## 3 Results and Discussion
### Volatiles Analysis
#### 3.4.2 Changes in Volatiles of HHP-Treated Kiwifruit Pulp Beverage during 40-Day Storage  
Main volatiles of kiwifruit pulp beverage were found to change over 40 days (Figure 7). All volatiles in heat-treated and HHP-treated kiwifruit pulp beverage during storage at 4 \({}^{\circ}\)C for 40 days were shown in Table S1-S3. HHP treatments at 500 MPa/15 min and 600 MPa/15 min showed better effect of characteristic aroma protection due to slight changes in content of hexanal as well as (_E_)-2-hexenal during storage. Nevertheless, the content of hexanal and (_E_)-2-hexenal in heat-treated and the rest of HHP-treated samples indicated reduction with time. In accordance with this result, [PERSON] et al. [54] reported that the levels of hexanal and (_E_)-2-hexenal in Hayward kiwifruit pure declined with time. Similarly, the 1-octen-3-one content decreased during storage and was not detectable in samples processed at 500 MPa for 5-10 min and 600 MPa for 5-10 min on the 40 th day, indicating long term storage resulted in a diminished 1-octen-3-one content. As was shown in Figure 7D, 1-penten-3-one content fluctuated in 40 days while 1-penten-3-one of HHP-treated (500 MPa/15 min) samples was less affected by storage. As a consequence, HHP at 500 MPa for 15 min was positive to preserve 1-penten-3-one in kiwifruit pulp beverage. As seen in Figure 7E, 1-hexanol content increased over 40 days. In study of [PERSON] et al. [55], the same trend was observed in 1-hexanol content of strawberry puree processed at 400 MPa for 20 min during 30 days at 4 \({}^{\circ}\)C. This may due to the residual activity of lipoxygenase [50]. Differences between the 1-hexanol content in samples of different treatments became larger on the 40 th day. Higher content of 1-hexanol was detected in pulp beverage processed at 500 MPa/10 min (16.44%), which was even bigger than initial 1-hexanol content of untreated samples (15.07%). It can be seen in Figure 7F that the 1-octen-3-ol content gradually fell during storage, which was not detectable at all after 20 days. Particularly, 1-octen-3-ol was undetectable in samples treated at 600 MPa on the 10 th day, revealing that extremely high pressure caused serious loss in 1-octen-3-ol. Figure 6: Effect of HHP treatment on volatile groups in kiwifruit pulp beverage on day 0. Control, kiwifruit pulp beverage treated without HT or HHP. HT, heat treatment (85 \({}^{\circ}\)C for 10 min). HHP, high hydrostatic pressure (400–600 MPa for 5–15 min). Results were expressed as means \(\pm\) SD, \(n=3\). The total content of aldehydes decreased while the content of the other four volatile groups (alcohols, ketones, esters and acids) increased along the time of storage (Figure 8). [PERSON] and [PERSON] [56] also observed reduction of many aldehyde compounds content after 60-day storage in HHP-treated guava juice. In first 20 days, no difference was found in total aldehydes content of different treated samples. Interestingly, HHP at 500 MPa/15 min and 600 MPa/15 min maintained higher total aldehydes content on the 40 th day, indicating that these two treatments were more favorable for the retention of aldehydes compared with HT and the rest of HHP treatments. Figures 8B and 8C clearly showed that the total content of ketones and alcohols in pulp beverage processed at 500 MPa for 10 min increased  
Figure 7: Changes of main volatiles in heat-treated and HHP-treated kiwifruit pulp beverage during storage at 4 °C for 40 days. (**A**) Hexanal content; (**B**) _E_-2-hexanal content; (**C**) 1-octen-3-one content; (**D**) 1-penten-3-one; (**E**) 1-hexanol content; (**F**) 1-octen-3-ol content.