## 3 Results and Discussion
### Effects of the UV Light Source and TiO\({}_{2}\) Photocatalysis on Inactivation of Microorganisms
Combined UV-TiO\({}_{2}\) resulted in slightly more degradation than combined UV for all treatment times, but without a significant difference. The slightly higher inactivation effect of combined UV-TiO\({}_{2}\) can be attributed to the decrease in shadowing effect in UV disinfection process. UV treatment is a conventional method for disinfection of fresh produce, but it has limitations for industrial applications due to the shadowing effect. Microorganisms on rough surfaces or complex matrices of food are difficult to target while using UV light, because target microorganisms on food surfaces must directly face a UV lamp for inactivation [58; 59]. Furthermore, when UV light is commercially applied to fresh produce in a processing line, individual  
Figure 7: Inactivation of microbial contamination on fresh cut carrots using combined UV and combined UV-TiO\({}_{2}\). (**a**) _E. coli_ K12; (**b**) _Saccharomyces cerevisiae_. Bubble water wash (BW) = air bubbling as a control; Combined UV = UVC and VUV; combined UV-TiO\({}_{2}\) = UVC-assisted TiO\({}_{2}\) photocatalytic; and, VUV-assisted TiO\({}_{2}\) photocatalytic treatment. The _N\({}_{0}\) of E. coli_ K12 and _S. cerevisiae_ were in the range of 6.5-8.0 log CFU/cm\({}^{2}\) and 4.3-5.6 log CFU/cm\({}^{2}\), respectively. The results represent the mean of three measurements \(\pm\) standard deviation. object also casts shadow on other objects. In the past decades, research on UV disinfection has focused on hurdle technologies or reactor design, such as water-assisted UV system, to achieve higher inactivation efficacy [60; 61; 62]. In UV-TiO\({}_{2}\) photocatalytic treatment, TiO\({}_{2}\) absorbs the energy of photon under irradiation of UV light. When the energy of photon is higher than the width of the semiconductor's void band (3.2 eV; the UV light with \(\lambda<387.5\) nm), the electron of valence band will transfer to the conduction band. Therefore, the pairs of electron-holes are created in the TiO\({}_{2}\), and the charge will be transferred between electron-hole pairs and adsorbed species (H\({}_{2}\)O, OH-, O\({}_{2}\), other reactants) on the TiO\({}_{2}\), and then photo-oxidation occur. Finally, reactive oxygen species (OH-, HO\({}_{2}\), O\({}_{2}\)-, H\({}_{2}\)O\({}_{2}\)), mainly hydroxyl radicals (OH-), are generated [63]. Hydroxyl radical can cause cell wall disruption and oxidation of cytoplasmic contents, eventually leading to microbial cell death [2; 64; 65]. Hydroxyl radical can reduce the shadow effects of the UV disinfection process, providing a far-reaching antimicrobial impact on bacterial cells [26]. UV-TiO\({}_{2}\) photocatalysis showed higher reduction in the natural microflora populations and inoculated populations of the pathogenic bacteria _E. coli_, _Listeria monocytogenes_, _Staphylococcus aureus_, and _Salmonella Typhimurium_ on iceberg lettuce compared to UV alone and a sodium hypochlorite solution treatment [66]. In this study, tap water was used as wash water to exclude the effects of salts and minerals on microbial inactivation in TiO\({}_{2}\) photocatalytic treatment. For example, in TiO\({}_{2}\) photocatalysis, chloride ions (CI\({}^{-}\)) react with photogenerated holes from valence band of TiO\({}_{2}\) to form chlorine radicals (CI\({}^{-}\)). Chlorine radicals then react with CI\({}^{-}\) and convert into chloride radical anion (Cl\({}_{2}\)\({}^{-}\)) [67]. For this reason, photocatalytic disinfection of bacteria in saline water may be more effective than the plain water. It was also considered that distilled or demineralized water and saline solutions are not suitable for applications to industry due to limitations, such as cost and additional equipment.