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FOSC302 > UV and ionising radiation > Flashcards

UV and ionising radiation Flashcards

1
Q

what is the intensity (I) of UV radiation expressed as

A

irradiance or intensity flux (Wcm-2)

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2
Q

what is fluence (F)

A

a function of intensity and time and can be expressed as radiant exposure ( W s cm-2) or (J m-2)

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3
Q

freq (Hz) of UV

A

(6 x 10^16) - (7.5 x 10^16)

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4
Q

energy of UV (eV)

A

3.1-247.8

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5
Q

the way electromagnetic radiation is transmitted

A

discrete packets aka quanta

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6
Q

what range is UV radiation most lethal to microorganisms (peak in brackets)

A

240-280 nm (260-265)

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7
Q

optimal germicidal radiation

A

253.7 nm

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8
Q

why 253.7 nm

A

it is where DNA is most effectively damaged

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9
Q

primary lethal effect of UV

A

due to its absorption by the DNA of the nucleus

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10
Q

other biological effects of UV

A

induces changes in proteins (functional and structural cell content)
limited effect on cell function/integrity as cells have back up mechanisms

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11
Q

why does DNA have such high absorbance

A

pyrimidine and purine bases

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12
Q

what does absorption of UV promote in the DNA bases

A

chemical reactions

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13
Q

what do the products of the chemical reactions in the bases do

A

interfere with DNA replication and transcription

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14
Q

what are the products of DNA base reactions and UV called

A

photoproducts

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15
Q

what do most photoproducts contain

A

pyrimidine bases including dimmers or other pyrimidine adducts and hydrates

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16
Q

what is the resistance of a microorganism to UV determined by

A

ability to repair damage

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17
Q

name of microorganism that can synthesize protective pigments

A

micrococci

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18
Q

least to most resistant microorganisms?

A

gram neg< gram positive=yeasts< bacterial spores< mould spores&laquo_space;viruses

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19
Q

inactivation follows ___-_____ kinetics

A

log linear

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20
Q

impact of UV is effected by

A

species
growth conditions
growth phase
composition of suspension medium
cell density
UV source and specific spectral output

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21
Q

sources of UV radiation

A

solar
short wave UV lights
mercury lamps designed to produce energy in the germicidal range (264 nm)

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22
Q

short wavelength (UVC)

A

200-280nm

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23
Q

medium wavelength (UVB)

A

280-320nm

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24
Q

long wavelength (UVA)

A

320-400nm

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25
Q

long wavelength (UVA)

A

320-400nm

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26
Q

why does UV have limtied effectiveness

A

incident radiation is readily absorbed by the medium components and has very low penetration

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27
Q

most successful application of UV disinfection of liquids

A

sterilise portable water
depuration of shellfish

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28
Q

what may be an option to sterilise opaque liquids

A

using turbulent flow

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29
Q

application of UV in air

A

control of mould spores in bakeries
limit spread of micro-organisms through a building (install UV tubes in vent ducts)

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30
Q

application of UV on surfaces

A

packaging materials
process benches
meat lockers

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31
Q

adverse effects of UV

A

process workers: must be protected due to reddening of the skin/cancers and eye complaints
Foods: nutritional degradation especially vit C and B (does promote vit D tho), can also accelerate development of rancidity unless controlled by a layer of N

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32
Q

basis of ionising radiation

A

very effectively inhibits DNA synthesis by impairing cell division and reproduction
-at the right dose this does not impact food

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33
Q

low dose level purpose

A

kill parasites, insects and larvae
inhibit sprouting
slow ripening

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34
Q

examples of low dose

A

trichinae in pork
garlic/potato sprouting

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35
Q

low dose kGy

A

up to 1

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36
Q

medium dose kGy

A

1-10kGy

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37
Q

purpose of medium dose

A

pasteurization to eliminate spoilage organisms and foodborne illness-causing microbes

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38
Q

examples of medium dose

A

strawberries and grapes
fresh or frozen seafood

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39
Q

high dose kGy

A

10-50kGy

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40
Q

purpose of high dose kGy

A

sterilise food for immuno-compromised people
decontaminate food additives and ingredients

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41
Q

examples of high dose

A

pathogen free hospital food
spices, enzyme preperation, gums and aromatic substances

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42
Q

at what kGy are spices treated at

A

10kGy

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43
Q

three types of ionising radiation used in food

A

high energy electrons
x -rays
gamma rays

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44
Q

max energies of high energy electrons

A

10 MeV

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45
Q

which types of ionising radiation use high energy electromagnetic radiation with energies up to 5 MeV

A

x-ray and gamma rays

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46
Q

how are these rays distinguished from other forms of radiation

A

ionising ability: they can break chemical bonds when absorbed by materials

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47
Q

what are the products of ionisation

A

electrically charged ions or neutral (free radicals)

