## 3 Results and Discussion
### Comparative Analysis of Volatiles Between Fresh and Frozen PJs  
The volatiles of different frozen PJs (\(-\)20 \({}^{\circ}\)C, \(-\)40 \({}^{\circ}\)C, \(-\)80 \({}^{\circ}\)C) were analyzed and compared by HS-SPME-GC-MS, with the fresh juice sample FPJ0 as the control. A total of 34 volatiles were determined, including 7 terpenes, 7 aldehydes, 15 alcohols, 2 ketones, 2 esters, and 1 acid. Figure 2 shows the total contents of each group for the fresh and frozen PJs. As indicated, alcohols exhibited the highest contents (60.94-91.13 \(\upmu\)g/kg), followed by aldehydes (1.90-3.48 \(\upmu\)g/kg) and terpenes (0.28-3.32 \(\upmu\)g/kg). This finding was similar to the previously reported data [25], which identified alcohols, aldehydes, and terpenes as the crucial volatiles in PJ. As shown in Figure 2, these characteristic volatiles of fresh PJs, mainly referring to alcohols and terpenes, were significantly reduced in the frozen samples. A similar declining trend was observed for acids. Conversely, the total contents of aldehydes, ketones, and esters increased remarkably after the freezing process. A detailed comparison of the major volatile groups considering the fresh and frozen PJs is presented below. Alcohols, as the predominant contributors to PJ flavor, were derived from the oxidation of linoleic acid, and linolenic acid by lipoxygenase (LOX) [19; 26]. As shown in Figure 2, alcohols suffered a decrease after the freezing process, ranging from 91.13 \(\upmu\)g/kg in FPJ0 to 60.94 \(\upmu\)g/kg, 75.66 \(\upmu\)g/kg, and 72.39 \(\upmu\)g/kg in the three frozen samples (\(-\)20, \(-\)40, and \(-\)80 \({}^{\circ}\)C, respectively). Among these, two C6 alcohols (hexanol and (Z)-3-hexen-1-ol) that imparted the fruity, floral, and grassy odor [27] were found in FPJ0 at relatively high levels of 67.76 \(\pm\) 0.55 \(\upmu\)g/kg and 20.45 \(\pm\) 0.11 \(\upmu\)g/kg, respectively (Table 2). However, these two compounds decreased significantly in the frozen samples and fluctuated remarkably as the frozen temperatures decreased. Linalool, reported as a pivotal contributor to the \"floral\" aroma of pomeranate [19], also exhibited a similar decrease in frozen samples (\(-\)20 \({}^{\circ}\)C, \(-\)40 \({}^{\circ}\)C, and \(-\)80 \({}^{\circ}\)C). Conversely, some terpene alcohols, such as terpinen-4-ol and \(\upalpha\)-terpineol, showed an increasing trend following the freezing process. This may be attributed to the degradation of terpenes into terpinen-4-ol and \(\upalpha\)-terpineol through acid-catalyzed and oxidation reactions [28; 29]. Notably, \(\upalpha\)-terpineol seemed to be more easily  
Figure 1: Aroma profiles of 1 fresh and 3 frozen-treated PJs, assessed by quantitative sensory descriptive analysis. “***”, extremely significant (\(\uprho<\) 0.001). formed at relatively low temperatures. As reported, this compound generally produced musty, stale, or piney notes [30]. The higher amounts of this compound in frozen samples possibly imparted an off-flavor in PJs. In total, seven aldehydes were identified in the fresh and frozen PJ samples, and most of their levels in the frozen samples were remarkably higher than those in the fresh FPJ0. This increase in aldehyde content following freezing treatment aligned with the findings of [PERSON] et al. [24], who reported comparable aldehyde accumulation patterns in frozen during pure. Hexanal, a C6 aldehyde responsible for \"green\" and \"grass\" odors [31], was found in FPJ0 at a relatively low concentration of 1.07 \(\pm\) 0.06 \(\upmu\)g/kg, while frozen-treated samples (FPJ\({}_{-}\)-20 \({}^{\circ}\)C, FPJ\({}_{-}\)-40 \({}^{\circ}\)C, and FPJ\({}_{--}\)80 \({}^{\circ}\)C) exhibited higher contents, with the highest being in FPJ\({}_{--}\)20 \({}^{\circ}\)C (3.03 \(\pm\) 0.10 \(\upmu\)g/kg), followed by 2.67 \(\pm\) 0.12 and 2.10 \(\pm\) 0.03 \(\upmu\)g/kg in FPJ\({}_{--}\)40 \({}^{\circ}\)C and FPJ\({}_{--}\)80 \({}^{\circ}\)C, respectively. Octanal and nonanal levels in the frozen samples were also higher than in FPJ0.