
  • They are believed to be effective for up to 20 cm in the majority of food items however, the depth of this effect will be dependent on the duration of exposure.

Efficiency of Gamma Rays

  • The efficiency of Gamma Rays are quite low when compared with cathode Rays.
  • The maximum is 10-15% efficiency can be estimated for gamma radiation.
  • Gamma-ray sources that emit radioactive radiation diminish steadily, and diminish over time.

D. Cathode rays

  •  Cathode rays are a stream made up of electrons (beta particles) emanating from the cathode of an evacuated tube. In the real world they are accelerated using artificial methods.
  • The use of cathode radiation pose less health risk than Gamma rays because cathode rays have a directional nature and are less penetrated, they can be shut off to perform maintenance or repair work, and do not pose a danger of radioactive substances following an explosion, fire or any other disaster.

Source of Cathode rays

  • Cathode rays are usually stimulated by electrical devices that are specially designed. The higher the acceleration (i.e. more meV) the greater the penetration into food.

Penetration of Cathode rays

  • Cathode rays in contrast have a low penetration they are only effective at 0.5 centimeters per megavolt in the event that “cross firing”, that is, irradiation coming from opposite sides is used.
  • The absorption dose in the material is not an evenly decreasing percentage with depth , but rather increases until it reaches a peak at the depth of about 1/3 of total penetration , and the absorption dose decreases until zero.

Efficiency of Cathode rays

  • Since cathode rays are directed and directional, they are able to strike food and thus are utilized more effectively than the gamma rays that are continuously emitted throughout the world from radioactive sources.
  • Different estimates of the maximum effectiveness of the utilization of cathode radiation range from 40 to 80 percent according to the shape of the material being irradiated.

Factors Affecting Inactivation of Microorganisms by Irradiation

The bactericidal effectiveness of a dose of radiation is based on the following factors:

  • The type and species of organism: Microorganisms significantly vary in the sensitivity to radiation. Different species and types of microorganisms are tolerant to radiation. The most frequent food spoilage and many foodborne pathogens from different species are usually sensitive to radiation and are able to be killed with low or medium doses of radiation that range from 1 7 and 7 kGy. The molds have a greater sensitivity radiation than yeasts, and they are more sensitive to radiation than bacteria as are bacteria more tolerant to radiation than viruses. Gram positive bacteria have a higher resistance radiation than Gram-negative ones or cocci. They are also more unaffected by radiation than rods. Lethal doses for microorganisms and insects are according to insects, around 1 kGy; moulds, yeasts and bacteria, 0.5-10 kGy; bacterial spores, 10-50kGy and viruses, 10 to 200 kGy. Higher doses for destroying spores (above 10-kg) are not included in foods , except for vegetables and spices.
  • The numbers of organisms (or spores) originally present: The greater the number of organisms there are in the environment, the less effective the given dose will be.
  • The composition of the food: microorganisms is sensitive to radiation when exposed to buffer solutions. They are more sensitive to radiation than organic substances (such such as protein) with solutions. Organic compounds exhibit protective effects against radiation. Antimicrobial agents, like Nitrite, can increase the resistance of microorganisms to radiation.
  • The presence or absence of oxygen: TThe effects of oxygen that free oxygen has is dependent on the individual and can range from no impact to a sensitization of the body. Inexpensive “side reactions,” which will be further discussed and are likely to become more intense when oxygen is present and are less likely in an atmosphere or a vacuum of nitrogen.
  • The physical state of the food during irradiation: Temperature and moisture alter the organisms in various ways.
  • The condition of the organisms: Age,  temperatures of growth, temperature of sporulation, as well as the stateeither spore or vegetative–can influence the sensitivity of organisms. The method of radiation used and within limits the acidity of food appear to have little effect on the dose required to activate the organisms.
  • Type of Radiation: Gamma rays are a viable option for efficient and efficient application in food preservation when compared with X-rays or b-rays. Cobalt-60 is used primarily as a source of gamma-rays in food radiation because of its availability and affordability. The effectiveness of antimicrobial the ionizing radiation is increased as the dose is increased.

