## 2 Influence of UV-C on the Physical and Mechanical Properties of Different Crops
### Physical Properties  
With a specific focus in food characterization, textural profile analysis (TPA) offers comprehensive properties important to the acceptability of a product by the end user. A wide set of parameters traced from TPA analysis includes hardness, cohesiveness, viscosity, elasticity (springiness), adhesiveness, resilience, brittleness (fracturability), chewiness, and gumminess. This is one of the most important parameters as far as the UV-C stimulation is concerned with the cell physiology. The properties of firmness, hardness, and change in mass are critically assessed in this review as they are greatly influenced by the anatomy of the plant tissue, the strength of the cell wall, and ultimately other mechanical properties. It is one of the most important parameters when it comes to UV-C stimulation and cell physiology [57]. The firmness of bell pepper fruit treated at 0.25 kJ\(\cdot\)m\({}^{-2}\) and its control sample significantly dropped at the initial storage period, but after seven days of storage the UV-C treated sample was found to be firmer than the control. A weight loss experiment in the same fruit resulted in lower weight loss in the treated sample [58]. An experiment on the UV-C treated in green asparagus confirmed an appreciable increment in tissue toughness and a significant increase in cutting energy (sheer force) even at a lower UV-C dose of 1 kJ\(\cdot\)m\({}^{-2}\) and 8 min exposure time [59]. Conversely, a low UV-C dose up to 3.8 kJ\(\cdot\)m\({}^{-2}\) is indicated to have an insignificant change in textural properties [60]. Observations on the fresh-cut melon after UV-C exposure confirms no significant difference in the firmness as a result of UV-C application at 1.2 kJ\(\cdot\)m\({}^{-2}\) followed by storage at 6 \({}^{\circ}\)C [61]. No significant difference was observed among treated and control samples in delaying softening at a lower UV-C dose. The research work on the firmness and weight loss characteristics of UV-C exposed fresh-cut apples were analyzed by different authors and resulted in no significant change in the firmness [62; 63], while a decrease in weight loss by 6% was noted at an exposure time of 1 min and intensity of 1.2 kJ\(\cdot\)m\({}^{-2}\) UV-C [62]. For fruit crops, weight loss is an important parameter as it is associated with dehydration, which significantly determines the commercial value of the fruit. The weight loss of amaranth vegetables treated at a moderate UV-C dose of 1.7 kJ\(\cdot\)m\({}^{-2}\) reduced the weight loss significantly better than the control [64]. The weight loss experiment on different UV-C exposed tomato cultivars, namely \"cherry tomato\" and _Eplida_, showed no effect and reduced weight loss when treated at 3.7 kJ\(\cdot\)m\({}^{-2}\) and 4 kJ\(\cdot\)m\({}^{-2}\), respectively [65; 66]. It was depicted that a lower UV-C dose of up to 4 kJ\(\cdot\)m\({}^{-2}\) has a minor effect on the firmness of tomato [67] and blueberry fruits [68]. The firmness value of different tomato cultivars was enhanced when exposed to UV-C treated in the range of 3 kJ\(\cdot\)m\({}^{-2}\) to 4.2 kJ\(\cdot\)m\({}^{-2}\)[65; 66; 69; 70; 71; 72]. An experiment conducted on the quality parameters of UV-C exposed pineapide at the dose of 4.5 kJ\(\cdot\)m\({}^{-2}\) over the range of 0-90 s and followed by a 10 \({}^{\circ}\)C storage condition was able to retain the firmness properties better than the control samples [73]. Exposure to 7.11 kJ\(\cdot\)m\({}^{2}\) induced higher tissue softening in lettuce and caused the development of abnormal color in cauliflower [74; 75]. Research work on a comparative study of the effect of UV-A and UV-C over the temperature range of 25-100 \({}^{\circ}\)C on oyster mushrooms reported UV-C exposed mushroom samples had a higher increase in loss modulus and loss factor than that of UV-A exposed ones. From the outcome, it was concluded UV-C light had a greater impact on the mechanical properties of oyster mushrooms compared to UV-A light [76].