## 3 Results and Discussion
### Volatiles Analysis
#### Changes of Volatiles in Kiwifruit Pulp Beverage after HHP
HHP and heat treatments resulted in significant (_p_ < 0.05) enhancement in the levels of hexanal and _(E)_-2-hexanal, which may be related to autoxidation of lipid in fruit and enzymatic oxidation reactions [47]. Linoleic acid and linolenic acid are converted into hydroperoxides, the 13-hydroperoxide produced is easily converted to C6 aldehyde through cleavage by a hydroperoxide lyase [48]. Moreover, kiwifruit pulp beverage processed at 400 MPa for 5 min showed the highest hexanal content, which was significantly different from heat-treated samples. [PERSON] et al. [49] also observed an increase in hexanal content of tomato juice after HHP treatment (500 MPa/3 min). In comparison, the higher increase of _(E)_-2-hexanal content was found in pulp beverage treated at 400 MPa for 10 min. The increase in these volatiles may contribute to maintaining freshness of kiwifruit pulp beverage because hexanal imparts grassy notes to kiwifruit and _(E)_-2-hexanal is responsible for green and fruity aroma. Significant (_p_ < 0.05) decrease of 1-hexanol content and increase of 1-octen-3-ol content as well as 1-octen-3-one content were observed after heat and HHP treatments. Additionally, the highest levels of these three compounds were detected in HHP treatment at 400 MPa for 10 min. Previous study also observed a significant reduction in 1-hexanol content as well as an increase in the level of 1-octen-3-ol in HHP-treated (400 MPa for 1 and 150 s) red plum puree with respect to the untreated pure [50]. HHP treatment activated the activity of some glycosides, so that the glycoside-bound alcohol in kiwifruit pulp beverage was released [51]. Different treatments showed different impacts on 1-penten-3-one. With the exception of HHP treatments (400 MPa for 15 min and 500 MPa for 5-10 min), which had no significant effect on 1-penten-3-one content, the other HHP treatments resulted in significant increase in 1-penten-3-one content. Furthermore, higher 1-penten-3-one content was found in samples processed at 400 MPa for 5 min. Effect of HHP treatment on volatile groups in kiwifruit pulp beverage was shown in Figure 6. We calculated the sum of peak areas to get the total amount of volatile compounds for a particular group (e.g., alcohols, aldehydes, ketone, esters, and acids). Through the sum we can evaluate the effect of different treatments on volatile compounds for a particular group. Analysis of volatiles showed that aldehydes and alcohols were the most represented classes of compounds in kiwifruit pulp beverage. Aldehydes play an important role in the characteristic aroma of kiwifruit pulp beverage [50]. HHP and heat treatments improved the flavor of pulp beverage since they significantly (_p_ < 0.05) enhanced the total aldehydes content. Besides, the highest increase of aldehydes content was observed in samples treated at 500 MPa for 10 min. Similarly, the total content of aldehydes in red plum puree was also slightly increased after HHP treatment [50]. HHP treatments (400 MPa for 5 min/10 min) significantly increased the total ketones content while decrease of ketones concentration was detected in HT and the rest of HHP treatments. By contrast, the total content of alcohols and esters in all treated samples fell significantly, which may be attributed to oxidation of alcohols after treatments, thereby producing aldehydes [52]. Interestingly, this also would be part of the reason for the increase in the aldehydes content of treated samples. These results were similar to previous study about red plum puree and model systems containing fruit esters in buffer solution, in which the total arbitrary area units of alcohols and esters decreased respectively after HHP [45; 50]. Among all treatments, the significantly higher alcohols concentration in pulp beverage treated at 400 MPa for 10 min suggested that this treatment could be positive to preserve alcohols in pulp beverage. As for acid compounds, the total content of acids in samples increased by HHP treatment at 400 MPa for 15 min.