## 3 Discussion  
Browning can quickly occur on fresh-cut apples, seriously affecting their sensory quality and nutritional value [26]. The mechanical damage from fresh-cutting induces a large amount of ROS in apples. Excessive ROS can attack cell membrane lipids, leading to increased membrane lipid peroxidation, increased membrane permeability, and destruction of the phenol-phenolase regional structure, thereby increasing enzymatic browning [27]. Browning occurs after fresh-cutting, but the browning degree of the T2 treatment is lower than that of other treatments. Fruit firmness is an important indicator of fruit and vegetable storage quality. Low firmness in fresh-cut apples affects their commercial value [28]. Cell wall modification and middle lamella polysaccharide dissolution are thought to be the main factors in the decrease in pulp firmness [29]. In apple, firmness and storability decline, storage life is shortened, and quality is reduced [30]. Sorbitol-chelated calcium treatment effectively reduces enzymatic browning and preserves firmness in fresh-cut apples by stabilizing cellular membranes through calcium-mediated pectin cross-linking. Simultaneously, calcium ions reinforce cell wall integrity by forming Ca\({}^{2+}\)-pectate bridges, delaying polysaccharide dissolution and enzymatic degradation. This mechanism stabilizes cell wall structure, thereby extending shelf life and maintaining sensory and commercial quality. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **Volatile** & **Esters** & **Alcohols** & **Aldehyde** & **_AAT1_ & **_AAT2_ & **_LOX_** & **_HPL_** & **_ADH_** \\ \hline Volatile & \(1\) & & & & & & & \\ Esters & 0.884 * & \(1\) & & & & & & \\ Alcohols & 0.909 * & 0.735 & \(1\) & & & & & \\ Aldehyde & 0.588 & 0.554 & 0.297 & \(1\) & & & & \\ _AAT1_ & 0.898 * & 0.921 * & 0.777 & 0.740 & \(1\) & & & \\ _AAT2_ & 0.825 & 0.934 * & 0.672 & 0.736 & 0.983 ** & \(1\) & & \\ _LOX_ & 0.874 & 0.830 & 0.671 & 0.895 * & 0.950 * & 0.921 * & \(1\) & \\ _HPL_ & 0.605 & 0.555 & 0.341 & 0.997 ** & 0.762 & 0.750 & 0.906 * & \(1\) & \\ _ADH_ & 0.783 & 0.848 & 0.668 & 0.770 & 0.976 ** & 0.978 ** & 0.923 * & 0.797 & \(1\) \\ \hline \hline \end{tabular} Note.* The significant level, \(p<0.05\); ** The significant level, \(p<0.01\).  
\end{table} 
Table 4: The correlation between aroma substances and related genes. Figure 7: Heatmap of correlation analysis between volatile matter and related gene expression in apple during storage. The change in ultrastructural structure is an important feature of fruit ripening and aging, reflecting the physiological state of the fruit. As fruit matures, the ultrastructural function of tissue cells weakens or is lost, accelerating fruit senescence and spoilage [31]. Studies have shown that, during storage, fruit cell walls, mitochondria, and starch granules degrade, damaging the integrity of organelles and membrane systems [32]. The TEM results showed that the cell walls of each treatment were degraded, cell gaps became larger, and ultrastructural integrity was reduced. However, the sorbitol-chelated calcium treatment was superior to other treatments, showing significant inhibition of ultrastructural damage after fresh-cutting. This may be because sorbitol-chelated calcium reduced the decomposition of pectin in fresh-cut apples during storage, so that apples accumulated more pectin and other nutrients, providing better hardness, density, and other texture characteristics and maintaining the integrity of the ultrastructure of apples after fresh-cutting. Fresh-cut apples are typically contaminated by various microorganisms during spoilage, mainly fungi and bacteria. _Penicillium_, _Aspergillus_, and _Alternaria_ can cause black mold spots on apples and produce harmful substances. The microbial load of fresh-cut fruits is related to cultivation, harvesting, and processing [33]. Most microorganisms have difficulty penetrating intact fruits, but they can colonize tissues and grow when the protective layer is damaged, leading to spoilage of fresh-cut fruits [34].