Mechanisms of Microbial Inactivation by Irradiation

  • If microorganisms and foods are exposed to radiation ionizing, molecules and atoms in food absorb energy. They remove electrons and creates negative and positive Ion Pairs.
  • The electrons released are stimulated, and therefore can take electrons of other elements and transform them into Ions.
  • Ionization and energy energization could negatively affect the normal functioning in biological processes.
  • The effects that radiation has on living material can be both indirect and direct. The direct impact results from the removal of electrons due to the radiation’s energy deposition on target molecules like DNA.
  • The indirect effects are caused by the formation of reactive diffusible free radicals because of the radiolysis of water, including the hydroxyl radical (OH) and electrolyte hydrated (e) H atom the hydrogen peroxide (H2O2) along with the hydrogen radical (H).
  • H2O2 and HOH are both powerful antioxidants, while the H radical can be a powerful reducer. The radicals H+ andOH are extremely reactive they cause oxidation and reduction on substances and also the breaking of carbon-carbon bonds as well as bonds between other molecules, as well as double and single strands of DNA, particularly in the sugar-phosphate bond. In addition, the radicals can change the bases, such as thymine to dihydroxydihydrothymine.
  • The main targets of radiation are nucleic acid and the lipids of the cell membrane. Ionizing radiation can cause damage to cell membranes as well as other cell structures (sublethal damage).
  • Changes in membrane lipids, especially those with polyunsaturated lipids leads to disruption of membranes and affects the various functions of membranes including the ability to permeabilize.
  • The function of membrane enzymes can affect membrane enzymes too. Chromosomes in bacteria are highly vulnerable to free radicals and damaging them can cause death.
  • Ionization radiations alter cell DNA structures, by breaking certain bonds. This blocks replication and other functions of DNA.
  • The capacity of bacteria to repair damaged cells gives them protection against radiation. The ability of bacteria to repair cell damage varies significantly.
  • The effects of radiation can alter certain microbial cells, resulting in an increase or decrease in pathogenicity, through the production of toxins or the loss of certain metabolic functions.
  • The rate at which microorganisms die caused by radiation follows a similar straight lines as it is the case with the temperature destruction curve.

Effects on Foods

High doses of radiation that cause sterilization are known to cause unfavorable “side reactions,” or secondary changesin a variety of types of food items, causing unpleasant colors, odors, flavors, and even physical properties. Some of the changes caused in food items that are caused by radiation doses that sterilize are

  • in meat, an increase in pH, the destruction of glutathione, as well as an rise in carbonyl compounds hydrogen sulfide, as well as methyl mercaptan.
  • in lipids and fats degradation of antioxidants that are natural in lipids and fats, oxidation that is that is followed by partial polymerization and an increase in carbonyl compounds and
  • Vitamins, reduction in the majority of food items the levels of thiamine the pyridoxine chemical, as well as vitamins B12 , C, D, E, and K. Niacin and riboflavin are stable.
  • The lower the dose of radiation the lesser the frequency of adverse effects on food. Destroying many of the enzymes in food requires five to 10 times the dose of radiation required to kill the microorganisms. The enzyme action can continue even after all microorganisms have been eliminated unless a specific blanching procedure was performed prior to the radiation.

The main effect on quality of food is the depletion of vitamins. But, the overall nutrition of food that is irradiated will be comparable to the food that is processed using other methods to attain the same stability on shelves. There isn’t any evidence that radioactivity is produced by electron beams lower than 11 meV or cobalt 60 gamma rays.

Processing of Foods Before Irradiation

There are several steps to be processed before food items are exposed to radiation, as is the case for freezing or canning food items.

  • Selection of foods: Foods should be of a fresher variety with a high-end overall quality.
  • Cleaning of foods: The visible particles and dirt must be eliminated. This will decrease the initial amount of microorganisms that will be destroyed by radiation treatment.
  • Packing: Foods can be packaged in containers that guard against post-irradiation-induced contamination. Cans are the most effective in the moment using plastic containers. Clear glass containers exhibit colors changes when exposed to radiation doses of 10 kGy or more that might be unsuitable.
  • Blanching: Irradiation doses that sterilize do not suffice to destroy the enzymes in food that are natural to us. In order to prevent undesirable effects of radiation, it is essential to eliminate the enzymes. The most effective method seems to be heat therapy like the blanching of vegetables or the gentle heating of meats prior irradiation.

