## 3 Results and Discussion
### Quality Measurements of Treated Apples  
The quality of produce after a PPA treatment was evaluated based on photographic pictures and texture analysis. Figure 7a summarizes the arithmetic means of all artificially inoculated apples, which underwent PPA treatment. The apples have been compared with their references. Both apples inoculated with _P. fluorescens_ and those inoculated with _P. malicorticis_ show only a variation in their texture that is within the texture variation of their references. Figure 7b depicts the texture analysis of PPA-treated apples in a pilot scaled experiment. Contrary to the lab-scaled experiments, apples treated in the Decon-Box did not undergo an artificial inoculation step. The apples were treated with different treatment times. Based on the collected data, a 20 min and a 30 min PPA treatment did not reveal any statistical meaningful differences in their crispiness. The matrix of PPA-treated apples stays unchanged throughout the whole set of experiments. These findings support our hypothesis that the antimicrobial active compounds stay solely on the surface of the apples, where they adversely influence the growing microflora. Obviously, these compounds do not enter through the lenticels and do not damage the tissue underneath the apple peel. To test the effect of treatment on the storability of organic apples, a control batch and a treated batch of organic apples were observed over a period of 8 weeks (56 days) (Figure 8). As an example, one apple for each of the control and treatment are shown in the following Figure 1 day, 14 days, 7 weeks (49 days), and 8 weeks (56 days) after treatment. The difference between controls and PPA treatment is marginal and shows that the treatment neither causes visible damage to the apples nor influences the coloration of the apples and does not affect their storability. Therefore, it can be considered that the PPA treatment is an adequate solution to improve the storage of apples, since not only the microbial load is reduced (with the exception of _P. malicorticis_ but also the regrowth for _P. fluorescens_ and the native microbial inhabitants on the apple surface is impeded. Another indication of the usefulness of PPA treatment is the scalability of the treatment process, taking advantage of the fact that PPA is heavier than air. Thus, the immersion tank only needs to be enlarged and can then be filled with the heavier PPA. In the case of fruits and vegetables, reactions typically continue to occur even after harvesting [43]. For instance, an apple has to be always considered as a living tissue [44]. Through various different metabolic processes, ripening continues to progress and this contributes to the change in color, in addition to many other phenomena such as the change  
Figure 7: (**a**) Texture measurement of PPA-treated apples on the laboratory scale, which are artificially inoculated with _P. fluorescens_ and _P. malicorticis_. The treated apples have been compared with their untreated counterparts (reference); (**b**) texture measurements of PPA-treated apples in the up-scaled experiments, which were conducted in the Decon-Box. Two different PPA treatment times (20 min and 30 min) are compared with their untreated references. in taste, texture, and aroma. This is caused by the degradation of chlorophyll, which provides a green color impression, to various degradation products such as chromoplasts, which produces a color change towards yellow and red tones [12]. Figure 8: _Cont._  
Regularly, apples undergo a hot-water treatment that improve their storability. This method has been under research for decades [45; 46; 47]. [PERSON] (2018) describe a bacteria reduction due to a hot-water treatment up to three \(\log_{10}\)-steps [12; 13]. This magnitude of reduction is also reached for _P. fluorescens_ after PPA treatment and a storage period up to 25 d. These findings have been underpinned by quality measurements such as the photographic documentation of the stored apples and the measurement of the apple's texture. However, [PERSON] et al.