## 3 Results  
Impact of One Ozone Treatment per Day on Odour-Active Compounds, Total Titratable Acidity, Weight Loss, and Mould Growth  
The impact of one ozone treatment with 81 ppm ozone for 20 min per day on different quality parameters during the storage of oranges and bananas was tested in a first experiment. The quantified odorants were selected based on the existing literature on key odorants in oranges, freshly pressed orange juice [21; 22; 23], and bananas [24; 25]. The odorant concentrations in the bananas during storage without and with ozone treatment are displayed in Figure 1 and Table S3. The analyses included eight important banana odorants, with mainly acetates and butanoates as important fruity-smelling esters in bananas [24]. With concentrations surpassing their odour threshold at the latest on day 2, this research confirms the importance of most of the quantified odorants for the banana odour. Especially high concentrations were found for 3-methylbutyl acetate and 3-methylbutan-1-ol. Only 3-methylbutyl 3-methylbutanoate showed concentrations below its odour threshold until day 9, and ethyl 3-methylbutanoate was only detectable from day 4 onwards. In the summary of all odorants, no significant differences were found between the samples treated with ozone and the control samples for most odorants, with the exception of 3-methylbutan-1-ol. Its concentration on day 9 was significantly higher in the ozone-treated sample, whereas its concentration after 11 days was significantly higher in the control sample. Even though the differences were significant, no clear trend was observed. Small and non-significant differences between the two groups in the concentrations of the other odorants did not indicate a trend regarding a possible influence of the ozone treatment. 2-Methylpropyl butanoate showed mostly higher concentrations in the control samples compared to the ozone-treated samples, except for day 7. In contrast, the ethyl 3-methylbutanoate and pentan-2-yl acetate concentrations were slightly higher in the ozone-treated samples on most days. Generally, high standard deviations were observed for most samples, independent of the storage type and day. The broad range of odorant concentrations in the samples indicated high natural variations in the bananas. As demonstrated by the non-significance of most differences, the natural variations had a greater influence on the odorant concentrations than the storage type. Figure 1: Mean concentrations of the selected odorants with standard deviations in bananas during storage without (control) and with ozone treatment once a day. Different letters after the value indicate a significant difference between the samples for the compound. In addition to the natural variations in the fruits, the storage time had a higher impact on the odorant concentrations than the storage type. Most odorants showed low concentrations at the beginning of the storage and an increase over time. A very steep increase from day 0 to day 2 was observed for pentan-2-yl acetate, 3-methylbutyl acetate, 2-methylpropyl butanoate, and 3-methylbutyl butanoate. 3-Methylbutyl 3-methylbutanoate showed a steep increase from day 9 to day 11 and reached a concentration above its odour threshold only on day 11. A slower increase rate was observed for 3-methylbutan-1-ol and ethyl butanoate. The formation of odorants during storage is part of the ripening process of the bananas, which continues after harvesting [4]. Especially, esters are known to increase during banana ripening [26; 27; 28; 29], and 3-methylbutan-1-ol was reported to increase during ripening until a certain ethanol level is reached [29]. [PERSON] et al. [29] observed a decrease in esters at a certain time of storage, which was highly dependent on the storage temperature. This study observed a decreasing effect at the end of storage for 3-methylbutyl acetate and pentan-2-yl acetate. The same experiment was analogously performed with oranges. The concentrations of the quantified odorants in oranges are displayed in Figure 2 and Table S4.