## Results and Discussion
### Sensory Analysis of Stored Crimson Crisp Apples  
The analysis of the fruit volatilome delivers valuable information about the formation and degradation of volatiles, whether or not they are odor-active. However, to understand the impact on the overall flavor of the fruits, sensory evaluation is required. For the sensory analysis of the stored Crimson Crisp fruits, a trained panel was asked to describe the aroma, texture and overall flavor of the three samples RA, CA and MCP by using 'open-ended questioning' (OEQ) as the sensory technique [41]. The application of this descriptive technique makes it possible to assess data about the stored apples beyond the scope of the predefined CATA analysis for fresh apples that we applied to follow the fruit development during on-tree ripening [33]. OEQ results were visualized as a biplot as a result via correspondence analysis (Figure 3).  
Figure 3: Symmetric plot (axis F1 and F2; 100%) of the correspondence analysis of the open-ended questioning (OEQ) based on Chi-square statistics (\(p<0.05\)). RA = regular air storage, CA = controlled air storage, MCP = controlled air + 1-MCP.  
Figure 2: Principal component analysis (PCA, Pearson correlation) biplot of the volatile compounds (primary aroma compounds) of fresh and stored Crimson Crisp apples (variables) and the storage techniques (observables) calculated with the relative concentrations of the volatiles given in Table 2. Compound names given in quadrant II and III appear in the order of their position from top to bottom of the cluster near the centroid of the biplot. (alc = alcohols; ald = aldehydes; est = esters; ket = ketones, oth = others).  
The symmetric plot, which is a 2-dimenionsal representation of the OEQ results, shows a clear differentiation between the RA apples and the apples stored under CA and MCP along the \(x\)-axis with the principal component F1 explaining 93% of the variability. Furthermore, the results show that RA-stored apples were correlated with a very intense aroma. This is in high accordance with the results obtained from GC-MS analysis of the volatilome (Section 3.2), where compounds such as 1-butanol (medicine, wine, fruit),butyl acetate (pear) and butyl 2-methylbutanoate (fruit, cocoa) showed the highest relative concentrations in the secondary volatilome (odor descriptors [65]). The texture was described as soft, mealy and not juicy. This is in line with our results for firmness, which showed that the firmness and juiciness of RA apples decreased significantly during storage (Section 3.1). The apples were also reported to be overripe and in contrast to the soft pulp, they exhibited a firm apple peel. Both descriptors are relatively less desirable for the choice of table apples [40; 66].  
The results given in Figure 3 also show that apples stored in CA and MCP were very similar to each other as the principal component F2 only counts for approx. 7% of the variance. The descriptors located in quadrants II and III are closely related to both sample sets from CA and MCP storage. Both samples were correlated to ripe, crisp/compact apples. CA and MCP fruits exhibit a balanced sweet-sour ratio and they were perceived as fresh with apple and fruity odor sensations by the sensory panel. Even though F2 only accounts for 7% of the variance, differences were observed between the two apple samples CA and MCP. The fruits stored in CA storage express a higher fruitiness, with a sweet aroma and also have floral and green notes. Although CA apples had the highest TSS content, this is not reflected in the sensory properties of the fruits. In contrast to CA apples, MCP apples do not show expressed fruitiness. The sensory descriptors are dominated by texture attributes (crispness, juiciness, a 'watery' impression). These results correlate well with those obtained from the analytical data--MCP apples showed the lowest concentrations in volatile compounds, whereas the pulp firmness and juiciness were highest among the investigated fruits.