## 2 Results and Discussion
### Changes in the Composition of Volatile Compounds in Strawberries  
Figure 2 shows the sum of the volatile compounds of the strawberries. Before storage (0 d), the sum of the volatiles in bright-red strawberries (B0h, 3787 \(\upmu\)g/kg) was 1.24-fold higher than that of the half-red strawberries (H0h, 3044 \(\upmu\)g/kg). These findings agree with those of previous studies, showing that the sum of the volatiles in 'Cigaline' strawberries increased during maturity [25]. After 9 d of storage, the volatile concentrations of strawberries used as control increased to a greater extent (B9D, 8186 \(\upmu\)g/kg; H9D, 10,198 \(\upmu\)g/kg) than those of CO\({}_{2}\)-treated strawberries (BT9D, 5130 \(\upmu\)g/kg; HT9D, 5480 \(\upmu\)g/kg). Thus, short-term CO\({}_{2}\) treatment of strawberries at two ripening stages may inhibit the production of volatiles during 9 d of storage. The MANOVA results showed that CO\({}_{2}\) treatment and storage time affected the concentrations of the total volatiles (i.e., sum of volatiles) (\(p<0.001\)), as shown in Supplementary Materials, Table S1. The volatile composition of strawberries varied with maturity. For example, bright-red strawberries showed a higher ester/aldehyde ratio compared to that of half-red strawberries at day 0. After 9 d of storage, the aldehyde contents of half-red strawberries (H9D) and bright-red strawberries (B9D) decreased to 78% and 71%, respectively, compared to that at day 0. However, the ester contents of H9D and B9D increased 3.0-fold and 1.8-fold, respectively, compared to that at day 0. The ester content of CO\({}_{2}\)-treated half-red strawberries (HT9D) was 68.5% that of the total volatiles. This value was similar to that of the half-red. Figure 2: Sum of volatile compounds in (**A**) half-red and (**B**) bright-red strawberries stored at 10 \({}^{\circ}\)C for 9 d (H: half-red, B: bright-red, T: CO\({}_{2}\)-treated, h: hours, D: days). Lowercase and capital letters indicate significant difference for half-red and bright-red strawberries, respectively (\(p<0.05\)). The relative concentrations of individual volatile compounds in the control and CO2-treated strawberries at two ripening stages--(A) half-red and (B) bright-red--during storage are shown in Tables 2 and 3. The relative concentrations of characteristic volatile compounds of the strawberries are shown in Figure 3. The concentration of each volatile compound was described as the relative concentration of the appropriate internal standard. In half-red strawberries, the hexanal concentration significantly decreased from 217 ug/kg (H0h) to 41 ug/kg (HT9D) and 56 ug/kg (H9D) after 9 d in storage (\(p<0.05\)). Furthermore, the 2-hexanal concentrations significantly decreased from 975 ug/kg (H0h) to 413 ug/kg (H9D) and 333 ug/kg (HT9D). No significant difference was observed in the hexanal and 2-hexanal concentrations between H9D and HT9D (\(p>0.05\)). The hexanal concentrations of stored bright-red strawberries (B9D, 25 ug/kg; BT9D, 48 ug/kg) decreased compared to those in fresh bright-red strawberries (B0h, 160 ug/kg). Furthermore, the 2-hexanal concentrations of stored bright-red strawberries (B9D, 164 ug/kg; BT9D, 308 ug/kg) decreased compared to those of fresh half-red strawberries (B0h, 871 ug/kg). The 2-hexanal concentration of BT9D was significantly higher than that of B9D (\(p<0.05\)). A previous study reported that the concentrations of hexanal and 2-hexanal, the characteristic volatile compounds responsible for the fresh and fruity odor of fresh strawberries, decreased during storage [28]. Hexanal may help delay the ripening process through the inactivation of phospholipase D, membrane lipid-degrading enzymes, and downstream oxidative signaling, and enhance shelf-life, as shown in mango fruits [29]. Moreover, hexanal may help reduce postharvest deterioration by preventing the growth of microorganism and fungi [30]. Interestingly, postharvest hexanal treatment on 'Rubygem' strawberries increased the alcohol percentage of the fruit at the end of their shelf-life [15].