# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 4 Ionising Radiation (IOR)  
Gamma electron beam/X ray is used in the ionising radiation process to reduce microbial action and decrease enzymatic activities in agro-food products [6; 115]. Ionising radiation is a pasteurisation process, and no heat is added in this method. Microorganisms are inactivated due to the breakdown of their cellular structure and fragmentation process. However, the efficacy and impact of ionising radiation are dependent on the food composition, radiation dose, and oxygen availability [116]. Lipid-containing foods can become rancid by lipid oxidation, whereas pigment degradation due to excessive doses of radiation can lead to discolouration in fruit, vegetables, and meat products [117]. The study by [PERSON] et al. [118] on the effects of gamma irradiation on Ponkan fruit revealed severe damage induced by excessive doses (>1 kGy), including accelerated aging and browning. Small doses (0.25-1.0 kGy) were attempted to assess their action on _Penicillium digitatum_ inhibition and on the fruit quality. The study showed a reverse association between the gamma dose and the growth of fungi, and concluded that gamma radiation induces damage in the fungal membranes and leakage of intracellular material. However, while 1.0 kGy effectively inhibited fungal growth, it also led to the accelerated aging of fruit, a loss in weight, and browning. Hence, 0.5 kGy was found to be optimal for inhibiting the rot of fruit while conserving the maximum amount of nutrients and weight. Of all the dosages, the fruit samples subjected to 0.5 kGy contained maximum levels of total soluble solids (10.5%) and vitamin C (17.5 mg/100 g), as well as a minimal loss of titratable acidity (0.68%), even after storage. Browning was observed in all the irradiated samples, which increased with the dose and storage time. Therefore, while ionising radiation can enhance the shelf life, it can potentially cause undesirable sensory changes, depending on the dose [118]. Hence, the ionising radiation process is not valid for all types of food, such as milk and protein, as their respective food colour, odour, and flavour can be altered. Some foods soften and lose their original colour at high-level doses [91]. The irradiation of food has been extensively studied due to its efficiency as a tool for preserving food. Several studies investigated the potential changes in the structures of food due to irradiation, with most of them focusing on alterations in terms of the texture of solid foods. Studies examining fluids have mainly explored the depolymerisation of biopolymers [32]. When photons interact with food molecules, charged ions are formed, and super-reactive free radicals react among themselves [6]. There are several steps towards utilising and applying ionising radiation in food preservation. The first process is the generation of gamma rays via cobalt-60 or Cesium-137. This is followed by the application of X-ray beams that are passed at 5 MeV. Finally, a generated high-electron beam is emitted via accelerators, and an energy level of 10 MeV or less is maintained [6; 119]. This is illustrated in Figure 3.  
The effect of ionising radiation on food rheology is mostly dependent upon the dose. It has been reported that the viscosity of honey is not impaired up to doses of 5 and 10 kGy, as shown in the study by [PERSON] et al. [121] where ionising radiation at the dose of about 10 kGy effectively decreased the number of microorganisms and its antibiotic activity and stability (5-HMF), without influencing the organoleptic value of honey. In contrast, the viscosity and consistency of hydrocolloid solutions decrease with increased radiation [64; 122; 123]. In the study by [PERSON] and [PERSON] [124], the gum solution's apparent viscosity initially increased as the radiation dose rose from 0 to approximately 8.17 \(\pm\) 0.2 kGy, indicating an improvement in the emulsion stability.