## Results and Discussion
### Quality Attributes of Stored Apples
Small changes in the sugar content, which is directly correlated to the TSS content, upon storage were also reported in previous studies [46]. However, it is noteworthy that, in general, TSS show minor, for CA and MCP storage not statistically significant, decrease in Crimson Crisp apples during storage, while it reportedly increases during storage of other cultivars, among them the well-known varieties Golden Delicious and Pink Lady [47; 48]. A decrease in fruit firmness can generally be expected during storage of apples [49]; however, the impact is reportedly cultivar dependent [50]. This makes the evaluation for each cultivar necessary as the firmness is considered a good parameter to predict mealiness in apples [51]. We observed a strong decline in FF after four and six months for RA storage. Values of 6.1 and 6.2 kg/cm\({}^{2}\) were reached, which is a significant difference to both the fresh samples and fruits stored under controlled atmosphere. No statistically significant differences in firmness were observed for Crimson Crisp apples neither stored under CA atmosphere nor under CA conditions with 1-MCP application. The observed, although not significant, changes in MCP storage are most probably due the natural variability of the fruits. Titratable acidity reportedly decreases during storage of apples which, in general, has strong impact on the sensory properties of the fruits [52]. This behavior was also observed for stored Crimson Crisp apples. After six months of storage time, in RA-stored apples TA decreased to only approximately 50% compared to fresh apples, reaching a value of only 8.8 g malic acid equiv./L. In comparison to RA apples, CA and MCP apples showed smaller decreases in acidity over the observed storage period. TA loss in CA-stored fruits was approximately 40%, while MCP-stored fruits still contained higher amounts of organic acids (~20% loss). The observed small decrease in TA of MCP-stored apples corresponded to the expectations, since the conversion of organic acids to other products is mainly associated with higher respiration rates [53]. The juice content (JC) was analyzed to evaluate possible effects on further processing of this cultivar. Furthermore, the JC also reflects the juiciness of the fruits which is an important sensory aspect for consumers upon consumption. We observed a high decrease of JC after four and six months of storage in RA facilities. The juice yield dropped by almost 50% under RA storage. Interestingly, storage longer than four months did not further decrease the JC value in RA-stored fruits. Compared to the fresh apples, samples from CA and MCP storage only showed differences of <10% in the juice content. This behavior might indicate disorders in RA apples leading to JC loss, even though the fruit weight did not show significant difference. Browning of the flesh and the core housing represents a fruit characteristic that is directly perceived by the consumers and is, thus, of high relevance, even though internal browning disorders are not yet completely understood [29; 54]. The results of this study demonstrate that Crimson Crisp apples are not prone to browning of the apple tissue and the core when stored under a controlled atmosphere. When stored under RA conditions, no browning was observed after four months of storage. However, approximately one-quarter of RA stored apples were affected after a period of six months.