Preservation of Food by Radiation • UV radiation • Ionizing radiation - irradiation
What is radiation? • This word has a negative connotation - for most consumers it means the emission of harmful radioactivity. • Radiation means exposure to radiant energy. • Radiant energy is energy that moves at speed of light but varies in intensity with both electric and magnetic fields. • Ionizing radiation are rays with enough energy to strip and electron from atom (gamma rays, X-rays)
Human and Radiation • We are exposed to 31 mrem per year from cosmic radiation. • We are exposed to 24 mrem per year of gamma radiation from food, air, water • We are exposed to 40 mrem per year of gamma radiation from rocks and soils • A dose of 100-200 rads produces nausea, vomiting and diarrhea. • Survival from doses >500 rads all over the body is unlikely due to depression bone marrow resulting in very low white counts.
Principle of food preservation by radiation To kill microorganisms, parasites andinsects
The entire spectrum of radiation can be divided into: • Low frequency, long wavelength, low quantum energy of radiation 10-6 to 104 m. The effect of this radiation on microorganisms is related to their thermal effects on food. • High frequency, shorter wavelength, high quantum energy radiation - may excite or breakdown organic compounds and microorganisms
The shorter radiation energy applied to food can be divided into: • Lower frequency, lower energy radiation - UV radiation - sufficient energy to excite. • Higher frequency, higher energy radiation energy - ionizing energy - capable of breaking individual molecules.
Bactericidal effect of UV and ionizing radiation depends on: • The kind of microorganisms • The number of microorganisms • The composition of food • The presence or absence of oxygen • The physical state of food • The condition of microorganism
UV radiation • The most effective is radiation near 260 nm. This wavelength is strongly absorbed by purines and pyrimidines. • The source of UV radiation -quartz-mercury lamp or low pressure mercury lamp. These lamps emit radiation at 254 nm.
Effectiveness of UV radiation is affected by: • Time • Intensity: power of the lamp, the distance of the lamp from the object, the kind and amount of interfering materials. • Penetration : nature of the materials; the rays only affect the outer surface of radiated foods
Resistance of microorganisms to UV • Bacterial spores are 2-5 times more resistant than wegetative forms. • The yeasts are 2-5 times more resistant than bacteria. • The molds are 10-50 times more resistant than bacteria.
Uv radiation doses (mWsec*100) needed for 1 log cycle reduction of certain microorganisms
Food industry uses UV for: • Treatment of water for beverages • Aging meats • Treatment of knives for slicing breads • Packaging of sliced bacon • prevention of growth of film yeast on pickles • killing spores on sugar crystals • storage and packaging of cheese • treatment of air used for storage or processing of foods
Food Irradiation • Permitted in 30 countries • 18 countries are actually irradiating food • Canada allows irradiation of potatoes, onions, spices, wheat and other grains, but irradiated food is not being sold here. • Irradiation of food is not permitted in Germany, Britain, and Scandinavian countries.
Consumers’ reactions to food irradiation • The rejectors, 5-10 % of consumers • The confused consumers - 55-65% of consumers • The acceptors, 25-30% of consumers
The Rejectors: • Irradiation of food is rejected because of opposition to the use nuclear energy, environ -mental concerns etc. • monumental effort needed to change this group
The Confused Consumers: • They like a food free of pathogen and insects and may see irradiation as a means to achieve this, but are afraid something new and not well understood. • Needs a lot of credible information to address each of the concerns and carefully outline the benefits.
The Acceptors • This group has a positive attitude but still could by groups voicing concerns • This groups needs messages that give risks and benefits. Data must be given that will refute or support the concerns
Food irradiation • Who benefits • Is irradiation safe? • Does irradiation prevents foodborne illness? • Are radiation-resistant bacteria formed? • Are there any alternatives to irradiation?
Who benefits • Consumer - elimination disease-causing organisms, extension of shelf life • Food marketers - reduce food spoilage • Nuclear industry - new justifi -cations and potential income
Is Food Irradiation Safe? • Too much conflicting evidence as number of studie showing that food irradiation is safe is almost similar to number of studies showing adverse effect. • The 1980 report of the FAO/IAEA /WHO Joint Expert Committee concluded that a dose of 10 kGy presents no toxicological hazard and introduces no special nutritional or microbial problems.
Ionizing radiation includes: • X-rays • alpha rays • beta rays • gamma rays • protons • neutrons
Irradiation of foods can be classified as: • Radappertization -” radiation sterilization” - it implies high dose treatments, with the resulting product being shelf stable. • Radurization - “radiation pasteurization” - low dose treat- ment with the intent to extend a product’s shelf life
Irradiation of foods can be classified as: • Radicidation - a low dose radiation pasteurization with the intent to eliminate a particular pathogen • Picowaved food -term used to label food treated with a low level of ionizing radiation
Other terms used: • Disinfestation - refers to radiation treatments whose objective is to kill or inactivate insects or parasites. • Delayed of Ripening and Senescence - refers to radiation treatment of fruits and vegetables whose usual spoilage is overripening. • Sprout Inhibition - refers tp radiation treatments used to prevent or delay sprouting.
Units • Rad is a unit of radiation dosage being an equivalent to the absorption of 100 erg per of irradiated food • Gray = 100 rads • Electronovolt is an energy gaines by an electron in moving through a potential difference of 1 volt.
Source of ionizing radiation • Cobalt 60 • Cesium 137
Dose determining factors • Resistance of food - organoleptic quality • Resistance of microorganisms • Resistance of enzymes • Cost
Thresholds dose for detectable off-flavors (krad) from meats irradiated at 5 C to 10 C • Turkey 150 • Pork 175 • Beef 250 • Chicken 250 • Lobster 250 • Trout 450 • Halibut 500 • Lamb 625 • Horse 650 • Bear 850
The most radiation resistant bacteria of concern is Clostridium botulinum D=0.4Mrad • Resistance of enzymes - 5Mrad
Radiation effects: • Direct effects • Indirect effects are due to formation of H2O2 and free radicals: *OH, *HO2. These species are products of water radiation.
Indirect effects can be limited by: • Irradiation of frozen food • Irradiation in vacuum • Addition of radical scavengers like ascorbic acid.
Changes in food include: • In meat-increase in pH, increase in carbonyl compounds, H2S • In fats - destruction of natural antioxidants, oxidation of fats • Loss of vitamins such as thiamine, C and B6