Transcript FOOD IRRADIATION - E-Course

ΠΑΝΕΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ
ΑΝΟΙΚΤΑ ΑΚΑΔΗΜΑΪΚΑ
ΜΑΘΗΜΑΤΑ
Προχωρημένα Μαθήματα
Επεξεργασίας και Συντήρησης
Τροφίμων
Συντήρηση με ακτινοβόληση (FOOD IRRADIATION)
Διδάσκοντες: Κ. Ακρίδα, Π. Δεμερτζής, Κ.
Ρηγανάκος, Ι. Σαββαΐδης
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FOOD IRRADIATION
 Ionizing radiation: takes the form of γ – rays from
isotopes or from x- rays and electrons.
 It is currently used in more than 35 countries.
Table 2. Applications of food irradiation
Application
Dose range
(kGy)
Sterilization
7-10
Up to 50
Sterilization of
packaging materials
10-25
Pathogen destruction
Salmonella species
2.5-5
3-10
Examples of foods
Herbs, spices
Long-term ambient storage
of meat
Frozen blocks, poultry, meat,
frozen shrimps, spices
Shigella species
Campylobacter species
Control of moulds
2-5
Extended storage of fresh
fruit
Notes
Outside the
permitted
dose
Table 2. Applications of food irradiation (continued)
Application
Dose range Examples of foods
(kGy)
Extension of chill life
from 5 days to 1 month
2-5
Inactivation or control
parasites (Trichinella
species, Taenia species)
0.1-6
Pork
Insect control, disinfestation
0.1-2
Fruit, grain, flour, cocoa
beans, dry fruits
Decontamination of food
ingredients
7-10
Dry food mixes
Inhibition of sprouting
0.1-0.2
Soft fruit, fresh fish and meat
at 0-4oC
Potatoes, onions, garlic
Notes
Experimental
Main advantages of irradiation:
(1) There is little or no heating of the food and therefore
minor change to sensory characteristics.
(2) Packaged and frozen foods may be treated.
(3) Fresh foods may be preserved in a single operation, and
without the use of chemical preservatives.
(4) Energy requirements are very low.
(5) Changes in nutritional value of foods are comparable
with other methods of food preservation.
(6) Processing is automatically controlled and has low
labour costs.
Main disadvantage:
*High capital cost of irradiation plant.
Other problems/disadvantages:
(1) loss of nutritional value.
(2) the possible development of resistance to radiation
in micro-organisms.
(3) inadequate analytical procedures for detecting
whether foods have been irradiated and
(4) public resistance due to fears of induced
radioactivity.
THEORY
 Summary of units used
Becqerel (Bq):
Half-life:
:
one unit of disintegration per second
the time taken for the radioactivity of a
sample to fall to half its initial value
Electron volt (eV):
energy of radiation (usually as
mega-electronvolts (MeV)
Grays (Gy):
absorbed dose (where 1 Gy is the
absorption of 1J of energy per kilogram
of food)
Previously rads (radiological units) were
used, where 1 rad=100 ergs/g=10-2 J kg-1
1 Gy therefore equals 100 rads.
γ – rays and electrons are exerting an ionizing ability (able to
break chemical bonds).
 Products of ionization: electrically charged (ions) or
neutral (free radical).
 Further reactions of ions and free radicals to cause changes in
an irradiated product (radiolysis). These reactions are
responsible for m/o, insects and parasites destruction.
 Water in fresh or high-moisture foods is ionized by
irradiation.
 Ionization of water and formation of radicals by irradiation
H2O  H2O+ + ee- + H2O  H2OH2O+
 H+ + OH·
H2O H· + OHIonization of water
H· + H·
 H2
or OH· + OH·  H2O2
or H· + OH·
 H2O
or H· + H2O
 H2 + OH·
or OH· + H2O2  H2O + HO2 ·
H· + O2  HO2 ·
Formation of radicals by irradiation
Radicals: extremely short lived (< 10-5 sec), but sufficient to
destroy bacterial cells.
 Fat-soluble components and essential fatty acids are lost
during irradiation (development of rancid off – flavors)
Therefore: some foods (e.g. dairy products) = unsuitable for
irradiation.
EQUIPMENT
 High – energy isotope source to produce γ – rays (60Co or
137Cs) or machine source to produce a high – energy electron
beam.
 Isotope source: cannot be switched off and is shielded within
a pool of water. It is raised only in operation (packaged food
is transported through the radiation field in a circular path).
 Isotope irradiation plant: It comprises (1) irradiation
chamber, (2) control room, (3) infeed conveyor, (4) outlet
conveyor, (5) raw food store, (6) irradiated product store, (7)
concrete shielding wall.