Application of Irradiation in Food Industry

Three distinct areas that are part of electromagnetic spectrum can be utilized in food microbiology: microwaves UV radiation and gamma-rays. The fields of application for radiation within the food industry include the extension of shelf-life, disinfection as well as decontamination and quality improvement.

  • Disinfection: Disinfection is among of the most important procedures for food processing and chemical treatments are typically employed to treat this issue. Disinfection is a method of controlling microorganisms as well as insects present in fruits, with doses as high as 3 kGy. A small dose of 0.15-0.50 kg can harm insects at different stages of development. These insects could be found on food items. Radiation may affect the insect’s sexual viability and its potential of maturing into an adult.
  • Shelf-Life Extension: One type of extension to shelf life is to stop the growth of onions, potatoes and garlic, at 0.02-0.15 Kg. Another method is to slow the ripening process and the senescence of certain exotic fruits (such as avocados, bananas papayas, mangoes, and papayas) at 0.12-0.75 kg. It also extends the shelf-life of perishable items (such as meat, poultry and seafood) by destroying spoilage microorganisms.
  • Decontamination: Radiotherapy can lower the amount of microbial matter. One type of decontamination involves the use of a lower amount (1.0-2.0 kgy) to pasteurize food items like poultry, seafood and beef. Another option is more powerful (3.0-20 kGy) that is used to sterilize food items (such for sterilizing of poultry, spices or seasonings).
  • Product Quality Improvement: Higher juice yield is possible if the fruits are first exposed to radiation at an intensity of around kGy, thereby enhancing the recovery of the product. The gas-producing elements in soybeans could be significantly diminished by a sequence of the soaking, germination, and irradiation and drying the beans. It is possible to need a dose up to 7.5 Kilograms to have the greatest effect. It also helps reduce the requirement for chemical substances used in preservation of food, like salts and nitrite. In addition, irradiation will not leave chemical residues on food products.
  • Minimize food losses: Radiation disinfection and shelf life extension can decrease food freshness loss and freshness of food items. The majority of postharvest losses resulting from insects can be prevented and minimized by radiation treatment of food items such as grains fruit, tubers, and grains. Also, the shelf-life of some fruits and tubers may be extended with delay ripening or inhibition of sprouts. Another possible benefit of the use of irradiation on fruit is the improvement in the juice yield after processing of various products.
  • Improve public health:  Some foods, particularly muscles, are infected by pathogenic microorganisms and parasites. Decontamination of fresh foods through irradiation could alleviate the health of people. Salmonella is the main cause of foodborne illnesses in poultry products. Radiation is used up to 3.0 kGy to clean poultry, and as high as 1.0 kg to combat Trichinella spiralis that can be found in carcasses of animals. The use of irradiation can also be a means to ensure the hygiene of food products.
  • Increase international trade:  A lot of fresh foods aren’t eligible from international trade because of (i) the infestation of insect pests, (ii) infection by microorganisms as well as (iii) their shelf-life. They limit long-distance shipping. The effects of radiation can boost or enhance the flow of fresh food across international markets. It can provide an effective process for quarantining against food spoilage and pathogens or assist in prolonging the shelf-life of food items.
  • Alternative to fumigation of food:  Many chemicals (such as Ozone, ethylene dibromide methyl bromide, and even ethylene oxide) are employed to control the fumigation of food ingredients and food products. Chemical disinfection procedures is rapidly decreasing because of their environmental and toxic impacts, like the poisonous characteristics of the ethylene oxide, and the ozone depleting effects of the fumigant ethylene dibromide. Irradiation at low doses of 0.2-0.7 Kgy is a good way to control insects that infest grain and other stored goods.
  • Increase energy saving:  Energy used in radiation of food is minimal when compared to canning, refrigeration or freezing storage. The energy consumed by raw frozen cut-up poultry is 46 600 kg1 (3-5-week freezer storage) and for canned poultry, it is 180 kg1. For comparison, refrigerated and Irradiated raw cut-up chicken requires 17 860 kg1 of kJ . Additionally, refrigerants may lead to higher prices for refrigerated food in the near future, so the combination of irradiation and chilling is a great option for energy savings during the process of processing food. Reduced energy consumption could also aid in the an overall reduction in pollutant emissions resulting from burning products from traditional fuels.

