## 4 Stimulation Process of UV-C
### Low UV-C Dose Stimulation  
A number of studies investigated different properties of postharvest products when exposed to UV-C irradiation by considering a range of UV-C doses. In the subsequent sections of the review, we discuss the stimulation process of UV-C by classifying low, moderate, and high doses. The classification is mostly based on the relative comparison among the treatment levels and control samples taken in the particular work of art. There is no clear demarcation set for the UV-C dose irradiation from low to high. This is due to the fact that the change induced by UV-C is varied in different products. The effect might even be different among different varieties of the same product. However, the classification takes account of the proposition and findings of previous research. A work by a researcher depicted that a fruit could resist the effect of UV-C dose up to 4.1 kJ\(\cdot\)m\({}^{-2}\)[106]. Furthermore, the latest research carried out an experiment on the effect of low UV-C dose in the range below 4 kJ\(\cdot\)m\({}^{-2}\)[107].  
Recent work on the sprouting suppression and quality attributes of potato tuber exposed to low UV-C dose indicated that the role of UV-C light is not only limited to the anti-germicidal effect, but also enables resistance to damage repair and sprouting [108]. A low UV-C dose is reported to induce a hormetic effect on vegetative crops without damaging the crop, which is termed as UV-C hormesis, making use of a harmful low dose of irradiation to induce a favorable stress response on crops [109]. In addition to the hormetic effect, the plant crop is able to offer health-promoting advantages when used by the customer which is referred to as xenohormesis [110]. This is due to the phenolic compound phytoalgebras having antioxidant properties further inducing a secondary resistance in the end user's body [111]. Basically, the purpose of using non-thermal technology on harvested crops is primarily to maintain the quality without undergoing damage, which in turn delays senescence. The influence of UV-C offers a pronounced effect over UV-A and UV-B in the process of delaying senescence, and over the other non-thermal processes UV-C is considered as releasing optimized oxidative stress for defense against germ and wound response [112; 113; 114; 115]. These effects were well demonstrated by the experiment conducted on lettuce, tomatoes, peaches, and strawberries [116; 117; 118; 119]. From a molecular perspective, the plant develops the response by producing ROS (reactive oxygen species) that signals the physiological modification in the chloroplast, mitochondria, DNA and produces secondary metabolites [120; 121]. An experimental study performed on tomato fruit in response to UV-C treatment elucidated that the response of the plant involves much greater expression of a number genes responsible for cell wall disassembly, which may be linked to physiological changes, damage resistance, and most importantly delaying softening or maintaining the firmness of the final product [122]. A recent investigation of broccoli florets exposed to a hormetic dose of 1.2 kJ\(\cdot\)m\({}^{-2}\) of UV-C radiation was able to maintain the lowest weight loss as compared to untreated samples [123]. Higher firmness and delayed softening at a lower UV-C dose on strawberry fruit were confirmed and it was explained that a set of genes was able to overcome cell wall degradation through the encoding process. In a previous study, UV-C radiation in strawberry fruit also maintained higher firmness and delayed softening due to the presence of a set of genes encoding for proteins and enzymes involved in cell wall degradation [27; 124]. UV-C exposed fresh-cut melon at 1.18 \(\times\) 103 mW\(\cdot\)cm\({}^{-2}\) caused a greater firmness during storage that is related to the accumulation of peroxidase enzyme [125]. This enzyme, as discussed in the previous section, is responsible for creating a barrier between the cell wall and the pathogen, reducing softening and enhancing firmness.