Lecture 13: Irradiation Flashcards
are there commercial irradiation facilities in canada? what kinds are there?
no
irradiation facilities for research in industry, government, university
what are 2 types of irradiation technologies?
compare them
- man made radio isotopes
- electron accelerators
- both have comparable efficiency
- both must be installed in a shielded room to allow treatment to take place w/o compromising health of operators
- uses batch or continuous processes
describe the use of beta rays
- suitable for thin layers
- low energy
- uses electron accelerators (simple to operate and low cost)
describe labelling requirements for irradiated food
- identification of the irradiated food pdt or ingredient using the international symbol if it makes up more than 10% of the pdt content
- written statement that food has been irradiated
1 gray = ____ rad?
100 rad
rate the dose of radiation from smallest to highest
a) sprouting inhibited
b) lethal to insects
c) sterilization of MOs
d) no acute effects
e) lethal to humans
- no acute effects (1-100 rad)
- lethal to humans (100-1000rad)
- sprouting inhibited
- lethal to insects
- sterilization of MOs (1000 to 10^7 rad)
regulatory agencies determine what?
- which food may be treated by irradiation
- under what conditions
- for what purpose
- prescription of what type of information should be included in the label
in 1983, the codex alimentarious commission accepted what?
that foods irradiated up to 10kGy was safe and wholesome and toxicological testing was no longer necessary
what is the codex general standard of irradiated foods?
used for regulations of irradiated food for different countries
in 1986, why did RDA issue a regulation for a max dose of irradiation?
for:
- insect desinfestation
- ripening, growth and maturation inhibition
- applications to foods and specified radiation
- labelling with international logo
- use of radioisotopes
- no specific licensing for plant facilities
what is the USNRC?
united states nuclear regulation commission
what is AECB? what is it now named?
atomic energy control board
now named nuclear safety commission
what is dosimetry?
measurement of radiation dose
what is a dosimeter?
instrument for measuring dose
what is the role of dosimetry in food irradiation?
- to administer proper dose
- for commissioning food pdt through regulatory agency
- to establish quality control procedure in the food pdt plant
- to optimize configuration of the irradiation field after the installation of the irradiator or any changes that would occur in the irradiation facility
what is considered a low or low dose?
low dose: 0.6 to 10kGy
high dose: 5 to 50 kGy
in dosimeters, ceric ions are reduced to what?
cerous ions
what is one of the most useful reference dosimeters?
Fricke (ferous feric)
describe the Fricke ferous feric dosimeteter
- aqueous solutions of Fe+2 ions oxidized to Fe+3 ions with O2
- uses UV spectrophotometer to determine conc of Fe+3 at 305nm
- dose range of 0.02 to 0.4kGy
what are post harvest applications of radiation preservation?
- sprout inhibition of potato, garlic, onions
- insect desinfestation of fruits, grains, spices
- reduction of microbial load
- shelf life extension
- control of pathogenic organisms in food
what are benefits of radiation preservation?
- low energy consumption
- environmental cleanliness
- potential to reduce use of fumigants and pesticides
what are advantages of irradiation?
- killing microbial contaminants
- sterilizing or killing adult insects, larvae and eggs
- can be applied to fruits in a fresh state
- physical process
- high reliability
what are effects of radiation on polysaccharides?
partly depolymerized cellulose, pectin and starch
what are effects of radiation on proteins?
- they are less affected although reduction of disulfide bonds may lead to inactivation of active site and conformational changes in enzymes
what are effects of radiation on nucleic acids
- NAs are main targets of free radicals generated by gamma rays
what are the principal targets of gamma rays?
- nucleic acids and membrane lipids
- alteration in DNA
- alteration in membrane lipids
how do gamma rays affect DNA
- affecting gene expression
- affects biosynthesis of some enzymes
- interferes with cell division
how do gamma rays alter membrane lipids?
leads to perturbation of membrane functions and permeability
as gamma ray energy increases, how does the relative contribution to ionization change? (compton effect)
increases, then decreases slowly
as gamma ray energy increases, how does the relative contribution to ionization change? (for pair production)
increases slowly
gamma rays interact mainly with what?
water molecules
what does the interaction of gamma rays with water cause?
- production of OH and free radicals
- radicals react with O2 to form other radicals (peroxy or hydro-peroxide radicals)
- interaction of free radicals with organic molecules of food
in the ionization or radiolysis of water, what rxns take place?
- H2O + E –> H2O* (excited water)
- H2O + E –> H3O+ + e
- H2O* –> OH. + H. (free radicals)
- OH* + OH* –> H2O2 (H peroxide)
