BY: M.SC. MOHAMMED SABAH Chapter 8. Irradiation

Ionising radiation takes the form of -rays from isotopes or, commercially to a lesser extent, from X-rays and electrons. It is permitted in 38 countries to preserve foods by destruction of micro-organisms or inhibition of biochemical changes.

The main advantages of irradiation are as follows:  there is little or no heating of the food and therefore negligible change to sensory characteristics  packaged and frozen foods may be treated  fresh foods may be preserved in a single operation, and without the use of chemical preservatives  energy requirements are very low  changes in nutritional value of foods are comparable with other methods of food preservation  processing is automatically controlled and has low operating costs. 1- Advantages and disadvantages

major disadvantages  the process could be used to eliminate high bacterial loads to make otherwise unacceptable foods saleable  there will be a health hazard if toxin-producing bacteria are destroyed after they have contaminated the food with toxins  the possible development of resistance to radiation in micro- organisms  loss of nutritional value.  until recently, inadequate analytical procedures for detecting whether foods have been irradiated

What Can Irradiation Do? Prevent Food Poisoning By Reducing – E. Coli )157:H7 (Beef) – Salmonella (Poultry) – Campylobacter (Poultry) – Parasites Prevent Spoilage by Destroying Molds, Bacteria and Yeast Control Insects and Parasite Infestation Increase Shelf Life by Slowing Ripening of Fresh Fruits and Vegetables

2. Theory x-rays and electrons are distinguished from other forms of radiation by their ionising ability (that is they are able to break chemical bonds when absorbed by materials). The products of ionisation may be electrically charged (ions) or neutral (free radicals). These then further react to cause changes in an irradiated material known as radiolysis. It is these reactions that cause the destruction of micro-organisms, insects and parasites during food irradiation.

3- Types of Radiation Energy Are Used for Treating Foods Two types of radiation sources are commonly used for food treatment. 1- The first is a tightly sealed metal container of radioactive elements cobalt 60 or cesium 137 that produce gamma rays. The rays are directed onto the food being irradiated, but the food itself never comes into contact with the cobalt or cesium source. 2- The second type of radiation source is a machine that produces either X-rays or high-energy electrons. Because of the physical characteristics of these sources, no radioactivity can be induced in food thus treated, no matter how much energy (dose) is absorbed by the food or how long the food is irradiated. ( L. Paisan. 2003).

Source = L. Paisan. (2003)

4. Effect on micro-organisms The reactive ions produced by irradiating foods injure or destroy micro-organisms immediately, by changing the structure of cell membranes and affecting metabolic enzyme activity. However, a more important effect is on deoxyribonucleic acid (DNA) and ribonucleic acid molecules in cell nuclei, which are required for growth and replication

Microbial destruction by irradiation: A, Pseudomonas sp.; B, Salmonella sp.; C, Bacillus cereus; D, Deinococcus radiodurans; E, typical virus.

 A common consumer concern is whether irradiation adversely affects the nutritional value of food. The fact is that irradiation treatments do not change the nutritional quality of foods any more than do other methods of food processing such as cooking, freezing or canning.  Any changes in nutritional value caused by irradiation depend on a number of factors: 1- radiation dose 2- the type of food 3- temperature and atmosphere in which irradiation is performed (e.g., presence or absence of oxygen), 4- packaging and storage time Nutritional and sensory value

 Main components of foods such as proteins, fats and carbohydrates are changed very little by irradiation, even at doses higher than 10 kGy. Similarly, the essential amino acids, minerals, trace elements and most vitamins are not significantly altered by irradiation.  Some vitamins riboflavin, niacin and vitamin D are fairly resistant to irradiation, but vitamins A, B1 (thiamine), E and K are relatively sensitive.  Their sensitivities depend on 1- the complexity of the food system, whether the vitamins are soluble in water or fat. 2- the atmosphere in which irradiation occurs. For example, a solution of thiamine in water lost 50% of the vitamin after irradiation at 0.5 kGy. In contrast, irradiation of dried whole egg at the same dose caused less than 5% destruction of the same vitamin

 Results of studies on the effects of irradiation on vitamin C in fruits and vegetables often are conflicting. Some studies reported an effect only on ascorbic acid, while others reported an effect on total ascorbic acid, which is a mixture of ascorbic and dehydroascorbic acid, both of which provide vitamin C activity.

6. Effects on Sensory Quality of Foods  Similar to other processes, irradiation causes certain chemical changes in food that may, under some circumstances, noticeably affect food quality  Some foods react unfavorably even to low doses of irradiation. Milk and dairy products are among the most radiation-sensitive foods.  A dose as low as 0.1 kGy will impart an off-flavor to milk that most consumers find unacceptable; thus milk and dairy products are generally not irradiated. Irradiation of some fresh fruits and vegetables may cause softening because of the breakdown of cell walls.  High-dose irradiation sterilization could induce “off” flavors in many types of meat products if the process is not done properly.