A Critical Review on the Effect of Gamma Irradiation on Microbiological Activity, Quality, and Safety of Food

Definition of Gamma Irradiation

A gamma ray, sometimes referred to as gamma radiation (sign γ), is a kind of electromagnetic radiation (Figure 1) penetrating and produced when atomic nuclei decay radioactively. It is made up of electromagnetic waves with the smallest wavelengths, which are usually shorter than X-rays with frequencies more than 30 exahertz (3×1019 Hz). In 1900, French scientist and physicist Paul Villard discovered gamma radiation while researching the radiation released by radium. Ernest Rutherford first identified two less invasive forms of decay radiation (discovered by Henri Becquerel) in 1900, naming them alpha (sign α) and beta (sign β) rays in increasing order of penetrating power. In 1903, he named this radiation “gamma rays” due to its comparatively high penetration of matter following alpha and beta rays [6].

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Safety of Food Irradiation

The Food and Drug Administration (FDA), the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and the United States Department of Agriculture (USDA) all see irradiated food as safe. A maximum overall average dose of 10 kGy was considered adequate for the majority of food applications [5].

Regulation of Food Irradiation

The FDA is in charge of controlling food radiation. Standards for radioactivity in food are regulated by the U.S. Food and Drug Administration (FDA). When deciding whether domestic food in interstate commerce or imported food poses a safety risk, the FDA establishes derived intervention levels (DILs), amounts of radioactivity in food. FDA evaluates each situation to see if preventative measures are required [5].

Labeling of Food Irradiation

In fact, the alterations brought about by irradiation are so slight that it is difficult to determine if a food has been exposed to radiation. Only after concluding that irradiating food is safe can the FDA approve a source of radiation for use on food. The FDA mandates that goods that have undergone radiation must display the global radiation sign. On the food label (Figure 2), look for the Radura symbol next to the words “Treated with radiation” or “Treated by irradiation”. Bulk items like fruits and vegetables must either have a label next to the selling container or be individually labeled. Keep in mind that proper food handling techniques used by producers, processors, and consumers are not replaced by irradiation. Foods that have been irradiated must be handled, stored, and prepared in the same way as foods that have not been irradiated since, if fundamental food safety precautions are not taken, they may still become contaminated with pathogens following irradiation [7].

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Unit of Irradiation Absorbed Dose

The dose in radiation processing refers to the quantity of energy that the target material absorbs. This is reported in units of kiloGray, where 1 kGy = 1,000 J/kg, or Gray, where 1 Gy is equal to 1 Joule per kilogram, as per the SI system. Dose Level. One joule of energy is equal to one gray (Gy) per kilogram of product (1 gray = 100 rads). 1000 Joules per kilogram is one kilogray. This is calculated by dividing the average energy applied to a unit of matter by its mass. The international unit of absorbed dosage is kGy.

The Allowable Amount of Gamma Radiation in Food Irradiation

International health and safety authorities have endorsed the safety of irradiation for all foods up to a dose level of 10 kGy.

Applications of Gamma Irradiation in Food Processing

Prior to protein extraction, defatted rice bran underwent gamma irradiation pre-treatment. Rice bran protein (RBP), rice bran protein hydrolysate (RBPH), and rice bran hydrolysate (RBH) were all included in the extracted content. For all extracts, but particularly RBH, where the yield and protein recovery improved by 21.2% and 13.8%, respectively, the extraction yields and protein recovery increased with irradiation. The irradiation-processed extracts were found to have a higher total phenolic content of RBP and RBH. The structure of rice bran may be altered by gamma radiation, resulting in a greater release of bioactive substances. In extracts treated by irradiation, antioxidant activity (ABTS, DPPH, FRAP, and MIC tests) dramatically increased [10].

Effect of Gamma Irradiation in Sterilization of Packaging Materials

Primary aromatic amines (PAAs), which include 2,4-diaminotoluene (2,4-TDA) and 4,4′-methylenedianiline (4,4’-MDA), are a class of organic compounds that the International Agency for Research on Cancer has classified as “possibly carcinogenic to humans”. Food contact materials (FCMs), which include laminated food packaging materials, colorful kitchen utensils, and colored napkins, have been found to contain residual monomers, isocyanate hydrolysis compounds or azo dyes contaminants. As 60Co-γ irradiation dose increased (5, 10 and 25 kGy), MDAs migration considerably decreased. For MDAs migration, high pressure processing (HPP) treatment (400 MPa/25 °C/15 min) reduced or preserved the same findings as the control. In terms of PAAs migration, 60Co-γ irradiation and HPP were generally considered to be safe sterilization techniques [11]. This result agreed with the previous publication about the effect of high pressure homogenization (HPH) for optimization of food processing, quality, and safety [12].