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48
Q

form and source of high energy electrons

A

beta particles produced by radioactive decay or machine-generated

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49
Q

penetration of high energy electrons

A

2.5cm of food

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50
Q

why are high energy electrons less penetrating than electromagnetic radiation

A

mass and charge as they are particles rather than em radiation

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51
Q

how are x-ray generated

A

bombardment of heavy metal targets with high velocity electrons (cathode rays) within an evacuated tube

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52
Q

the penetrating power of X-rays

A

25cm

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53
Q

how are gamma rays produced

A

decay of radioactive isotopes

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54
Q

most common radioactive isotope

A

cobalt 60 and cesium 137

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55
Q

penetration of gamma rays

A

20cm

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56
Q

which radiation has the best penetration

A

X-rays

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57
Q

advantages to gamma radiation

A

-relatively inexpensive

58
Q

what are cobalt 60 and cesium 137

A

by-products of atomic fusion

59
Q

describe the application of gamma rays

A

the radioactive material is placed on a movable platform underwater followed by the material wanting to be irradiated. All personal must leave and the source is then raised to treat the food

60
Q

disadvantages to gamma radiation

A

rays are emitted in all directions
no on or off button
short half life of Cobalt 60, periodically change the source to maintain given radiation

61
Q

half life of cobalt 60 and cesium 137

A

60: 5.27 years
137: 30 years

62
Q

describe the direction of ray emission for the three radiation techniques

A

electrons: pass straight through, directional
X-rays: scattered but still in the right direction
Gamma: emmited in all directions

63
Q

advantages of an electron beam/accelerated electrons

A

allow for direct application
efficiently converted to X-rays
current and energy can be changed to suit the product
can be turned on or off
rays can be directed

64
Q

describe the principle of an electron beam in relation to a TV

A

rather than the electrons being widely dispersed and hitting a fluorescent screen, they are concentrated and accelerated to 99% of the speed of light

65
Q

MeV that electrons can be accelerated to

A

10MeV

66
Q

describe the use of a converter plate (Pb) to generate X-rays

A

lead is placed under the scanning horn and converted to X-rays at a 5MeV energy level to allow for deep penetrations

67
Q

why is using a converter plate expensive

A

low energy conversion efficiency of electrons to X-rays

68
Q

technical features of rhodotron

A

up to 10MeV energy: great processing variability with deep penetration
high electrical efficency 10-200kW beam power: low operating cost
continuous wave: best production matching capability, can X-ray convert, precision dosing, unrestricted line combinations
narrow energy spectrum: the ability to customize scan configurations
simple design: reliable and stable

69
Q

how is the energy of radiation expressed

A

rad or Grays(newer)

70
Q

how is a dose of 1 rad obtained

A

0.01 joule is absorbed per kg of material

71
Q

conversion of jou to gray to rad

A

1 joule = 1 gray = 100rads

72
Q

what unit of gray is used for conveience

A

kilo Gray (kGY)

73
Q

unit used for the nergy gained by an electron moving throgh 1 volt

A

electron volt (eV)

74
Q

what is MeV equivalent to

A

1 million electron volts

75
Q

what hapens to water in foods after radiation

A

becomes ionised

76
Q

what happens to the electrons in the ionised water molecules

A

expelled from them

77
Q

are products of inoisation electrically charged

A

they are both charged (ions) and uncharged (free radicals)

78
Q

what happens to the ionised products post radiation

A

they recobine to form H, H2O2, or radicals H-, OH-, HO2-

79
Q

what is the effect of ionising radation on cells

A

directly: interacting with key molecules within the microbial cell
indirectly: through inhibitory effects of free radicals

80
Q

what is the most important free radical and what does it do

A

OH- damages DNA (90%)
-it is formed in the hydration layer around the DNA

81
Q

damage that mainly occurs in living cells

A

indirect

82
Q

mechanism of damage to DNA

A

chemical damage to purine and pyrimidine bases
hydrogen abstraction from deoxyribose sugars followed by Beta-elimnation of phosphate

83
Q

what happens to the phosphodiester backbone of DNA after hydrogen abstraction occurs

A

it breaks in one or two DNA strands

84
Q

what does it take for a double strand DNA cleave

A

5-10% of what is required for a single strand break

85
Q

what does the resistance of an organism to ionising radiation depending on

A

ability to repair damage caused

86
Q

are single strand breaks affective

A

not really most micro-organisms can repair them

87
Q

can micro-organisms repair double-stranded breaks

A

sensitive ones cannot like e.Coli
but highly resistant like Deinococcus spp can

88
Q

describe the rate of death graph

A

logarithmic with the curves often exhibiting a should or tail

89
Q

which species often have a more pronounced curve and why

A

bacteria because they have more efficient repair mechanisms

90
Q

where are D-values derived from

A

the linear portion of the curve

91
Q

most resistant micro-organism

A

virus

92
Q

most to least resistant species

A

viruse> yeast> spores>moulds=gram positive bacteria> gram negative

93
Q

when is bacteria most resistant to radiaition

A

lag phase

94
Q

when is bacteria most sensitive

A

log phase

95
Q

how does the composition of food affect microbial reisstance

A

protein has a protective effect
higher the competition for the free radicals to form the better protection

