# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 5 Ultraviolet and Pulsed Light
For instance, UVC treatment at the wavelength of 253.7 nm is considered germicidal against microorganisms and has been successfully applied to improve microbial safety and maintain the sensory quality of fresh juice and dairy products with little oxidation [153; 154]. As shown in Figure 4, when microorganisms are exposed to UVC light, the light penetrates through their cell wall and disrupts the structure of their DNA molecules, prohibiting reproduction. According to [PERSON] et al. [155], apple juice treated with a monochromatic low-pressure (LPM) lamp set at 253.7 nm and 10 mJ/cm\({}^{2}\) only had a 1.30% decrease in the vitamin C concentration, demonstrating the potential of UV-C in the treatment of fruit juices without reducing their sensory quality. However, prolonged UV exposure can degrade light-sensitive vitamins, such as vitamin C and certain B-complex vitamins, leading to a decline in their nutritional value. Studies have shown that riboflavin (vitamin B2) is particularly susceptible to UV degradation, which could impact the overall micronutrient composition of treated foods [156]. Furthermore, natural pigments such as carotenoids and anthocyanins are prone to degradation under intense and prolonged light exposure [157]. Similarly, PL treatment at 0.5-9.6 J/cm\({}^{2}\) has been reported to inactivate pathogens effectively in fresh-cut fruits and vegetables without affecting their textural quality. The study by [PERSON] et al. [158] investigated the effect of different PL fluences (1.5, 4.2, 6.9, 9.6, and 12.3 J/cm\({}^{2}\)) on the physical and microbiological quality of pennywort (_Centella asatica_) stored at 4 \({}^{\circ}\)C. The results showed that fluences of 6.9, 9.6,and 12.3 J/cm\({}^{2}\) reduced the microbial counts significantly, with the highest inactivation at 9.6 and 12.3 J/cm\({}^{2}\). However, PL at 6.9 J/cm\({}^{2}\) was determined to be optimum, as it was effective in reducing _E. coli_ contamination without affecting the texture and extending the shelf life by approximately four days. SEM showed that PL disrupted the bacterial cell membrane, which was responsible for its antimicrobial efficacy. Interestingly, the two higher fluences (9.6 and 12.3 J/cm\({}^{2}\)) altered the colour of the leaves, suggesting the necessity of dose optimisation in PL applications. Additionally, in lipid-rich foods, intensive bursts of PL energy and prolonged UV exposure can lead to lipid oxidation, particularly in unsaturated fatty acids. This can cause the formation of off-flavours and reduce the sensory quality due to the accumulation of lipid peroxidation products and their interference with taste and aroma [12]. Importantly, UV and PL technologies further affect other important rheological properties, including the elasticity, firmness, and flow behaviour. For instance, UV-induced cross-linking in proteins and polysaccharides might build more intensive gel matrices that can enhance the firmness and stability of some food products, such as jellies and dairy-based ones, which provides a longer shelf life for foods [159]. On the other hand, PL technology has been reported to cause microstructural modifications in food tissues due to its high energy pulses, inducing cell wall loosening in fruits and vegetables [141]. These features can lead to improved juice extraction efficiencies and an enhanced water retention capacity, making PL particularly valuable to produce beverages and fruit-based products [6; 160]. However, these treatments should not be overused because it could result in undesired effects such as over-softening or a loss of natural texture that may reduce the quality of the products. In addition, UV and PL can initiate oxidative reactions in some food components, which may alter their sensory properties, such as the flavour and colour. For example, UV light, if applied for a longer period, may cause browning in light-sensitive foods like milk or fresh juices due to the decomposition of ascorbic acid and polyphenols [153].