UV and ionising radiation Flashcards
(140 cards)
1
Q
what is the intensity (I) of UV radiation expressed as
A
irradiance or intensity flux (Wcm-2)
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)
3
Q
freq (Hz) of UV
A
(6 x 10^16) - (7.5 x 10^16)
4
Q
energy of UV (eV)
A
3.1-247.8
5
Q
the way electromagnetic radiation is transmitted
A
discrete packets aka quanta
6
Q
what range is UV radiation most lethal to microorganisms (peak in brackets)
A
240-280 nm (260-265)
7
Q
optimal germicidal radiation
A
253.7 nm
8
Q
why 253.7 nm
A
it is where DNA is most effectively damaged
9
Q
primary lethal effect of UV
A
due to its absorption by the DNA of the nucleus
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
11
Q
why does DNA have such high absorbance
A
pyrimidine and purine bases
12
Q
what does absorption of UV promote in the DNA bases
A
chemical reactions
13
Q
what do the products of the chemical reactions in the bases do
A
interfere with DNA replication and transcription
14
Q
what are the products of DNA base reactions and UV called
A
photoproducts
15
Q
what do most photoproducts contain
A
pyrimidine bases including dimmers or other pyrimidine adducts and hydrates
16
Q
what is the resistance of a microorganism to UV determined by
A
ability to repair damage
17
Q
name of microorganism that can synthesize protective pigments
A
micrococci
18
Q
least to most resistant microorganisms?
A
gram neg< gram positive=yeasts< bacterial spores< mould spores«_space;viruses
19
Q
inactivation follows ___-_____ kinetics
A
log linear
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
21
Q
sources of UV radiation
A
solar
short wave UV lights
mercury lamps designed to produce energy in the germicidal range (264 nm)
22
Q
short wavelength (UVC)
A
200-280nm
23
Q
medium wavelength (UVB)
A
280-320nm
24
Q
long wavelength (UVA)
A
320-400nm
25
long wavelength (UVA)
320-400nm
26
why does UV have limtied effectiveness
incident radiation is readily absorbed by the medium components and has very low penetration
27
most successful application of UV disinfection of liquids
sterilise portable water
depuration of shellfish
28
what may be an option to sterilise opaque liquids
using turbulent flow
29
application of UV in air
control of mould spores in bakeries
limit spread of micro-organisms through a building (install UV tubes in vent ducts)
30
application of UV on surfaces
packaging materials
process benches
meat lockers
31
adverse effects of UV
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
32
basis of ionising radiation
very effectively inhibits DNA synthesis by impairing cell division and reproduction
-at the right dose this does not impact food
33
low dose level purpose
kill parasites, insects and larvae
inhibit sprouting
slow ripening
34
examples of low dose
trichinae in pork
garlic/potato sprouting
35
low dose kGy
up to 1
36
medium dose kGy
1-10kGy
37
purpose of medium dose
pasteurization to eliminate spoilage organisms and foodborne illness-causing microbes
38
examples of medium dose
strawberries and grapes
fresh or frozen seafood
39
high dose kGy
10-50kGy
40
purpose of high dose kGy
sterilise food for immuno-compromised people
decontaminate food additives and ingredients
41
examples of high dose
pathogen free hospital food
spices, enzyme preperation, gums and aromatic substances
42
at what kGy are spices treated at
10kGy
43
three types of ionising radiation used in food
high energy electrons
x -rays
gamma rays
44
max energies of high energy electrons
10 MeV
45
which types of ionising radiation use high energy electromagnetic radiation with energies up to 5 MeV
x-ray and gamma rays
46
how are these rays distinguished from other forms of radiation
ionising ability: they can break chemical bonds when absorbed by materials
47
what are the products of ionisation
electrically charged ions or neutral (free radicals)
48
form and source of high energy electrons
beta particles produced by radioactive decay or machine-generated
49
penetration of high energy electrons
2.5cm of food
50
why are high energy electrons less penetrating than electromagnetic radiation
mass and charge as they are particles rather than em radiation
51
how are x-ray generated
bombardment of heavy metal targets with high velocity electrons (cathode rays) within an evacuated tube
52
the penetrating power of X-rays
25cm
53
how are gamma rays produced
decay of radioactive isotopes
54
most common radioactive isotope
cobalt 60 and cesium 137
55
penetration of gamma rays
20cm
56
which radiation has the best penetration
X-rays
57
advantages to gamma radiation
-relatively inexpensive
58
what are cobalt 60 and cesium 137
by-products of atomic fusion
59
describe the application of gamma rays
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
disadvantages to gamma radiation
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
half life of cobalt 60 and cesium 137
60: 5.27 years
137: 30 years
62
describe the direction of ray emission for the three radiation techniques
electrons: pass straight through, directional
X-rays: scattered but still in the right direction
Gamma: emmited in all directions
63
advantages of an electron beam/accelerated electrons
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
describe the principle of an electron beam in relation to a TV
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
MeV that electrons can be accelerated to
10MeV
66
describe the use of a converter plate (Pb) to generate X-rays
lead is placed under the scanning horn and converted to X-rays at a 5MeV energy level to allow for deep penetrations
67
why is using a converter plate expensive
low energy conversion efficiency of electrons to X-rays
68
technical features of rhodotron
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
how is the energy of radiation expressed
rad or Grays(newer)
70
how is a dose of 1 rad obtained
0.01 joule is absorbed per kg of material
71
conversion of jou to gray to rad
1 joule = 1 gray = 100rads
72
what unit of gray is used for conveience
kilo Gray (kGY)
73
unit used for the nergy gained by an electron moving throgh 1 volt
electron volt (eV)
74
what is MeV equivalent to
