## 2 Results
### Effects of Different Postharvest Calcium on Metabolomics of Fresh-Cut Apples During Storage  
The PCA score scatter plot of all samples (Figure 4a) showed that the distribution of T2 (sorbitol-chelated calcium) samples was close to that of T1 and T3, indicating similar metabolite composition and content among the three different calcium treatments. However, overall metabolic levels exhibited significant differences. Figure 4b presents a volcano plot of differential metabolites, which visually illustrates the overall distribution of metabolite differences between groups. From the comparison between the T2 group and the T1 group, it can be observed that the number of significantly differential metabolites is 1020, with 587 being upregulated and 433 downregulated. From the comparison between the T2 group and the T3 group, it can be observed that the number of significantly differential metabolites is 964, with 619 being upregulated and 345 downregulated. From the Venn diagram in Figure 4d, it can be observed that 1358 co-expressed metabolites are shared among the three treatments. Between the T2 and T1 groups, 498 differentially expressed metabolites were identified, indicating that the T2 treatment plays a significant role in the accumulation of differential metabolites in fresh-cut apples. To further analyze the impact of T2 treatment versus T1 treatment on metabolite changes and their associated pathways, we conducted an in-depth analysis of the effects of differential metabolites on their respective metabolic pathways. Through comprehensive pathway analysis (including pathway analysis and a KEGG heatmap for T2 vs. T1 groups), we further screened the pathways and identified the three most significantly correlated key pathways: flavonoid biosynthesis, tyrosine metabolism, and isoflavonoid biosynthesis. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Microbial Species** & \multicolumn{3}{c}{**Different Calcium Preparation Treatment Groups**} \\ \cline{2-5}  & **CK** & **T1** & **T2** & **T3** \\ \hline _Penicillium_ & 2.34 \(\pm\) 0.09 a  & 1.89 \(\pm\) 0.08 b  & 1.13 \(\pm\) 0.09 d  & 1.77 \(\pm\) 0.02 c  \\ _Aspergillus_ & 1.43 \(\pm\) 0.06 a  & 1.33 \(\pm\) 0.06 b  & 1.07 \(\pm\) 0.06 c  & 1.12 \(\pm\) 0.04 b  \\ _Alternaria_ & 2.89\(\pm\) 0.11 a  & 1.87 \(\pm\) 0.13 b  & 1.61 \(\pm\) 0.07 c  & 1.76 \(\pm\) 0.04 b  \\ _Ervinia carototovora_ & 4.43 \(\pm\) 0.12 a  & 3.34 \(\pm\) 0.13 b  & 2.97 \(\pm\) 0.15 c  & 3.03 \(\pm\) 0.12 c  \\ Total colonies & 5.68 \(\pm\) 0.18 a  & 4.80 \(\pm\) 0.12 b  & 3.70 \(\pm\) 0.09 d  & 4.19 \(\pm\) 0.13 c  \\ \hline \hline \end{tabular} Note: Different lowercase letters in the same developmental stage are significant differences at \(p\) < 0.05.  
\end{table} 
Table 2: Changes in spoilage microorganisms on the 12 th day after fresh-cutting of apples in different calcium preparation treatment groups (lg CFU/g\({}^{-1}\)). Figure 4: Effects of sorbitol-related calcium on metabolomics of fresh-cut apples during storage. (**a**) Principal component analysis, PCA plot. (**b**) Volcano plot of differential metabolites. (**c**) Pathway analysis for T2 vs. T1 groups. (**d**) Venn diagram of differential metabolites. (**e**) KEGG heatmap for T2 vs. T1 groups. Effects of Different Calcium Treatments After Harvest on Aroma and Volatile Components of Fruit During Storage  
We further investigated the changes in metabolites within the three significantly altered metabolic pathways identified by metabolomics in fresh-cut apples treated with sorbitol-related calcium. The qualitative and quantitative analysis of volatile substances in four apple treatments by GC-MS revealed that the main components were esters, alcohols, and aldehydes. During storage, the contents of total aroma substances, esters, and alcohols initially increased and then decreased (Figure 5 and Table 3).