Food Irradiation Basics

Food Irradiation

• Food irradiation is a process where food is exposed to a controlled amount of ionizing radiation to achieve desired objectives.
• It's considered a food additive.
• It can sterilize packaging materials, destroy pathogens (e.g., Salmonella), prevent spoilage by microorganisms, delay ripening, inactivate parasites, and inhibit sprouting in vegetables.
• Cold pasteurization is another name for ionizing radiation. It has the same goal as thermal pasteurization for liquid foods (e.g., milk), but without significantly raising the product's temperature.
• It's used in over 40 countries on more than 100 food items, including potatoes, onions, cereals, flour, fresh fruit, and poultry.

Electromagnetic Spectrum

• The electromagnetic spectrum displays various types of electromagnetic radiation.
• It ranges from cosmic rays to radio waves, with visible light being a part of it.
• Radiation types include (from high to low frequency/long to short wavelengths): Gamma rays, X-rays, Ultraviolet (UV), Visible light, Infrared (IR), Microwaves, and Radio waves.
• Sunlight contains various types of infrared radiation.

How Irradiation Works

• The energy from irradiation breaks bonds in DNA molecules of microbes resulting in defects in their genetic instructions.
• If this damage can't be repaired, the microbe dies or can't reproduce.
• The effectiveness of the process depends on the organism's sensitivity to radiation, its DNA repair rate, and the amount of DNA in the organism.
• Parasites and insect pests, with much DNA, are quickly killed. Bacteria, with less DNA, require a higher dose.
• Viruses are generally resistant to irradiation doses used for food.
• Radiation works through two mechanisms: direct interaction with cell components (primarily targeting chromosomal DNA and affecting cell membrane structure) and indirect action from radiolytic products like water radicals.

Types of Radiation Used in Food

• Gamma rays: Generated by the spontaneous disintegration of radioisotopes (e.g., cobalt-60 and cesium-137).
• Accelerated electrons: Generated by electron guns and accelerators, increasing electron speed to the speed of light.
• X-rays: Generated by colliding electrons with metallic targets (e.g., tungsten, gold).

Gamma Rays (Specifics)

• Gamma rays are high-frequency electromagnetic energy released by radioactive substances.
• Common radioactive substances in food irradiation include cobalt-60 (half-life of 5.3 years) and cesium-137 (half-life of 30 years).
• Irradiation using gamma rays requires shielding concrete.

How Irradiation Works (Detailed)

• The process involves putting food in special, radiation-resistant containers and exposing them to a controlled radiation source for a specified period.
• The radioactive source (such as cobalt-60) emits gamma rays which can penetrate food up to several feet.
• This process typically does not make the surrounding area radioactive.
• The process may be used for treatment of cancer, sterilization of medical equipment, and sterilization of other industrial equipment.

Advantages of Irradiation

• Reduces disease-causing microorganisms.
• Doesn't change nutritional value significantly.
• Doesn't make the food radioactive.
• A safe and effective technology for preventing foodborne illness.
• Increased shelf life for fruits and vegetables, inhibiting sprouting and slowing ripening.

Advantages of Various Irradiation Methods

• Gamma rays: Up to 95% of emitted energy is usable. Penetrates deeply (e.g., food >12 inches thick; similar to X-rays). Provides uniform dose distribution throughout the food. Decays into non-radioactive elements (nickel and barium). Low environmental risk.
• Accelerated electrons: Can be turned on/off as needed. No radioactive material required. Depth of penetration is relatively shallow (limited to approximately 3 cm, or 1 inch.) Two opposing beams can double penetration.

Disadvantages of Various Irradiation Methods

• Gamma rays: Co-60 pencils require frequent replenishment and are "always on."
• Accelerated electrons: High electricity consumption; more complex and costly apparatus with higher maintenance.

X-rays

• Produced by colliding electrons with metal targets (e.g., tungsten, gold.)
• Better penetrability than electron beams.
• Much lower than the efficiency of electrons converted to X-rays (efficiency <10%).
• Recent (new technology).
• X-ray machines have similar functionality like imaging equipment used in hospitals and clinics, requiring shielding.

Radiation Dose

• Dose is measured in Grays (Gy) – amount of energy absorbed per kilogram of food.
• Dose used depends on the specific food, desired outcome and type of organism present in it. International standards specify maximum safe dosages.
• Higher doses are needed to control bacteria than parasites.
• Doses are characterized differently for different types of food, and differ depending on the objectives of irradiation.

Effect of Irradiation on Food Quality

• Radiation can cause free radical formation; this can lead to off-flavors (e.g., meat and eggs), changes to amino acids/ proteins, and reduced gelling power (softening) in some foods.
• Vitamin loss is possible.

Applications in Food Industry

• Inhibiting sprouting (e.g., potatoes, onions).
• Delaying ripening and aging in plants.
• Increasing juice yield (improving hydration).
• Insect sterilization (prevents proliferation).
• Eliminate risk of contamination by virulent E. Coli, salmonella and other bacteria.
• Absolute sterilization of foods for immune deficient patients and space programs.
• Treating meat, poultry, spices, and bakery products.

Types of Radiant Energy

• Ionizing radiation (e.g., gamma rays, X-rays): High enough energy to dislodge electrons from atoms or molecules changing them to ions.
• Ultraviolet light, Infrared: Lower energy to excite electrons and cause changes to certain food components, but not necessarily change all of them into ions.

Additional Notes

• The presence of a radura logo on a food product indicates the use of irradiation.
• Irradiation is a way to increase shelf life and reduce spoilage.