## 3 Results
### Emission of Key Alcohols and Aldehydes  
Alcohols in the GD apples were mainly 1-hexanol, 1-butanol, 2-methyl-1-butanol, and 1-octanol (Supplementary Tables S2-S4). The content of alcohols in both the 2 kPa O\({}_{2}\) and air groups initially increased and then gradually decreased during storage (Figure 3). During early storage, the apples stored under 2 kPa O\({}_{2}\) had a lower alcohol content than the air-stored fruit (Figure 3). However, on day 56, for both Flesh1 and Flesh2, the alcohol content in the 2 kPa O\({}_{2}\)-stored fruit increased and was even higher than that in the air-stored fruit (Figure 3A). Interestingly, on day 56 + 23 of the shelf-life period, the total alcohol content of both Flesh1 and Flesh2 in the 2 kPa O\({}_{2}\) group became lower than that in the air group (Figure 3A), suggesting a low recovery capability of alcohols in apple flesh tissue after 2 kPa O\({}_{2}\) storage. The flesh tissue generally had higher alcohol levels than did skin tissue in the apples (Figure 3). On day 56 + 44 of the shelf-life period, higher alcohol levels were still observed in Flesh2 compared with Skin and Flesh1 (Figure 3A). As an abundant alcohol in the GD apple, 1-hexanol showed a similar trend in total alcohol content (Figure 3B, Supplementary Tables S2-S4). In addition, during the shelf-life period, the 1-butanol produced in Flesh1 of the 2 kPa O\({}_{2}\)-stored fruit was also found to be at a lower level compared with that of the air group (Supplementary Tables S2-S4). The aldehydes (Z)-2-heptenal, nonanal, (E)-2-octenal, hexanal, and (E)-2-hexenal, were detected in GD apple tissues (Supplementary Tables S2-S4). The hexanal and (E)-2-hexenal, related to the 'green apple' flavor, accounted for more than 95% of aldehydes in the GD apples (Supplementary Tables S2-S4). Total aldehyde had relatively higher levels in Skin but were lower in Flesh2 (Figure 3C). During early storage, the hexanal content in the skin of 2 kPa O\({}_{2}\)-stored apples was higher, but the (E)-2-hexenal content was lower than that in the air group (Figure 3D,E). However, for Flesh1 on day 14 of storage, the levels of both hexanal and (E)-2-hexenal in apples stored under low oxygen were higher than those in air-stored fruit (Figure 3D,E), which agreed with previous research on 'Fuji' and 'Gala' apples [21]. Moreover, on day 56 + 23 of the shelf-life period, the aldehyde content in Flesh1 of the 2 kPa O\({}_{2}\)-stored apples was also higher than that in the air group (Figure 3C). Figure 2: Key ester content in skin and flesh of ‘Golden Delicious’ apple fruit during 56-day storage under 2 kPa O\({}_{2}\) + 98 kPa N\({}_{2}\) at 4 \({}^{\circ}\)C and subsequent 44-day shelf life at 20 \({}^{\circ}\)C. The contents of total esters, butyl acetate, hexyl acetate, butyl butyrate and 2-methylbutyl acetate are shown in (**A\({}_{1}\)**–**A\({}_{3}\)**, **B\({}_{1}\)**–**B\({}_{3}\)**, **C\({}_{1}\)**–**C\({}_{3}\)**, **D\({}_{1}\)**–**D\({}_{3}\)** and **E\({}_{1}\)**–**E\({}_{3}\)**), respectively. Air represents apple fruit stored in air; 2 kPa O\({}_{2}\) represents fruit stored under 2 kPa O\({}_{2}\) + 98 kPa N\({}_{2}\). Skin indicates tissue obtained 0\(-\)0.1 mm of top pericarp; flesh1 and flesh 2 indicate flesh tissues obtained, respectively, 0.1\(-\)1.0 cm and 2.0\(-\)3.0 cm below the exocarp. Bars indicate standard deviation for each mean value from at least three replicates. Asterisks indicate significant difference between air-stored and 2 kPa O\({}_{2}\)-stored fruit at \(p<0.05\) ([PERSON]’s multiple range test). Figure 3: Key alcohol and aldehyde content in skin and flesh of ‘Golden Delicious’ apple fruit during 56-day storage under 2 kPa O\({}_{2}\) + 98 kPa N\({}_{2}\) at 4 \({}^{\circ}\)C and subsequent 44-day shelf life at 20 \({}^{\circ}\)C. The contents of total alcohols and 1-hexanol, are shown in (**A\({}_{1}\)**-**A\({}_{3}\)**, **B\({}_{1}\)**-**B\({}_{3}\)**), respectively.