Application of Irradiation on Foods

Irradiation is a method to neutralize the spoilage process and to kill pathogenic microorganisms that are present in food items. It also kills insects’ eggs and larvae that are found in fresh vegetables and fruits. Its capability to neutralize pathogenic bacteria in frozen foods is distinctive. Since irradiation is a pasteurization process, food stays in the same condition following irradiation and frozen foods remain frozen, food items that are raw remain in their raw state, and volatile aroma substances are preserved. The process of irradiation can have a variety of applications in the food processing industry that enhance the quality and safety or extend the duration of food items. Due to the physical properties of ionizing radiations no radioactivity is induced by irradiated food items.

1. Plant Foods

  • Plant tissues show a brief increase in ethylene production and respiration when radiation doses are low. The rate of ethylene production increases linearly with increasing dose radiation.
  • Ethylene production increases also when food items are exposed to radiation greater than 1 kGy. Fruits are afflicted with physiological problems (such as softening of tissues and an enzyme browning) after exposure to radiation above their tolerance limits.
  • Tissue softening occurs due to (a) the partial depolymerization cells wall polysaccharides, which is mainly pectins and cellulose (b) damage to the membrane of cells.
  • The browning of enzymes is a sign of cell lysis as well as enzyme release due to the damage to the membrane of cells, bringing phenolic substrates into contact with polyphenoloxidases.
  • The damage to the cell membrane can cause (i) losing intracellular water (ii) the cell’s swelling (iii) the release of enzymes and (iv) the oxidative attack of the polyunsaturated fatty acids in membrane lipids.
  • The reduction in oxidation is possible by using radiation in an environment with a low oxygen content however this can reduce the effectiveness of treatment.
  • A carbon dioxide (CO2) atmosphere guards plants’ tissues from the loss in membrane protein. Therefore, low dose irradiation with a modified atmosphere could be utilized to manage microorganisms and slow the ripening of vegetables and fruits.
  • The synergistic effect of irradiation in conjunction with high CO2 is employed to stop the growth of mold on plant food products.
  • A degeneration that is caused by Rhizopus stolonifer or Botrytis cinerea in strawberries can be prevented by packaging with 77 percent O2, 20 percent CO2 73% N2 and the irradiation of 1 kGy.

2. Spices

  • Spices can be highly contaminated by pathogenic microorganisms. The most common microorganisms found in pepper include Clostridium, Staphylococcus, Bacillus Aspergillus and Fusarium.
  • The dose 2.5 kGy can reduce the amount of mold and bacteria, and 7.5 mg eliminates the population of mold in whole or ground pepper.
  • Garlic treated with approximately 0.2 milligrams of kGy can stop sprouting and decrease weight loss in storage.

3. Fruits and vegetables

  • In addition to the flavor and odor change in some foods that are irradiated, negative effects could occur in vegetables and fruits.
  • One of the biggest issues is the softening of these food items through the degrading of pectin by radiation as well as cellulose and polysaccharides that form the structural part of the food.
  • The shelf life after harvest of fruits (such as blueberries, cherries and cranberries) can be extended by a small doses of irradiation ranging between 0.3 to 1.0 Kg.
  • Doses up to 0.1 kg may have no influence on the firmness of apple carrots, beets and beets However, the speed of softening is increased in higher doses.
  • The efficient control of the rotting and sprouting of fruit and vegetables can be achieved by the irradiation rate of around 1.0 Kgy, however significant tissue softening may be observed.
  • Irradiation with doses ranging from 1.0 up to 3.0 kGy is effective in prolonging the strawberry’s shelf life without any quality change. The effects of radiation can increase the strawberry sweetness by reducing the acidity titratable.
  • The treatment of vegetables and fruits by irradiation is an alternative to the use of methyl bromide.
  • The depolymerization process of carbohydrate polymers by irradiation for example, cellulose and starch could little or not increase the sugar amount.

4. Cereals and grains

  • They are treated using small doses of radiation to kill mold. The dose of 5 kGy destroys the spores of a variety of molds.
  • Irradiation doses that fall within ranges of 0.2-1.0 Kgy are efficient in preventing the spread of insects in cereals. Apart from its protection ability against insects and microorganisms radiation also impacts the qualities of cereal grains.
  • The viscosity of the flour decreases as the irradiation dose. The bread’s overall quality wheat is significantly diminished by irradiation ranging of 1.0 to 10 kGy.
  • The effects of radiation are significant in the cooking characteristics of spaghetti. When you irradiate the flour with more than 1.0 Kgy can lead to lower scores for firmness, stickiness and bulkiness of dough due to the degrading of both gluten and starch.

