## 3 Results and Discussion
### Up-Scaling to the Decon-Box  
Essentially, up-scaling was demonstrated by building a larger facility to meet industrial requirements during commercial apple processing. However, the up-scaling step also includes an advanced process management, which offers some advantages in the PPA treatment. Since PPA is heavier than air, the treatment of the large-scale demonstrator was planned as an immersion process. First, of course, the batch size and number per unit time can be increased significantly. Thanks to the open chamber system, several treatment steps can be carried out in parallel. It gives a time-saving component, since the entire process with all sub-steps does not have to be completed first before a new one is started, as is the case in the tumbler. For instance, a batch of apples that has been treated already with PPA can now enter a rinsing step without any delay. In parallel, a subsequent batch is being treated with PPA without further delays. Additionally, the process management also saves energy. In our experimental set-up in the laboratory, the tumbler has to be PPA-evacuated after every treatment. In contrast, the immersive approach used on the demonstrator saves the PPA after every treatment and can be re-used until the active components of the gas are consumed. The antimicrobial potential of a PPA treatment have been observed for various food-stuff or surfaces [8; 43]. However, also plasma-based post-processing of peanuts has been applied on a lab scale and showed promising results [44]. The vast number of studies prove the growing acceptance of plasma-based methods. Nevertheless, although they are not statistically significant and suffering from high error bars, we interpret the results as promising, since the results appeared to be highly reproducible. [PERSON] found comparable results [45]. A pilot study with artificially inoculated apples followed as a proof of concept of the Decon-Box (Figure 6). Figure 5: (**a**) Results for the native bacterial load on the apple surface investigated under lab-scaled conditions. The picture shows the survivors after a PPA treatment of apples. ; (**b**) That picture shows the reduction factors (RF) obtained after a lab-scaled PPA treatment. All experiments with \(n=3\). Figure 6: Cont. Figure 6a shows the time-dependent growth of _P. fluorescens_ recovered from the inoculated apples after PPA treatment after selected storage days. These results were compared with an untreated reference. Therefore, untreated apples were carried throughout the experiment and batch-sampled along with the treated apples for the selected storage days. The CFU/mL is lower in the treated apples than in the untreated reference apples. Figure 6b shows the growth of _P. maliorticis_ recovered from the inoculated apples after PPA treatment for selected storage days. These results are compared with those for untreated apples similar to the experiments with _P. fluorescens_. The reference varies less than in Figure 6 (only exception on day 8), but the apples were also less effectively inoculated (\(\sim\)10\({}^{8}\) CFU/mL for _P. fluorescens_ and \(\sim\)10\({}^{6}\) CFU/mL for _P. maliorticis_). Treatment of the inoculated apples in Figure 6b shows virtually no reduction compared to the untreated reference or compared to the results in Figure 6a. Figure 6c shows the RF for the treatment of apples inoculated with _P. fluorescens_ and _P. maliorticis_, and the difference between the two treatments is even more pronounced. The RF for the _P. fluorescens_ treatment ranges from 1 log\({}_{10}\)-level (day 10) up to \(\sim\)4 log\({}_{10}\)-level (day 1). This result shows promising tendencies for the bacterial reduction on the apple surface. The treatment of _P. maliorticis_ resulted in no reduction, and therefore further testing on the PPA efficiency on fungi had to be done, since most apple diseases are caused by fungi like the Blue Mold (_Penicillium expansum_). However, the results in Figure 6a-c cannot be properly tested statistically due to lack of sufficient replicates.