EFFECT ON MICROORGANISMS
 Injury/destruction of m/o by changing cell membrane
structure and affecting metabolic enzyme activity.
 More important effect: on DNA and RNA molecules in cell
nuclei.
 Rate of destruction: depends on the rate of ion production.
 Reduction in cell numbers: depends on the total dose of
radiation received.
Theoretically: a logarithmic reduction in m/o numbers with
increasing dose is expected. However, the destruction rate is
not always linear with dose ( some m/o can repair damaged
DNA or contain more than one DNA molecules).
 The rate of destruction varies with microbial species (figure 5)
Fig. 5. Microbial destruction by irradiation: curve A, Pseudomonas; curve B,
Salmonella; curve C, Bacillus cereus; curve D, Deinococcus radiodurans; curve E,
typical virus.
 D10 value (dose reducing m/o population to 10% of its initial
value): expresses the sensitivity of m/o to radiation.
 General rule: The smaller and simpler the organism the
higher the dose of radiation needed to destroy it.
 Viruses: very resistant, unlikely to be affected by dose
levels commercially used.
 Yeasts and molds: readily (at low doses) destroyed.
 Spore forming species: more resistant
 Food poisoning bacteria: less resistant and this is likely to
become one of the most important applications of food
irradiation.
The dose given to a food depends on:
(a) The resistance of the m/o present
(b) The objective of the treatment
 Combination of irradiation with heating is beneficial in
causing a greater reduction in m/o numbers than would be
achieved by either treatment alone. Also, enzymic spoilage
is not entirely prevented by irradiation.
 Two potential problems of irradiation are:
(1) that by destroying spoilage m/o and not destroying
pathogenic bacteria a valuable indicator of
wholesomeness is removed, and
(2) that the destruction of toxins-producing bacteria
after they have contaminated the food
with toxins is a health hazard.
WHOLESOMENESS OF IRRADIATED FOODS
The most important aspects of wholesomeness to be
considered:
(1) Can the process induce radioactivity?
(2) Can a safety program prevent exposure of
personnel to radioactivity during processing?
(3) Do the changes in surviving microflora create a
potential hazard?
(4) Does the process result in nutrient losses and/or
toxic product formation of public health
significance?
(5) Does the energy input by radiation result in
chemical reactions producing toxic or carcinogenic
compounds?
(1) Induced radioactivity
 Maximum recommended dose for foods: 15 kGy
 Average dose: < 10 kGy
At this dose: 60Co and 137Cs do not induce radioactivity in the
food. Machine sources of e and x-rays induce insignificant
levels of radioactivity (far below the acceptable dose).
(2) Radiolytic products
 Ions and radicals are capable of reacting with food
components to produce radiolytic products.
 Extend of radiolysis: depends on food type and radiation
dose
 However, no or little adverse effects have been found.
(3) Toxicity and Carcinogenicity
 According to existing data: no clear indication of acute or
chronic toxicity or carcinogenicity.
EFFECT OF FOOD PROCESSING AND
PRESERVATION METHODS ON THE
NUTRITIVE VALUE OF FOODS
1. BASIC PRINCIPLES
 Many unit operations, especially those that do not involve
heat, have little or no effect on the nutritional quality of
foods. Examples include mixing, cleaning, sorting, freeze
drying and pasteurization.
 Heat processing is a major cause of changes to nutritional
properties of foods.
 Heat also destroys some types of heat-labile vitamin (Fig.1),
reduces the biological value of proteins (owing to destruction
of amino acids or Maillard browning reactions) and promotes
lipid oxidation.
Fig. 1. Stability of vitamins in food
 Oxidation: is a second important cause of nutritional changes to
foods.
 It occurs when food is exposed to air (for example in size
reduction or hot-air drying) or as a result of the action of heat
or
oxidative enzymes (for example peroxidase or lipoxygenase).
 Main nutritional effects of oxidation:
(1) the degeneration of lipids to hydroperoxides and
subsequent reactions to form a wide variety of
carbonyl compounds, hydroxy compounds and short
chain fatty acids, and in frying oils to toxic compounds.
(2) destruction of oxygen-sensitive vitamins.
 The importance of nutrient losses during processing depends
on the nutritional value of a particular food in the diet.
 In industrialized countries, the majority of the population
achieve an adequate supply of nutrients from the mixture of
foods that is eaten. Losses due to processing of one
component of the diet are therefore insignificant to the longterm health of an individual.
 Variation in nutrient losses between cultivars or varieties can
exceed differences caused by alternative methods of
processing.
 Growth conditions, or handling and preparation procedures
prior to processing, also cause substantial variation in nutrient
loss.
