# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 4 Ionising Radiation (IOR)
However, as the total absorbed dose increased beyond this threshold, the viscosity steadily declined due to the degradation of the polymer structure, ultimately affecting the gel-forming and thickening properties of the gum sample. The irradiation process has been shown to be safe. The World Health Organisation (WHO), the Scientific Committee on Food, which provided scientific advice to the European Commission (EC) on food safety, the Food and Agriculture Organisation (FAO) of the United Nations, and the International Atomic Energy Agency (IAEA) have all agreed that food irradiation up to doses of 10 kGy is accepted internationally for foods destined for human and animal consumption and does not make food radioactive, nor pose any health risks to consumers [125]. The FAO, IAEA, and WHO conducted a group study in 1997  
Figure 3: Pictorial representation of the ionising radiation process in a typical food system [120]. that examined the effects of exposing food to radiation above the recommended dose of 10 kGy [126]. The study found that few food samples could withstand such high doses without losing their sensory qualities, but that irradiating animal feed with radiation doses higher than 70 kGy showed no health issues in the test subjects. Therefore, it was determined that it is safe to expose food to ionising radiation of any dose as long as it is carried out to accomplish a technological goal, does not cause nutritional deficiencies, and does not affect the food's safety, such as the decontamination of spices, dried herbs, and vegetable seasonings, which may require doses up to 30 kGy to ensure microbial safety [125; 127]. Factors that affect the effectiveness of ionising radiations include the presence or absence of oxygen, the composition of the medium, the food density, and thickness [5; 6; 91; 127; 128]. IOR technology influences food rheology by inducing structural changes in biopolymers, such as depolymerisation, which can decrease the viscosity of hydrocolloid solutions. Certain foods, such as protein products and milk, are more susceptible to radiation-induced changes due to their complex biochemical composition and sensitivity to oxidative and structural alterations [129]. The irradiation effect on proteins is a function of various factors, including the protein structure (globular or fibrous), state (native or denatured), composition, the presence of other molecules, and environmental conditions such as the dose, dose rate, temperature, and oxygen levels [130; 131]. Irradiation causes structural changes that cause proteins to aggregate or unfold through the breakage of the peptide chains, disulfide bonds, and secondary interactions including hydrogen and hydrophobic bonds. Also, irradiation enables the creation of ionic and free radical intermediates, which enhance oxidative reactions. These reactions can result in protein oxidation, creating carbonyl groups, a loss of sulfhydryl groups, and cross-linking, ultimately altering protein functionality. Over time, oxidative modifications cause texture alterations, a reduced water-binding capacity, denaturation, the modification of functional properties, and reduced emulsification properties [131]. Thus, while irradiation is an important preservation technique, its oxidative effects must be properly regulated to maintain food stability, sensory characteristics, and the overall quality. Research shows that the viscosity of honey remains stable at doses up to 10 kGy, while higher doses beyond this threshold may affect sensory and rheological properties, such as the consistency and texture [121]. Similarly, in dairy products, doses above 5 kGy can induce protein denaturation which results in undesirable textural changes [129], while in hydrocolloids, structural breakdown can occur at doses exceeding 8.17 \(\pm\) 0.2 kGy, leading to a reduced viscosity and gel strength [124]. These findings underscore the importance of optimising the IOR application to balance microbial safety with the retention of the food quality [127; 132].