5. Animal Foods

  • Irradiation can be effective in preventing or slowing the spoilage of microbials in fresh poultry and fresh meats.
  • The irradiation of meat at doses ranging from 0.25 to 1.0 Kgy in conditions of aerobic extends the shelf life of meat, however it increases the rate of rancidity.
  • Odor and flavor are developed when meat is stored in a room that has been irradiated. Peroxide and fat bleaches accumulation are more rapid in the meat that has been irradiated.
  • Doses of radiation upwards of 2.5 kGy are used to control Salmonella, Campylobacter, Listeria monocytogenes, Enterococcus Faecalis, Staphylococcus aureus as well as E. coli in poultry and meats.
  • The doses that exceed 2.5 kGy can alter the taste, odor and the color of the meat, but the effects can be reduced by using radiation at lower temperatures or without oxygen.
  • The treatment of irradiation isn’t able to prevent chemical changes that occur in meats that can negatively impact consumer satisfaction, such as oxidation of the pigment to produce gray or brown discolorations as well as the oxidation and degradation of lipids that cause off-flavors when exposed to oxygen from the atmosphere. Vacuum packaging coupled with radiation of meat could prolong the shelf-life of the meat.

(a) Poultry

  • Radiation doses ranging from 1.0 and 2.5 kGy to poultry are effective in the fight against Listeria, Pseudomonas aeruginosa, E. coli, Serratia marcescens, as well as S. S.
  • The doses are able to prolong shelf-life of poultry that has been irradiated by chill temperatures. These doses could create a radiation odor as well as color and flavor changes.
  • The color of the poultry is based on three aspects: the concentration of hem pigments, chemical composition of these pigments, as well as the physical properties of light scattering of the meat’s structure.
  • In general, radiation to poultry in an atmosphere of CO2 or a vacuum caused the greatest harm on microorganisms. Bacteria are less tolerant to radiation if the poultry is packed in N2.

(b) Beef

Pseudomonas, Enterobacteriaceae, and Brochothrix thermosphacta are all reduced by irradiation of the beef without altering the sensory properties. The irradiation process of beef can have the these effects:

  • it kills pathogenic bacteria like E. coli O157: H7, Salmonella, S. aureus it inactivates pathogenic bacteria, such as S. aureus, E. L. monocytogenes.
  • It is not the case that food items are radioactive.
  • it doesn’t change the flavor, aroma, and texture of ground beef.
  • there is no detectable increase in the risk of cancer associated with long-term consumption of radiation-pasteurized meat;
  • It is a healthy and nutritious food source;
  • it increases the microbiological security. However, meats that have been irradiated may be significantly more tender and tender than meats that have not been irradiated.

(c) Processed meats

  • A large amount of Nitrite needed in the curing process of meats may be diminished by irradiation. This is decreasing the production of the nitrosamines.
  • Enterobacteriaceae can be effectively killed through irradiation of meat products at doses of approximately 2.0 kGy.

(d) Fish and fish products

  • The elimination of pathogenic microorganisms as well as the lengthening of shelf lives of fish in fresh form can be accomplished with minimal doses of approximately 2.5 kGy.
  • The typical doses of up to 2.5 kGy are usually sufficient to control spoilage bacteria and prolong the shelf-life of fish that is fresh. In generally, the shelf-life extension upon irradiation is dependent on the conditions of radiation and storage, and can vary in different kind of species.
  • Radiation can have the following effects on fish and the products of fish:
    • The total volatile nitrogen formation is less in fish that have been irradiated;
    • A greater rise in the thiobarbituric acid levels that may continue to increase gradually during storage
    • shortchain fatty acids decrease after radiation, while other fatty acids increase;
    • Thiamine loss is more severe when doses are higher 4.5 while riboflavin is not affected.
    • doses greater than 3.0 kGy can cause a decrease in tocopherols.

