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Irradiation and High Pressure Processing

Covers food irradiation and high pressure

Richard Marshall

on 17 January 2017

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Transcript of Irradiation and High Pressure Processing

Irradiation and High Pressure Processing
Uses ionising radiation:
Gamma rays, from Co and Cs
Electron beam
Food Irradiation
What are these?
60 137
Gamma radiation, x-radiation
High energy electromagnetic radiation - photons

Gamma rays from unstable isotopes - radioactive
X-rays generated by electrical discharge in vacuum

Electron beam
Electrons stripped off cathode by electric current, accelerated towards positively charged target but pass through to hit external object
How do they work?
Energy transferred to vulnerable components in material (foods, cells)
Causes ionisation, breaking of nucleic acids, double bonds, rings etc
Disrupts cell function, kills
Free radicals generated from water
These cause damage to the sensitive molecules & structures
Food irradiation permitted around the world:
Radiation doses
'gray' after Louis Harold Gray, 1905-1965
One gray is absorbtion of one joule of radiation energy by one kg of matter

1 Gy = 1 J/kg (3.6 x 10 kJ = 1 kWh)

Food irradiated in kGy
i.e. 1 kGy = 1 kJ/kg
= ~ 2.8 x 10 kWh/kg

Effectiveness of irradiation
Highly effective
Can reduce contamination to safe levels
Causes few other changes in many foods
Probably causes fewer potentially harmful products than heating/cooking
Current usage of food irradiation in UK
Wide range are legally permitted
But only herbs & spices licensed
Problem with these is they are often contaminated
Heat damages characteristics
Irradiation can make them safe without such changes
Most herbs & spices are not treated this way
Dose rates
Nutritional effects
Macronutrients - fats, proteins, carbohydrates
generally no effect
BUT foods high in unsaturated fats may turn rancid

some loss of vitamins
similar to heat treatments

Taste, flavour, appearance
no changes
Irradiation of fruits & vegetables
Generally, no need to sterilise
But serious problems with infestation - post-harvest losses
Fruits imported from around the world
May contain pests etc
Also, fruits can over ripen
Irradiation delays ripening
Prevents sprouting in potatoes, tubers
Herbs, spices - air dried so potential faecal contamination from birds, rodents
Minced meat may be highly contaminated
Especially E. coli O157:H7 - deadly!
High Pressure Processing (HPP)
a.k.a. Pascalisation

Hite (1899), Bridgman (1914)
Practical problems
Pressure vessels

Material industry, ceramics etc
First exploited by Japanese (1990s)
How does it work?
Food loaded into pressure vessel
Pressure applied to food by water
Pumping stopped
Held 5 ~ 15 minutes
Pressure released and food removed
No distortion - isostatic pressure
Equal in all directions
HPP equipment
Diagram of HPP system
How much pressure?
300 - 500 MPa

Roughly same as 10 tonne elephant standing on postage stamp (2 sq cm)
Examples of foods
Jams, fruit toppings, juices (Japan)
Guacamole (USA)
Fruit juices (France, USA)
Delicatessen style ham (Spain)
Effects on microorganisms
Inactivates most of them
Bacteria, moulds, yeasts, viruses, prions
Food poisoning organisms reduced by 4 log cycles
Addition of heat (<60 C) makes it more effective, especially for inactivating spores
Effects on food
Not much!
Retains freshness, colour, flavour, texture
No loss of Vit C
Degradative enzymes inactivated
Functional properties retained
Starch gelatinised in some
Possible to develop new texures
More information:
(includes review of other technologies)
Need well-engineered pressure vessel - expensive
May not kill spores
From: http://www.foodhaccp.com/memberonly/newsletter234.html
Inside Sadex Corp.'s Sioux City, Iowa food processing plant where ionizing radiation is used to kill bacteria, reduce spoilage parasites, inhibit sprouting and delay ripening.
Safety - food irradiation v. medical x-radiation
Energy (gamma) from Co - over 1 MeV
Energy from (medical) x-rays - up to 10 keV
eV = electron volt = 1.6 x 10 Joules (energy of 1 electron)
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