1 million electron volts
75
what hapens to water in foods after radiation
becomes ionised
76
what happens to the electrons in the ionised water molecules
expelled from them
77
are products of inoisation electrically charged
they are both charged (ions) and uncharged (free radicals)
78
what happens to the ionised products post radiation
they recobine to form H, H2O2, or radicals H-, OH-, HO2-
79
what is the effect of ionising radation on cells
directly: interacting with key molecules within the microbial cell
indirectly: through inhibitory effects of free radicals
80
what is the most important free radical and what does it do
OH- damages DNA (90%)
-it is formed in the hydration layer around the DNA
81
damage that mainly occurs in living cells
indirect
82
mechanism of damage to DNA
chemical damage to purine and pyrimidine bases
hydrogen abstraction from deoxyribose sugars followed by Beta-elimnation of phosphate
83
what happens to the phosphodiester backbone of DNA after hydrogen abstraction occurs
it breaks in one or two DNA strands
84
what does it take for a double strand DNA cleave
5-10% of what is required for a single strand break
85
what does the resistance of an organism to ionising radiation depending on
ability to repair damage caused
86
are single strand breaks affective
not really most micro-organisms can repair them
87
can micro-organisms repair double-stranded breaks
sensitive ones cannot like e.Coli
but highly resistant like Deinococcus spp can
88
describe the rate of death graph
logarithmic with the curves often exhibiting a should or tail
89
which species often have a more pronounced curve and why
bacteria because they have more efficient repair mechanisms
90
where are D-values derived from
the linear portion of the curve
91
most resistant micro-organism
virus
92
most to least resistant species
viruse> yeast> spores>moulds=gram positive bacteria> gram negative
93
when is bacteria most resistant to radiaition
lag phase
94
when is bacteria most sensitive
log phase
95
how does the composition of food affect microbial reisstance
protein has a protective effect
higher the competition for the free radicals to form the better protection
96
how does oxygen concentration affect resistance
RADIATION IS GREATER IN ABSCENCE OF o2
97
how does water activity affect resistance
drier and frozen cells have more resistance due to the decreased levels of free radicals from water
98
how does temperature affect resistance
sub-lethal temps around 45C enhances lethal effects of radiation in vegetative cells
99
what is radappertisation
sterilisation/commercial sterility
100
is radappertisation likely
unlikey in near future due to extremely high required doses
101
radappertisation values for food
bacon: 23kGy
beef:47 kGy
chicken: 45kGy
pork 51kGy
102
what does radation at extremely high levels cause in food
colour changes and prouction of off-odours
103
what kGy does WHO state as being "unconditionally safe for human consumption"
7kGy
104
what kGy does FAO/WHO allow
up to 10kGy
105
uses of food irridiation
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
typical level required for reduction in pathogens during pastuerisation
2.5 (salmonella in poultry) - 10 kGy
107
typical level required for the reduction of spoilage microbes
0.75-2.5 kGy
108
hoow much cna it extend shelf life by
2-6 fold
109
dose inhibit sprouting
0.1-0.2
110
what are the results of inhibiting sprouting
increeasesd shelf life
reduction in malting losses
111
typical level required for disinfestation
0.2-0.8
112
results of radiation for disinfestation
redcued losses
increased export potential
avoids use of pesticides
113
application level for contorl of prarsites
0.3-0.5 kGy
114
results of using radiation to control parasites
prevention of growth and reproduction of parasites along with death
enhanced food safety
meet export requirements
115
dose level to control micro-organsisms
3-10kGy
116
results of radiation to contorl micro-organsisms
reduced contamination
enhance food safety
increased shelf life
117
effect of irradiation on food quality
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
what are the most sensiitve amino acids
methionine, cysteine, histidine, arginine and tyrosine
119
what does vitamin loss depend on
dose
type of food
physical state
120
grain example for vitamin loss
0.1 (disinfestation) no loss
0.11 (inhibition of sprouting) 28% loss
121
summary of nutritional wuality damage of irradation
no greater damage than other preservation methods
122
how does reducing temp minimise irradiation side effects
immobilisatoin of free radicals
123
how does reducing oxygen tension minimise irradiation side effects
reduction in number of oxidative free radicals
124
how does addition of free radical scaavengers minimise irradiation side effects
competition for free rasicals by scavengers
125
how does concurrent radiation distillation minimize irradiation side effects
removal of volatile off flavours/odour precursors
126
how does reducing the dose minimise irradiation side effects
lessening the effect
127
what could irridiation in packaging cause the production of
low molecular weight hydrocarbons, halogenated polymers which can potentially cause a taint in food
128
effect of radiation above maximum dose on PVC
browning, evolution of HCl
129
effect of radiation above maximum dose on paper and board
loss of mechanical strength
130
effect of radiation above maximum dose on polypropylene
becomes brittle
131
effect of radiation above maximum dose on glass
browning
132
advantages to food irradiation
more precisely controlled than heating (instant, deep and uniform penetration)
133
lethal dose of ionising radiation for enzymes
>100kGy
134
lethal dose of ionising radiation for viruses
30-50 kGy
135
lethal dose of ionising radiation for bacterial spores
10-30 kGy
136
lethal dose of ionising radiation for funghi
1.5-10 kGy
137
lethal dose of ionising radiation for bacteria
1-5 kGy
138
lethal dose of ionising radiation for insects
0.25-1
139
lethal dose of ionising radiation for humans
0.006-0.01 kGy
140
disadvantages to food irradiation
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