Effects of Irradiation on Food Components

1. Effects on proteins

  • Proteins as well as the other compounds that are nitrogenous are prone to the effects of radiation in foods. The products of irradiated amino acid proteins, peptides and peptides are NH2 CO2, H2S, carbonyls and amides.
  • Free radicals that react with proteins could cause cracks in the chain of proteins or alter secondary and tertiary structures of proteins. These changes or breaks could be fatal to living organism but would not impact the nutritional quality that the foods contain.
  • The low doses of radiation can result in molecular uncoiling, unraveling, coagulation breaking, and breaking between amino acids.
  • The most significant effects are centered around the hydrogen bonds and sulfur links. In the case of 10 kGy radiation the amount of free amino acids can increase in food items.
  • The effects of radiation can result in the an unfolding of the protein molecule and causes the formation of reaction sites. It also alters the properties of proteins that are functional.
  • For eggs, doses that are required to achieve Salmonella reduction can cause negative side effects like loss of viscosity of the white as well as off-flavors present within the yolk.
  • The irradiation of eggs using 6 kGy causes the appearance of a thin layer of water, which could be due to the degrading of Ovomucin (main ingredient in the thickening of egg albumin).
  • The time for coagulation of rennets in casein increases in milk when milk is exposed to radiation and also decreases the temperature stability of casein.
  • The development of off-flavors at the highest doses occurs due to an increase in benzene sulfur compounds, and phenols by phenylalanine and tyrosine and methionine.
  • Flavor variations and off-flavors look like the burnt taste after radiation of milk.
  • The irradiation process of cheese typically produces smokey off-flavors.
  • The irradiation treatment of soft cheese in a dose of between 1-2 Kg is enough to eliminate food-borne pathogens, and it doesn’t affect the flavor of the food.

2. Effects on carbohydrates

  • Reaction of radicals hydroxyl and starch creates formic acid, as well as ketones and some aldehydes.
  • Radiation can break down the high-molecular-weight carbohydrates down into smaller components, which can lead to depolymerization. This is the process responsible for the softening process of vegetables and fruits by the breaking down of cell wall components such as pectin.
  • However, it can be beneficial or detrimental depending on the need. For instance, it could be beneficial in reducing the yields of juice as well as in reducing drying and cooking time of dehydration.
  • The treatment of wheat with 0.2-10 kgy raises the water-soluble content of the grain, reduction of sugars by 5 to 92 percent. These modifications are extremely beneficial in the production of bread aroma and flavor through reducing sugar-amino acid reaction.
  • The irradiation of carbohydrates that are pure produces degradation products that are cytotoxic and mutagenic. Sugars are hydrolyzed and transformed by gamma irradiation.

3. Effects on lipids

  • The radiolytic products that are formed by fats are usually not the result of the reaction of disrupted water molecules. Radiation rays interact directly with lipid molecules and create cation radicals or to stimulate molecules of lipids.
  • They can also produce an oxide of lipids (which cause off-odors and unpleasant tastes) and small quantities of aldehydes, fatty acids esters, ketones and other compounds.
  • The radiation of fats and lipids causes the creation of carbonyls, as well as other products of oxidation including peroxides.
  • The most important organoleptic reaction to the foods containing lipids is the formation of rancidity. The radiation process can cause creation of oxides of lipids through reactions of the lipids within food items together with oxygen radicals.
  • Radiation triggers the autoxidation process of fats. This gives the appearance of rancid off-flavors as well as taste to food products and can be a cause of poisons related to lipids.
  • Fats that are highly saturated can be more easily to be oxidized than fats with lower levels of unsaturation. Radiolytic decomposition of unsaturated fat acids in lipids break double bonds. This process leads to the formation of volatile compounds that are responsible for off-odors.
  • Peroxides are formed as well as volatile compounds, as well as runningcidity may be observed.
  • Because of this, certain food items (such as fish that is fatty meat, fatty fish, and a few dairy products) aren’t irradiated. The oxidation process can be stopped by the removal of oxygen via vacuum or altered atmospheric conditions.
  • The reduction of temperature and oxygen levels will reduce the production of oxides after irradiation. Incorporating antioxidants and carnosine (such such as Vitamin E) to food items can reduce the formation of oxides during radiation.