96
Q

how does oxygen concentration affect resistance

A

RADIATION IS GREATER IN ABSCENCE OF o2

97
Q

how does water activity affect resistance

A

drier and frozen cells have more resistance due to the decreased levels of free radicals from water

98
Q

how does temperature affect resistance

A

sub-lethal temps around 45C enhances lethal effects of radiation in vegetative cells

99
Q

what is radappertisation

A

sterilisation/commercial sterility

100
Q

is radappertisation likely

A

unlikey in near future due to extremely high required doses

101
Q

radappertisation values for food

A

bacon: 23kGy
beef:47 kGy
chicken: 45kGy
pork 51kGy

102
Q

what does radation at extremely high levels cause in food

A

colour changes and prouction of off-odours

103
Q

what kGy does WHO state as being “unconditionally safe for human consumption”

A

7kGy

104
Q

what kGy does FAO/WHO allow

A

up to 10kGy

105
Q

uses of food irridiation

A

pasteurisation
-reduction of pathogens other than viruses
-reduce spoilage micorobes
-extend shelf life
inhibition of sprouting
disinfestation
contorl of parasites
contorl of ripening
control of micro-organsims

106
Q

typical level required for reduction in pathogens during pastuerisation

A

2.5 (salmonella in poultry) - 10 kGy

107
Q

typical level required for the reduction of spoilage microbes

A

0.75-2.5 kGy

108
Q

hoow much cna it extend shelf life by

A

2-6 fold

109
Q

dose inhibit sprouting

A

0.1-0.2

110
Q

what are the results of inhibiting sprouting

A

increeasesd shelf life
reduction in malting losses

111
Q

typical level required for disinfestation

A

0.2-0.8

112
Q

results of radiation for disinfestation

A

redcued losses
increased export potential
avoids use of pesticides

113
Q

application level for contorl of prarsites

A

0.3-0.5 kGy

114
Q

results of using radiation to control parasites

A

prevention of growth and reproduction of parasites along with death
enhanced food safety
meet export requirements

115
Q

dose level to control micro-organsisms

A

3-10kGy

116
Q

results of radiation to contorl micro-organsisms

A

reduced contamination
enhance food safety
increased shelf life

117
Q

effect of irradiation on food quality

A

production of irridiation odours
degradation in pectin and cellulose = softening (only high doses)
proteins adn N compounds are most sensitive so NH, hydrogen, CO2 and carbonyls may be formed

118
Q

what are the most sensiitve amino acids

A

methionine, cysteine, histidine, arginine and tyrosine

119
Q

what does vitamin loss depend on

A

dose
type of food
physical state

120
Q

grain example for vitamin loss

A

0.1 (disinfestation) no loss
0.11 (inhibition of sprouting) 28% loss

121
Q

summary of nutritional wuality damage of irradation

A

no greater damage than other preservation methods

122
Q

how does reducing temp minimise irradiation side effects

A

immobilisatoin of free radicals

123
Q

how does reducing oxygen tension minimise irradiation side effects

A

reduction in number of oxidative free radicals

124
Q

how does addition of free radical scaavengers minimise irradiation side effects

A

competition for free rasicals by scavengers

125
Q

how does concurrent radiation distillation minimize irradiation side effects

A

removal of volatile off flavours/odour precursors

126
Q

how does reducing the dose minimise irradiation side effects

A

lessening the effect

127
Q

what could irridiation in packaging cause the production of

A

low molecular weight hydrocarbons, halogenated polymers which can potentially cause a taint in food

128
Q

effect of radiation above maximum dose on PVC

A

browning, evolution of HCl

129
Q

effect of radiation above maximum dose on paper and board

A

loss of mechanical strength

130
Q

effect of radiation above maximum dose on polypropylene

A

becomes brittle

131
Q

effect of radiation above maximum dose on glass

A

browning

132
Q

advantages to food irradiation

A

more precisely controlled than heating (instant, deep and uniform penetration)

133
Q

lethal dose of ionising radiation for enzymes

A

> 100kGy

134
Q

lethal dose of ionising radiation for viruses

A

30-50 kGy

135
Q

lethal dose of ionising radiation for bacterial spores

A

10-30 kGy

136
Q

lethal dose of ionising radiation for funghi

A

1.5-10 kGy

137
Q

lethal dose of ionising radiation for bacteria

A

1-5 kGy

138
Q

lethal dose of ionising radiation for insects

A

0.25-1

139
Q

lethal dose of ionising radiation for humans

A

0.006-0.01 kGy

140
Q

disadvantages to food irradiation

A

large capital cost
extensive consumer resistance and mistrust
requirement for labeling
not very against viruses or spores
concern it will “hide” poor manufacturing practices
not all foods can be treated
require stringent safety measures in facilities

FOSC302 (14 decks)

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