Gamma irradiation and its effect on the quality of Meat

Gamma irradiation for food

The process of gamma irradiating food involves subjecting it to ionizing radiation. The shelf life of food products is increased, microbes are eliminated or inhibited from growing, and insect infestation is managed. Gamma rays are a powerful type of electromagnetic radiation that may pass through objects and kill insects and bacteria.

Here are some key points about gamma irradiation for food:

How it works:

Food products are exposed to gamma rays emitted by a radioactive source, typically cobalt-60 or cesium-137. These rays pass through the food, interacting with the cells of microorganisms, insects, and other pests. The high-energy radiation damages the DNA or RNA of these organisms, preventing their ability to reproduce and causing their death.

Safety:

Gamma irradiation has been extensively studied and approved by various international organizations, including the World Health Organization (WHO), the Food and Agriculture Organization (FAO), and the International Atomic Energy Agency (IAEA). It is considered safe when applied within recommended dosage levels and proper control measures. The process does not make the food radioactive and does not significantly affect its nutritional value.

Microbial control:

Gamma irradiation is effective in reducing or eliminating a wide range of microorganisms, including bacteria, molds, yeasts, and parasites. It can significantly reduce the risk of foodborne illnesses caused by pathogens such as Salmonella, E. coli, and Listeria. The exact dosage required depends on the specific food product and the target microorganism.

Insect control:

Gamma irradiation is also used to control insect infestation in stored grains, dried fruits, and other food commodities. It disrupts the insects' reproductive cycle, sterilizing them and preventing population growth. This helps in preventing post-harvest losses and reducing the need for chemical insecticides.

Shelf-life extension:

By controlling microbial growth and insect infestation, gamma irradiation can extend the shelf life of food products. It inhibits the spoilage caused by microorganisms, molds, and insects, helping to maintain the quality and freshness of the food for longer periods.

Approved applications:

Gamma irradiation is approved for use in several countries for various food products, including fruits, vegetables, spices, grains, meat, poultry, seafood, and certain food ingredients. The specific regulations and dosage requirements vary depending on the country and food item.

Gamma irradiation is a useful tool for food preservation, but there are a variety of other options as well. Depending on the particular food product and the intended result, other techniques can also be utilized, such as heat treatment, freezing, canning, and high-pressure processing.

Effect on the quality of Meat

Gamma Radiations is the best method to control pathogens in meat. It greatly affects the quality changes such as color, odor, and flavor in raw and cooked meat. These factors affect the consumer’s acceptance criteria.

Color:

Color is important quality parameter which influence customer acceptance. The color variations depend upon irradiation dose, animal species, muscle type, and packaging type. Usually, light meat produces pink color whereas dark meat become brown or gray after irradiation treatments. After applying irradiation redness increases in the observed lion of the beef meat. It depends on the dose and Lab values that was measured trough colorimeter. A bright pink color appeared on surfaces if meat thus increase in a value. Moreover, hue and saturation were also increased upon gamma treatment. These radiations give meat the same color as sodium nitrate in curing of meat. This color variation is observed in both cooked and raw meat.

When irradiations are applied on the meat activated oxygen atom react with iron-porphyrin (heme group) and imparts a bright pink color to the meat. The L value was increased but b value hasn’t any influence on meat color. Thus, both gamma treatment and sodium nitrite give the same color. Moreover, globin portion is denatured and addition of another nitric oxide molecule in the iron-porphyrin ring. When gamma radiations apply on vacuum packaged meat it develops purple color which indicates absence of oxygen and bright red color in presence of oxygen. Thus, to conclude the effect on meat color shows that irradiations increased the color of meat significantly but color decreases as well on storage of meat.  These color changes occur mainly due to alterations in the iron ion of myoglobin.

Texture:

Radiations treatments affects the structure of intracellular skin and muscles. Further it activates some enzymes that accelerates the rate of glycolysis. Thus, gamma rays effect the post mortem inspection and morphological properties of meat. Shorting of sarcomere does not occurs however irradiated muscles swells on gamma treatment. This shows that irradiations disrupt the actin and myosin bonds. Thus, sarcomere length shortening does not occur due to denaturation on the fibrous proteins. i.e., A research shows that this happens more at 4 °C during storage. Rapid decline in pH was observed in the irradiated muscle of meat. After gamma radiations the ageing period shortens and anaerobic metabolism of meat accelerates. Thus, irradiated meat sample preserved a good quality and texture during 21 days of chilled storage, however the control sample showed putrefaction means slimy textured meat because Histamine content was reduced after irradiation treatment, such decrease strongly it correlates with the applied dose level of gamma rays.

Flavor:

Flavor is produced by combining the basic tastes (sweet, sour, bitter, salt, and umami) obtained from water-soluble molecules and odor produced from volatile compounds present in the product from the beginning or produced via numerous actions.  The precursor compounds of fresh meat are responsible for the production of favorable and unfavorable odors. Acids, alcohols, aldehydes, aromatic compounds, esters, ethers, furans, hydrocarbons, ketones, lactones, pyrazines, pyridines, pyrroles, sulphides, thiazoles, thiophenes, pyrroles, and oxazoles are some of the flavor and different odor volatile compounds found in meat. 

The flavor of the normal meat is different from irradiated meat because of the impact of the radio lytic byproducts. The main challenge with the irradiated meat and poultry has been the formation of an unpleasant flavor. The purpose of irradiation research in the 1950s and 1960s was to sterilize the product, which required the use of high-level doses. The high dosages, along with a variety of processing factors, resulted in a flavor known as "irradiation flavor." Irradiation flavor has been defined as a "scorched flavor," but it has been described as a "goaty" or "wet dog" flavor. The production of irradiation flavor is dose dependent, according to evidence, and the threshold dose for noticeable flavor differs per species. 1.50 kGy, 1.75 kGy, 2.5 kGy, and 2.5 kGy, respectively, are required for a detectable flavor in turkey, hog, beef, and chicken.

The irradiation odor of meat is caused by volatile Sulphur compounds produced by irradiation. It also speeds up the oxidation of lipids in meat. Unsaturated fatty acids are the most important component of the lipid fraction. Irradiation may result in the generation of free radicals at the carbonyl groups and carbon double bonds because they are electron-deficient. Hydroxyl radicals (OH) are thought to be the initiators of lipid oxidation in muscle tissue because they react with conjugated systems. After that, traditional mechanisms for autoxidation is start. These changes will cause off flavors in meat. There is less change in flavor of poultry because of low concentration of unsaturated fatty acids.

Tenderness

Tenderness is a desirable characteristic since tender meat is softer, easier to chew, and more appealing than tough meat. The meat tenderness was considerably enhanced by irradiation (1 to 6kGy). Similarly, irradiation breaks down myofibrils proteins, which are regulated by the presence of calcium-dependent proteases or calpains, which are known to affect meat tenderness. Similarly, it is claimed that the meat tenderness is caused by physical rupture of myofibrils. The radiation also enhances the collagen and protein solubility which increase the tenderness of meat. The radiations also breakdown the myofibril and sarcoplasmic protein of the meat. Radiations break the S-S bridges and split the hydrogen in the meat which help to increase the tenderness of meat.