## 3 Results and Discussion
### Comparative Analysis of Volatiles Between Fresh and Frozen PJs
Most of these compounds were described as having woody and grassy flavor [11; 36]. Consequently, the reduction or absence of these terpen might result in weaker woody and grassy notes in frozen PJ samples. With regard to esters, none were detected in FPJ0. Some certain esters, such as ethyl acetate and ethyl hexanoate, were identified as key contributors to the aroma of pomegranate [25; 37]. However, these specific esters were not detected in FPJ0, possibly due to geographical and cultivar variations. Notably, following frozen storage, hexyl acetate was formed in all frozen samples (FPJ\({}_{--}\)20 \({}^{\circ}\)C, FPJ\({}_{--}\)40 \({}^{\circ}\)C, and FPJ\({}_{--}\)80 \({}^{\circ}\)C), while (\(Z\))-2-hexened-1-ol acetate was only present in FPJ\({}_{--}\)80 \({}^{\circ}\)C, albeit at low concentrations. Similar to esters, ketones, including 6-Methyl-5-hepten-2-one and 2-nonanone, were also more abundant in the frozen samples. 6-Methyl-5-hepten-2-one, a significant contributor to herbaceous and green attributes of fruit [34], exhibited the highest content in FPJ\({}_{--}\)40 \({}^{\circ}\)C, while 2-nonanone, described as having fresh and green notes [5; 38], was only found in frozen samples, with FPJ\({}_{--}\)80 \({}^{\circ}\)C having the highest amount (1.15 \(\pm\) 0.03 \(\mu\)g/kg). In conclusion, the freezing treatment significantly altered the formation of volatile substances in pomegranate juice, with an overall decrease consistent with previous studies on the frozen storage of juice and fruit [6; 39; 40]. Compared to fresh sample FPJ0, the lowest fluctuation in volatiles was found in the FPJ\({}_{--}\)40 \({}^{\circ}\)C and FPJ\({}_{--}\)80 \({}^{\circ}\)C groups. This result was consistent with the QDA (Figure 1), which indicated that the FPJ\({}_{--}\)40 \({}^{\circ}\)C and FPJ\({}_{--}\)80 \({}^{\circ}\)C samples had less loss of aroma intensity, particularly for woody, grassy, fruity, and floral aromas. To explore the volatile differences between the fresh (FPJ0) and frozen PJ juices (FPJ\({}_{--}\)20 \({}^{\circ}\)C, FPJ\({}_{--}\)40 \({}^{\circ}\)C, and FPJ\({}_{--}\)80 \({}^{\circ}\)C), principal component analysis (PCA) and hierarchical cluster analysis (HCA) based on all volatiles were further analyzed (Figure 3). Figure 3A shows the score plot of the PCA, with PC1 (68.0%) and PC2 (17.2%) contributing 85.2% of the total variance. As shown, along PC1, the fresh control sample FPJ0 and the three frozen PJ samples (FPJ\({}_{--}\)20 \({}^{\circ}\)C, FPJ\({}_{--}\)40 \({}^{\circ}\)C, and FPJ\({}_{--}\)80 \({}^{\circ}\)C) are distinctly positioned on either side of the vertical axis. Among the frozen-treated samples, along PC2, three frozen samples are also clustered in different regions. These findings indicate that the volatile profiles of PJs post-freezing were significantly different from those of fresh juice. Figure 3B shows a heatmap of the hierarchical clustering analysis (HCA) based on Euclidean distance metrics. The relative concentrations of volatiles from low to high are represented through a normalized color gradation from a minimum of \(-\)3.00 (white) to a maximum of 3.00 (red). According to the dendrogram, the four PJ samples were clearly divided into two major clusters: FPJ0 was in one group, and FPJ\({}_{--}\)20 \({}^{\circ}\)C, FPJ\({}_{--}\)40 \({}^{\circ}\)C, and FPJ\({}_{--}\)80 \({}^{\circ}\)C were in the other group, which was in accordance with the PCA results (Figure 3A), further indicating that the freezing process has a great impact on the volatile profiles of PJs. In addition, as for volatiles, they could also clearly be divided into two parts (I and II). The volatiles in Part I were relatively more abundant in the frozen samples, with a total of 13 volatiles, of which aldehydes and alcohols accounted for a larger proportion.