## Results and Discussion
### Volatilome of Apples after Storage
The formation of volatiles is on the one hand depending on the activity of the enzymes but on the other hand on the availability of the precursors that are in most cases not odor-active. Based on the results obtained from the analysis of the browning and the juice content, we assume that physiological disorders take place in RA apples after a six months storage period (Section 3.1). The observed discrepancy between primary and secondary aroma compounds in RA-stored Crimson Crisp apples suggests the conclusion that these physiological disorders might make non-volatile precursors better available for the formation of secondary aroma compounds. However, this assumption requires future investigation. The major trend throughout all compound classes, particularly of alcohols and esters, is the presence of highest amounts of volatiles after RA storage and the lowest amounts of volatiles after MCP storage. The only exception is ketones, which show a contrary behavior. This behavior of increasing ketone concentrations compared to fresh fruits corresponds to previous observations made from Golden Delicious and Delicious apples after MCP storage over a period of one month [58]. However, although ketones show a general three-to-four-fold increase in CA and MCP storage, their impact on the overall flavor is expected to be negligible as their concentrations are low. Aldehydes in general are less affected by the storage conditions; their relative concentrations stayed more or less constant with varying relative amounts between 96 and 127% in secondary volatiles. Again, RA storage showed the highest amounts of aldehydes. Aldehydes are final reaction products of fatty acid degradation following the lipoxygenase (LOX) pathway. A reduced LOX activity as the reason for lowered aldehyde concentrations in Galaxy apples was reported in the literatures [55]. A mixed behavior in dependence of the storage conditions was observed for alcohols. While we observed a general decrease in the overall alcohol concentrations in the order of fresh fruits > RA > CA > MCP for primary aroma compounds, we could observe a reduction of the overall quantities of alcohols in secondary aroma compounds from fresh fruits to CA storage by 42% and 80% in MCP storage, while the total amount of alcohols as part of the secondary aroma compounds increased by 53% in RA storage. Enzyme systems that are involved in the formation of straight chain alcohols are lipoxygenase (LOX) and alcohol dehydrogenase (ADH). Several groups reported a reduced activity of the enzyme ACC (1-aminocyclopropane-1-carboxylate) oxidase depending on the storage condition in various apple varieties with MCP application being most effective [57; 59; 60]. ACC oxidase catalyzes the last step within the ethylene biosynthesis pathway and may be used as a measure for the reduction of the autocatalytic ripening processes. The observed reduction in alcohol concentrations in dependence of the storage conditions in this study in Crimson Crisp apples indicate this reduction in ACC oxidase activity. Our findings which show that alcohols from primary aroma compounds follow the described trend, but not the alcohols determined as part of the secondary aroma compounds again indicate that in addition to the enzyme activities, structural changes occur in Crimson Crisp apples in the course of long-term RA storage making non-volatile precursors better available. It is also noteworthy, that the two branched-chain alcohols 2-methylbutanol and 2-methyl-2-buten-1-ol did not follow the trend that was reported for straight-chain alcohols. No clear trend in concentrations can be seen for these compounds in relation to the storage conditions. In contrast to straight-chain alcohols, which are degradation products from fatty acids, branched-chain alcohols are formed by the degradation of the corresponding amino acids and the activity of the enzyme branched-chain amino acid transaminase (BCAT).