Effect of Gamma Irradiation on Microbial Decontamination of Food

Gamma irradiation as a non-thermal physical treatment has the potential to be effective at microbial decontamination. In this investigation, different gamma radiation dosages (2, 4, 6, 8 and 10 kGy) were applied to flour and grain of common buckwheat (Fagopyrum esculentum Moench). The control sample is the non-irradiated sample. All samples were tested for antioxidant activity (AOA), total phenolic content (TPC), total flavonoid content (TFC), rutin, and quercetin levels. In contrast to control samples, the values in the irradiation samples were greater. AOA, TPC, TFC, and rutin levels were increased in grain samples irradiated at 10 and in flour samples irradiated at 8, respectively. There was little change in the amount of quercetin. All test results were lower after 2 kGy of radiation. For buckwheat, gamma irradiation could be successfully applied as a novel preservation treatment [13].

Gamma radiation was applied to dried cassava chips at a dosage rate of 0.75 kGy/h with goal doses of 2.5, 5.0, 7.5, and 10.0 kGy. As a control, un irradiated chips were employed. Using established techniques, the dried cassava chips’ total viable count (TVC), total coliform count (TCC), yeast and mold count (YMC), Staphylococcus aureus count (SAC), Bacillus species count (BSC), and Salmonella count (SC) were all calculated. The dried cassava chips included coliform, Staphylococcus aureus, Bacillus spp., yeast, and molds, but not Salmonella. The bacteria found on the surfaces of the dried cassava chips were dramatically and dose-dependently decreased by gamma irradiation. The microbiological quality of dried cassava chips may be improved by radiation decontamination [14].

The impact of gamma irradiation on the microbiological stability of calyx powder from Hibiscus sabdariffa (Roselle) was identified. Samples of roselle calyx powder were placed in high-density polyethylene bags, irradiated at 0, 2, 4, 6, 8 and 10 kGy, and then left unattended for three months at room temperature (27 ± 3 °C). For microbiological analysis, samples were obtained at 0, 1, 2, and 3 months. The microbial load of the dried calyx powder was dramatically decreased by gamma irradiation dosages of (2, 4 and 6 kGy). In samples exposed to radiation at dose rates of 8 and 10 kGy, no microbial counts were found. This suggests that bacteria in the samples were entirely killed by gamma radiation doses of 8 and 10 kGy. Roselle calyx powder’s microbiological shelf life is increased by gamma irradiation-based decontamination [15].

The goal of another study was to determine how gamma irradiation (0, 2, 4, 6, 8 and 10 kGy) affected the physical- chemical, antinutritional, functional, microbiological and sensory characteristics of weaning food made with brown rice. With higher dosage, irradiated weaning food’s rehydration ratio (3.60-1.30%) and swelling power (2.59-1.08 g/g) both significantly decreased. With higher irradiation doses, the solubility index (1.32-6.18%) significantly rose. Increased radiation doses resulted in significantly lower moisture content (8.82-7.85%) and browning index (0.611-0.0.998). Irradiation dosages enhanced antioxidant activity, total phenol, β-carotene, iron, and calcium levels. With an increase in irradiation dose, the total plate count, sensory qualities, phytate, and oxalate contents all reduced [16].

All pathogens tested (B. cereus, L. monocytogenes, S. aureus, E. coli O157: H7, and S. Typhimurium) were more sensitive to radiosensitization when exposed to γ-irradiation in the frozen form of infant formula (IF) than in its powdered form, with a higher effect against B. cereus, S. Typhimurium, and L. monocytogenes [17].

Limitation on the Effect of Gamma Irradiation in Food Sector

It is noteworthy to mention that the gamma irradiation sterilization technique is merely based on biological effect on the living pathogens and it has no effect on the hazardous materials emerging as food processing contaminants such as 3-monocholoropropanediol (3-MCPD) emerging from the thermal processing of refined edible oils [18]. Gamma irradiation cannot destroy the chemical pesticides and toxins present in the food.