Changes during Irradiation

1. CHEMICAL,NUTRITIONL
& MICROBIOLOGICL
CHANGES IN
IRRADIATED FOOD
JIKKY JAYAKUMAR
2015604104

2. SOURCE OF
RADIATION

3. Types of radiation
• Its referred as ionizing radiations because their energy is high enough to
dislodge electrons from atoms and molecules and to convert them to
electrically-charged particles called ions.
• Gamma rays and X-rays
• widely used for the irradiation of food by gamma rays is cobalt-60.
• Cesium-137 is the only other gamma rays suitable for industrial
processing of materials.
• X-ray machines having a maximum energy of five million electron volts
(MeV)

4. Radiation dose
 Radiation dose is the quantity of radiation energy absorbed by the food
as it passes through the radiation field during processing.
 It is measured using a unit called the Gray(Gy)
 International health and safety authorities have endorsed the safety of
irradiation for all foods up to a dose level of 10,000 Gy (10 kGy)
 low doses (<1kGy)- delay ripening, control insects and parasites
 Medium doses (1-7kGy)- reduction of food borne pathogens
 High doses (>25kGy) - sterilization

5.  1 Gy is equal to the transfer of 1 joule of energy per
kilogram of material (food).
 This change is proportional to dose and dose rate, and it
can be calibrated to a recognized dose standard.
 Dosimeters are used to record dose.

6. Effects of ionising radiation on
food
 The composition of food and its physical state (frozen or
fresh, solid, liquid or powder) also influence the extent of
the reactions induced by the radiation treatment
 absorbed dose, dose rate and facility type, presence or
absence of oxygen and temperature.

7. Generation of radiolytic products
 Chemical changes can occur via primary radiolysis effects
that result because of direct absorption of energy by the
irradiated food, and also by secondary indirect effects.
 the high reactivity of the free radicals and excited
molecular ions produced form very reactive
intermediates.
 leading to stable chemicalproducts, often referred toas
radiolytic products.

8.  the gamma irradiation of aerated water
 H2O → H2O++ e-
 H2O+ → H++ HO
 The chemical yield of both intermediate (reactive) and
final (stable) radiolytic products is often expressed using
a convenient unit of the G-value.
 The G value for the hydroxyl radical is 2.8.
 when foods are irradiated in air the G-value will be
different

9.  If the ionizing radiation initiates a chain reaction (e.g.,
autoxidation) then the chemical yield of the primary
irradiation product (leading in this case to lipid peroxyl
radicals) can be multiplied by the chain-length
 chemical classes such as hydrocarbons, furans,
alkylcyclobutanones, cholesterol oxides and aldehydes

10. Effects on food constituents
 Proteins
 protein structure (globular, fibrous), state (native or
denatured), physical status (in solution, solid, frozen),
amino acid composition.
 Major changes consist of dissociation, aggregation, cross-
linking and oxidation.
 gamma irradiation of hazelnuts at 10 kGy induced
aggregation and denaturation of proteins resulting in
moderate effects on the protein structure (Dogan et al.,
2007).

11.  monomeric enzymes causing autolysis/hydrolysis can not
be inactivated by irradiation, needing other treatments
(i.e., heating) to be inactivated (Delincée, 1983a).
 The main low molecular radiolytic products resulting from
peptide irradiation consist of compounds such as
ammonia, keto acids, amide-like products and diamino
acids (Delincée, 1983a).
 Aromatic and Sulphur containing amino acids are most
susceptible to irradiation.

12. lipids
Factors:
 lipid concentration,
 physical status (liquid or solid),
unsaturamonounsaturated fatty acids (MUFA) and
polyunsaturated fatty acids (PUFA)),
 presence of antioxidants, environmental conditions (light,
heat,oxygen, moisture, pH),
 the irradiation treatment, type of storage (vacuum,
modified atmosphere, etc.)
 storage conditions (time, temperature, light, etc.) tion
profile

13.  Lipid oxidation due larger fat content and high
unsaturated fatty acids so formation of free radicals
 using low temperatures and
 reducing the presence of oxygen
 use of antioxidants
 use of natural antioxidants like oregano and rosemary
extracts in beef burger subjected to E-beam
with doses up to 7 kGy and stored frozen stored for
to90 days, showed a great capacity to reduce lipid
oxidation (da Trindade et al., 2009).

14. Carbohydrates
 application of gamma-irradiation up to 6.2 kGy/h to
starches induce the formation of aldehydes such as
malonaldehyde, formaldehyde, and acetaldehyde, formic
acid and hydrogen peroxide as main radiolytic products

15. Vitamins
 Water soluble vitamins have different sensitivities to
irradiation. .
 Thiamine is the most sensitive and significant losses can
occur in meats
 Riboflavin, vitamin B6, vitamin B12and niacin have been
reported as fairly stable to irradiation (Diehl, 1991); in
absence of oxygen
 Fat soluble vitamins have different sensitivities to
irradiation and have been shown to decrease in the
following order: Vitamin E > β-carotene > vitamin A >
vitamin D > vitamin K (Diehl, 1995).

16. Microbiological changes
 Direct ionization of nucleic acids
 Lesions produced in genetic material
 Single stranded breaks are repairable (may cause mutation)
 double stranded breaks are leathal
Iowa State University

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