# UV Light Application as a Mean for Disinfection Applied in the Dairy Industry
## 3 Inactivation Dose  
The key processing factors in designing a UV-C treatment system are UV dosage, exposure time, Reynold's number, i.e., turbulence and UV transmittance of the liquid food [12]. Disinfection, not sterilization, is a process of removing bacteria from packaging materials [24] either by killing or inactivating microorganisms by damaging nucleic acids and disrupting their DNA, making them incapable of performing essential cellular functions. The systems of surface disinfection are used to eliminate microbial counts on yogurt, milk, butter, and other dairy goods packaging, such as tubs, bottles, containers, lids, and foils. Spoilage microorganisms are removed by UV irradiation of the surfaces prior to filling, such treatment increases the shelf life of the product and lowers the risk of contamination [26]. Ultraviolet radiation with wavelengths of 254 nm has higher energy content than the sun's terrestrial UV light. The DNA of the microorganisms is destroyed by UV light, which transmits a particularly short wavelength. The inactivation time of viruses is about a few seconds and bacteria, yeasts, and fungi are killed in an environmentally friendly way without the use of chemicals. The lethal dose of UV radiation, which can be defined as the dose at which the cells can no longer sustain their metabolism or multiply, is already defined for a wide range of microorganisms. The lethal dose for various foodborne pathogens is distinctly high due to the cell wall structure. As a result, bacteria with a relatively thin cell wall that can only marginally block UV radiation, such as _Salmonella_ and _E. coli_, are highly susceptible and are easily killed. Mold spores, on the other hand, have a thick cell wall that can also be pigmented to shield them from UV radiation and in that case, a UV dose 10 to 100 times higher is used to destroy them [24]. The influence of UV-C (254 nm) on the survival of distinct vegetative bacteria and selected spores is shown in Table 1. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Microorganism** & **F\({}_{-1\text{log}}\) (/m\({}^{3}\))** & **F\({}_{-4\text{log}}\) (/m\({}^{3}\))** & **Reference** \\ \hline \hline Backili & & & \\ \hline Vegetative: _B. anthrac_ & 12–45 & 26–110 & [27; 28] \\ \hline _B. megaterium_ & 56 & - & [29] \\ \hline _B. paraturbusus_ & 32 & - & [27] \\ \hline _B. subtilis_ & 40–60 & - & [30; 31] \\ \hline Spores: _B. anthrac_ & 275 & 620 & [32] \\ \hline _B. megaterium_ & 290 & 600 & [29] \\ \hline _B. subtilis_ & 260 & 600 & [32; 33; 34] \\ \hline Other vegetative microorganisms & & & \\ \hline _Burkholderia cpuctai_ & 31 & 92 & [35] \\ \hline _Burkholderia pesundulla_ & 44 & 130 & [36] \\ \hline _Campylobacter jejuni_ & 11 & 21 & [37] \\ \hline _Citroductor freundii_ & - & 80 & [38] \\ \hline _Coryobacterium diptheriae_ & 34 & - & [27] \\ \hline _Eberthilita typosa_ & 21 & - & [27] \\ \hline _Enterobacter cloace_ & - & 100 & [38] \\ \hline _Enterocilia facetium_ & - & 170 & [38] \\ \hline _Escherichia coli_ & 20–40 & 50–110 & [27; 37] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: UV-C lethal fluence (F) for varying levels of bacterial survival [14]. Most bacteria's sensitivity reports are within a factor of two between various investigations, except for _Y. enterocolitic_, for which variability by a factor of three was observed. The survival of vegetative bacteria had sensitivity ranging from 11 to 80 J/m\({}^{2}\) for a 1 log and 25-200 J/m\({}^{2}\) for a 4 log inactivation respectively [14]. Furthermore, bacterial inactivation by UV treatment is based on the organism's species, age, initial bacterial load, and spore presence. Bacteria that are Gram-negative, such as _Pseudomonas_ and _Escherichia_, are more vulnerable to UV radiation than Gram-positive bacteria (_Bacillus_ and _Staphylococcus_). The optimal time of UV treatment for inactivation of vegetative bacterial cells is during the early lag period, as the bacteria are more resistant to UV light before successful cell division.