Lesson 10 Flashcards
Radiation
Radiation refers to the emission and propagation of energy through matter or space by electromagnetic disturbances. These forms of energy are found within the electromagnetic spectrum of radiation.
Microwaves
The microwaves travel in straight lines and pass through air, glass, paper and plastic, but reflected by metals. They are readily absorbed by water (polar molecule), causing it to vibrate. Heat is generated by the intermolecular friction generated from the vibrating water (polar) molecules in food. Microwaves are absorbed by food up to a depth of 5 to 7.5 cm.
Infrared energy
Can generate heat. They can reach temperatures above 100°C. Typical examples of infrared energy can be seen in ovens, toasters, and even those “infrared” lamps used to keep food warm.
Ionizing energy
Short wavelengths; X-rays, beta rays and gamma rays, which can be employed as energy sources in food irradiation, since they have good penetrating power.
Gamma radiation
is electromagnetic radiation that has very short wavelengths, similar to “short” x-rays. Isotopes such as Cobalt-60 and Cesium-137 emit gamma radiation as they disintegrate.
X-rays
are electromagnetic radiations that are highly energetic and of short wavelength. X-rays are produced by x-ray machines that emit a beam of fast electrons which hit a metal target in a vacuum. X-ray machines emit radiation only when the machines are turned on.
Electron Beam
can be produced with high-energy (speed) electrons or may also be generated by an electron beam accelerator. Electron Beam Accelerators need only electricity to operate and produce no waste materials
The Gray
is a unit of energy absorbed by a food irradiated with ionizing radiation. One thousand grays equals one kilogray (kGy). Most of the ionizing radiation processes permitted around the world involve absorbed doses of <10 kGy.
The Rad
this is another unit used to express the radiation absorbed dose (rad), where 100 rads = 1 Gy. However, the preferred unit is the kGy
Principle of preservation by ionizing energy
The ability of the absorbed quanta of energy to dislodge electrons from molecules with the concomitant creation of free radicals without inducing radioactivity in the food.
Requirements for becoming radioactive
To become radioactive, food would need to be exposed to a minimum of 15 MeV of energy. The energy output of Cobalt 60, Cesium 137, and e-beam accelerators is carefully regulated. The maximum energy outputs allowed are 5 or 10 MeV, which are too low to induce radioactivity in food.
Minimizing undesirable changes due to irradiation
- Irradiation in the frozen state: When water is frozen free radicals are produced at a lesser extent. The frozen state will delay free radical diffusion and migration to food constituents beyond the site of free radical production.
- Irradiation in a vacuum: Removing O2 from the system may minimize reactions; however removal of oxygen could also confer a protective effect on microorganisms.
- Addition of free radical scavengers: Ascorbic acid has a great affinity for free radicals.
Addition of free radical scavengers to food systems results in consumption of the free radicals via reactions between the scavengers and the free radical(s).
Irradiation doses (kGy) and purposes
–> < 10
inhibit sprouting of vegetables
kill insects eggs, larvae
slow ripening
inactivate parasites
–> 1 to 10
eliminate disease causing bacteria (Salmonella, E.coli O157:H7) and parasites
decrease or eliminate spoilage causing microorganisms (eg. mould)
–> 10 to 50 kGy
decontaminate food ingredients and additives
commercially sterilizes food
Radicidation
Radicidation is defined as a process designed to kill or inhibit disease-causing microorganisms (such as vegetative bacteria, yeasts, parasites) in food. Absorbed doses are often below 10 kGy. Foods that have been treated with a radicidation dose of ionizing energy must still be stored under refrigeration since all spoilage-causing microorganisms would not have been killed
Radurization
a form of radiation pasteurization, has as its objective the killing of the majority of spoilage-causing microorganisms and parasites so that storage life of the food can be extended during refrigerated storage. For example, treatment of fish to kill most of the spoilage-causing psychrotrophic bacteria would extend the storage life of the fish at refrigerated storage temperatures. Absorbed doses for radurization are below 10 kGy (often < 1 kGy).
Radappertization
equivalent to thermal commercial sterilization, involves treatment of food with an absorbed dose of ionizing energy such that disease-causing microorganisms and all spoilage-causing microorganisms capable of growing at the conditions of storage (e.g., at ambient temperatures) are inactivated. Absorbed doses of ionizing radiation are greater than (>) 10 kGy (usually 20, 30 kGy).
Note that in Canada, doses above 10 kGy are NOT permitted!
Safety and wholesomeness of irradiated foods: 4 principles
Radiological safety: ensuring that foods do not become radioactive during irradiation;
Toxicological safety: ensuring that production of toxic and possibly carcinogenic substances does not occur;
Microbiological safety: ensuring the efficacy of the radiation process with respect to the ability of the prescribed absorbed dose to kill disease-causing microorganisms that could be in the food.
Nutritional adequacy: ensuring that undue losses of nutrients do not occur as a consequence of treatment of food with ionizing energy; and
The irradiated foods which have absorbed a dose of less than ___ are wholesome and safe for long-term consumption.
10 kGy
__ or __ are particularly susceptible to oxidative reactions triggered by the radiolytic reactions and presence of free radicals.
Lipids, fats
To achieve an appropriate margin of safety, a __ or a __ radiation treatment would have to be applied to acid and low acid foods, respectively.
5D, 12D
Is it true that irradiation can mask food spoilage?
No
If vegetables were to be preserved with ionizing energy, they would first have to be ___, followed by _____
blanched with heat followed by treatment with ionizing energy to inactivate the microorganisms of concern.
Potential Applications of Radiant Energy
Astronaut food, eliminating salmonella from raw chicken, ground beef
In Canada, the use of ionizing energy for irradiation of food is considered as a ___ and is regulated under ___ of The Food and Drug Act and Regulations.
process, Division 26
Note that in addition to the mandatory basic labelling (Lesson 4), food treated with ionizing radiation MUST also include:
- A statement indicating that the food has been “treated by irradiation”, or “treated with radiation”, or”irradiated”.
- The “radura” symbol is also used to indicate that a food has been irradiated (see below).
- If an irradiated food is used as an ingredient of another food, it must be declared as “irradiated” in the ingredients listing only if it constitutes 10% or more of the final food.
Ionizing energy is characterized by..
having short wavelengths with high penetrating power
The energy emitted from these sources is measured in ___. Whereas, the amount of energy absorbed by the food is measured in ___.
MeV, kGy
Food will not become radioactive if the energy sources are operated at levels __
<15 MeV
The preservation principle of food irradiation involves a __ and __ effect on microorganisms.
direct, indirect
