Lecture 13: Irradiation

Question 1

are there commercial irradiation facilities in canada? what kinds are there?

Answer 1

no

irradiation facilities for research in industry, government, university

Question 2

what are 2 types of irradiation technologies?

compare them

Answer 2

1. man made radio isotopes
2. 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

Question 3

describe the use of beta rays

Answer 3

• suitable for thin layers
• low energy
• uses electron accelerators (simple to operate and low cost)

Question 4

describe labelling requirements for irradiated food

Answer 4

• 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

Question 5

1 gray = ____ rad?

Answer 5

100 rad

Question 6

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

Answer 6

1. no acute effects (1-100 rad)
2. lethal to humans (100-1000rad)
3. sprouting inhibited
4. lethal to insects
5. sterilization of MOs (1000 to 10^7 rad)

Question 7

regulatory agencies determine what?

Answer 7

• 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

Question 8

in 1983, the codex alimentarious commission accepted what?

Answer 8

that foods irradiated up to 10kGy was safe and wholesome and toxicological testing was no longer necessary

Question 9

what is the codex general standard of irradiated foods?

Answer 9

used for regulations of irradiated food for different countries

Question 10

in 1986, why did RDA issue a regulation for a max dose of irradiation?

Answer 10

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

Question 11

what is the USNRC?

Answer 11

united states nuclear regulation commission

Question 12

what is AECB? what is it now named?

Answer 12

atomic energy control board

now named nuclear safety commission

Question 13

what is dosimetry?

Answer 13

measurement of radiation dose

Question 14

what is a dosimeter?

Answer 14

instrument for measuring dose

Question 15

what is the role of dosimetry in food irradiation?

Answer 15

• 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

Question 16

what is considered a low or low dose?

Answer 16

low dose: 0.6 to 10kGy

high dose: 5 to 50 kGy

Question 17

in dosimeters, ceric ions are reduced to what?

Answer 17

cerous ions

Question 18

what is one of the most useful reference dosimeters?

Answer 18

Fricke (ferous feric)

Question 19

describe the Fricke ferous feric dosimeteter

Answer 19

• 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

Question 20

what are post harvest applications of radiation preservation?

Answer 20

• 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

Question 21

what are benefits of radiation preservation?

Answer 21

• low energy consumption
• environmental cleanliness
• potential to reduce use of fumigants and pesticides

Question 22

what are advantages of irradiation?

Answer 22

• killing microbial contaminants
• sterilizing or killing adult insects, larvae and eggs
• can be applied to fruits in a fresh state
• physical process
• high reliability

Question 23

what are effects of radiation on polysaccharides?

Answer 23

partly depolymerized cellulose, pectin and starch

Question 24

what are effects of radiation on proteins?

Answer 24

• they are less affected although reduction of disulfide bonds may lead to inactivation of active site and conformational changes in enzymes

Question 25

what are effects of radiation on nucleic acids

Answer 25

• NAs are main targets of free radicals generated by gamma rays

Question 26

what are the principal targets of gamma rays?

Answer 26

• nucleic acids and membrane lipids
• alteration in DNA
• alteration in membrane lipids

Question 27

how do gamma rays affect DNA

Answer 27

• affecting gene expression
• affects biosynthesis of some enzymes
• interferes with cell division

Question 28

how do gamma rays alter membrane lipids?

Answer 28

leads to perturbation of membrane functions and permeability

Question 29

as gamma ray energy increases, how does the relative contribution to ionization change? (compton effect)

Answer 29

increases, then decreases slowly

Question 30

as gamma ray energy increases, how does the relative contribution to ionization change? (for pair production)

Answer 30

increases slowly

Question 31

gamma rays interact mainly with what?

Answer 31

water molecules

Question 32

what does the interaction of gamma rays with water cause?

Answer 32

• 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

Question 33

in the ionization or radiolysis of water, what rxns take place?

Answer 33

1. H2O + E –> H2O* (excited water)
2. H2O + E –> H3O+ + e
3. H2O* –> OH. + H. (free radicals)
4. OH* + OH* –> H2O2 (H peroxide)