2. EFFECT OF IRRADIATION ON NUTRITIVE
VALUE & SAFETY OF FOODS
 At commercial dose levels, ionizing radiation has little or no
effect on the digestibility of proteins or the composition of
essential amino acids.
 At higher dose levels, cleavage of the sulphydryl group from
sulphur amino acids in proteins causes changes in the aroma
and taste of foods.
 Carbohydrates are hydrolyzed and oxidized to simpler
compounds and, depending on the dose received, may
become depolymerized and more susceptible to enzymic
hydrolysis, without any reduction in nutritional value.
Effect on lipids: similar to that of autoxidation – Foods
having high lipid concentrations are generally unsuitable for
irradiation.
 Water soluble vitamins vary in their sensitivity to
irradiation.
 The extent of vitamin loss also depends on the dose
received and the type and physical state of food under
investigation.
 The effects on thiamine in meat and poultry are likewise
inconsistent but other vitamins of the B group are largely
unaffected.
 Fat soluble vitamins vary in their susceptibility to radiation.
Vitamins D and K are largely unaffected whereas vitamins A
and E undergo some losses, which vary according to the type
of food examined.
 In conclusion: At commercial dose levels, irradiation causes
no greater damage to nutritional quality than other
preservation operations used in food processing.
RECENT CONCERNS ABOUT THE SAFETY OF
IRRADIATED FOODS
• - Recently, many in the Scientific Community are opposed to irradiation.
• They allege that:
• (a) γ-rays can kill harmful bacteria in food, but one big problem is they kill
the helpful microflora, too.
• (b) Food irradiation increases the levels of mutagens and carcinogens in
the food. As a consequence, in two or five decades in the future, the
incidence of cancer will increase in direct proportion to the amounts of
irradiated food consumed.
• (c) Irradiation causes a host of unnatural and sometimes unidentifiable
chemicals to be formed within the irradiated food. The number, kind, and
permanence of these depend on the food itself and the irradiation dose.
• (d) Mutagenic doses of formaldehyde are formed during irradiation of
carbohydrate.
• A new class of chemicals can be formed during food
Irradiation. These chemicals, called cyclobutanones, do not
occur naturally anywhere on Earth. They recently were found to cause
genetic damage in rats, and genetic and cellular damage in human and rat
cells.
• This class of chemicals can be formed in many irradiated foods including
beef, pork, chicken, lamb, eggs, tropical fruits (mangoes and papayas).
• Moreover:
•
From a nutritional perspective, exposing food to irradiation depletes
vitamins, often significantly. Especially vulnerable are A, the B-complex, C,
E, and β-carotene.
• From a chemical perspective, irradiation blows apart bonds, resulting
in the formation of hundreds of new compounds, some of them being
known or suspected to cause cancer or birth defects.
• Examples of these compounds are:
•
•
•
•
•
Benzene,
Ethanol,
Hexane,
Methyl ethyl ketone,
Toluene.
• From an aesthetic perspective, irradiation can destroy the
flavor, odor and texture of food.
• - Another concern is that irradiation will eventually be used
to mask filthy slaughtering and food processing practices.
• Substandard food could be “treated” with high-dose radiation
in unlicensed and dirty facilities. This fact could jeopardize the
quality and safety of food sold to the consumers.
Τέλος Ενότητας
Χρηματοδότηση
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εκπαιδευτικού έργου του διδάσκοντα.
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«Εκπαίδευση και Δια Βίου Μάθηση» και συγχρηματοδοτείται από την
Ευρωπαϊκή Ένωση (Ευρωπαϊκό Κοινωνικό Ταμείο) και από εθνικούς
πόρους.
Σημειώματα
Σημείωμα Ιστορικού Εκδόσεων
Έργου
Το παρόν έργο αποτελεί την έκδοση 1.0.
Έχουν προηγηθεί οι κάτωθι εκδόσεις:
•Έκδοση 1.0 διαθέσιμη εδώ.
http://ecourse.uoi.gr/course/view.php?id=1072.
Σημείωμα Αναφοράς
Copyright Πανεπιστήμιο Ιωαννίνων, Διδάσκοντες: Κ.
Ακρίδα, Π. Δεμερτζής, Κ. Ρηγανάκος, Ι. Σαββαΐδης.
«Προχωρημένα Μαθήματα Επεξεργασίας και
Συντήρησης Τροφίμων. Συντήρηση με ακτινοβόληση
(FOOD IRRADIATION)». Έκδοση: 1.0. Ιωάννινα 2014.
Διαθέσιμο από τη δικτυακή διεύθυνση:
http://ecourse.uoi.gr/course/view.php?id=1072.
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χρήσης Creative Commons Αναφορά Δημιουργού Παρόμοια Διανομή, Διεθνής Έκδοση 4.0 [1] ή
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