4. Effects on vitamins

  • Certain vitamins (such as the riboflavin vitamin, niacin along with vitamin D) are quite immune to radiation. However, vitamin B1, A (thiamine) E, and K are comparatively sensitive.
  • The sensitivities of the people affected depend on the degree of complexity in the food chain, whether the vitamins are soluble in fats or in water as well as the conditions where irradiation takes place.
  • The degree the vitamin C E degradation and destruction of K is dependent on radiation dose. The loss of vitamins is minimal with lower doses of radiation.
  • In solution, ascorbic acids are very vulnerable to radiation. However, in the fruits and vegetables, it is solid at very low doses of treatment.
  • Vitamins that are antioxidant-rich, especially those with action (such as vitamins B, A C, E and K), pantothenic acid and the folic acid) are easily degraded when oxygen is present. It is important to keep in mind that vitamins also get destroyed by cooking and other preservation processes.

5. Effects on enzymes

  • Food enzymes should be deactivated prior to irradiation since these enzymes are less tolerant to radiation than microorganisms.
  • Typically, the inactivation of enzymes is done by heating. In general, the complete activation of enzymes is around 5-10 times the amount required to kill the microbial cells.
  • The D values for enzymes can be as low as 50 kGy. So, food products irradiated with radiation will be unstable when stored because of their vulnerability to enzymatic attack , compared to foods that are not irradiated.
  • Enzymes are influenced by indirect means by free radicals created within the phase of solvent.
  • So dilute solutions of enzymes are more sensitive to radiation as opposed to concentrated solutions. The natural environment in which enzymes are found such as in food, are comparatively resistant. The enzymes’ activity is not affected by very low dosages.

6. Packaging materials

  • The irradiation of food items in their packaging can reduce the risk of contamination after irradiation.
  • However, the effect of radiation on packaging materials and movement of the ingredients, like plasticizers, into food items should be taken into consideration.
  • PVC (Polyvinyl Chloride) (PVC) films that have been exposed to radiation doses that are high (20-50 kGy) boost the migration of dioctyl Adipate and plasticizers into food items (such such as olive oils).
  • These radiation doses are far in the higher range than what is normally recommended for food items. This raises the possibility of a issue with irradiation of food items within plastic packaging.
  • The plastic should be examined for the effects of radiation on the transfer of the plastic’s components into food products.
  • Radiation may also alter the structure and stability of certain plastics, rendering them unsuitable for exposure radiation.
  • Plasticizers made from Adipate are not powerful toxicants. However, they can have negative consequences on lab animals.
  • PVC plastics are extensively utilized There is a possibility of exposure to plasticizers through various sources. The negative consequences of the accumulation of doses from the various exposures on human health should be taken into account.

References

  • Food Preservation by Irradiation. (2016). Food Microbiology: Principles into Practice, 106–126. doi:10.1002/9781119237860.ch32
  • McGivney, W. T. (1988). Preservation of food products by irradiation. Seminars in Nuclear Medicine, 18(1), 36–45. doi:10.1016/s0001-2998(88)80018-7 
  • Andrews, L.S. et al. (1998). Food Preservation Using Ionizing Radiation. In: Ware, G.W. (eds) Reviews of Environmental Contamination and Toxicology. Reviews of Environmental Contamination and Toxicology, vol 154. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-2208-8_1
  • https://www.sciencedirect.com/topics/nursing-and-health-professions/food-irradiation
  • Kebede, Girma & Simachew, Ashenef & Disassa, Haimanot & Kabeta, Tadele & Zenebe, Tilahun. (2015). Review on Radiation as a Means of Food Preservation and its Challenge. 
  • Ganguly, Subha & MUKHOPADHAYAY, SUNIT & Biswas, Subhasish. (2012). Preservation of food items by irradiation process. International Journal of Chemical and Biochemical Sciences (International Scientific Organization, Faisalabad, Pakistan). 1. 11-13. 
  • https://www.osti.gov/servlets/purl/4529754
  • https://www.fda.gov/food/buy-store-serve-safe-food/food-irradiation-what-you-need-know#:~:text=Food%20irradiation%20(the%20application%20of,food%20safer%20for%20the%20consumer.
  • https://www.slideshare.net/hephz/preservation-of-food-by-radiation
  • https://uomustansiriyah.edu.iq/media/lectures/6/6_2021_11_04!11_38_13_AM.pdf
  • https://apps.who.int/iris/bitstream/handle/10665/38544/9241542403_eng.pdf
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