# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 4 Ionising Radiation (IOR)
The effect of ionising radiation on the rheology of foods is not confined to viscosity changes alone. The depolymerisation of biopolymers can result in changes in the textural and stability characteristics of foods, influencing properties such as the firmness, chewiness, and general mouthfeel. This becomes relevant in the use of hydrocolloids and gums in processed foods, where the breakdown of chains reduces their thickening ability and changes the final texture [133]. In addition, ionising radiation can enhance the oxidation of some food constituents responsible for the colour, flavour, and even the aroma of the food product. While these chemical modifications are useful in extending the shelf life and microbial safety of food, sometimes they concomitantly may induce off-flavours or off-colour development in food items like fruits, vegetables, and meat products [127; 132]. Therefore, radiation dosages have to be optimised with due care in order to strike a proper balance between food safety and the maintenance of high sensory and rheological qualities so that foods remain appealing for consumption while benefiting from the preservative effects of IOR. Most studies have been focusing on the inactivation of pathogens and spore-forming microbes by treating with ionising radiation to improve food safety and extend the shelf life. However, the physical treatment of food products by ionising radiation can cause radiation-induced changes in the rheological properties, texture, and quality. Changes in the chemical structure of food subjected to ionising radiation might occur because of energy interactions while it is being processed. The changes in the rheological behaviour of gamma-irradiated honey treated at doses of 0, 5, and 10 kGy were studied [134]. The results showed that the gamma radiation interaction with the honey at 5 and 10 kGy doses did not impact the viscosity significantly (\(p<0.05\)) or its Newtonian rheological behaviour. In a study on the influence of gamma irradiation on the texture, colour, and viscosity of potato starch at doses of 0, 5, 10, and 15 kGy, the results obtained demonstrated that while the texture became inversely proportional to the applied radiation dose, increasing doses promoted a slight rise in colour and decreased the viscosity [135]. Thus, unlike honey molecules, starch molecules undergo some degradation under irradiation, which resulted in a decreasing viscosity with increasing IOR doses. Hence, the application of IOR (a gamma or electron beam) in food processing has the capacity to induce molecular changes and degradation depending on the components of the food product such as starch. Consequently, the impact of IOR on rheology revealed that the viscosity decreased with the increasing radiation dose, according to a study that investigated the effects of ionising radiation on the rheological characteristics of degreased seasoned flours (carbohydrate (78.9%), lipids (13.6%), protein (2.1%), and dietary fibres (7.8%)) at doses of 0 (control) and 5 kGy [136]. This can be ascribed to radiation-induced molecular structure degradation. In addition, starch's gelling properties, as well as the viscosity and structural rheological stability of its gels, seem to be the key elements influencing the potential usage of starch in a variety of food products. In another study on similar food products, the effects of ionising radiation on the rheological and physicochemical properties of bacon and traditional farofa were investigated at doses of 1, 5, and 10 kGy [137]. The findings revealed that at 5 and 10 kGy, irradiation significantly affected the farofa's viscosity profile and textural properties, including its cohesiveness, hardness, and springiness.