## 3 Results and Discussion
### Effect of HHP on Vitamin C Content in Kiwifruit Pulp Beverage  
As an essential nutrient component in kiwifruit, vitamin C is not stable and always decomposed and oxidized when exposed to light and oxygen. Consequently, VC content is considered as an important index of oxidative deterioration in fruit juices [32]. As can be seen in Figure 1, HHP and heat treatments caused a pronounced reduction in VC content (\(p<0.05\)). Interestingly, samples processed at 400 MPa for 15 min showed the highest VC content with 35.8% higher VC retention compared toHT. Similarly, [PERSON] et al. (2018) found that HHP-treated green bell peppers showed a higher vitamin C retention than the samples treated by thermal blanking at 80 \({}^{\circ}\)C and 98 \({}^{\circ}\)C.  
Kiswifruit pulp beverage showed a gradual decrease in VC content during storage, proving that vitamin C degraded with time (Figure 2). This is in line with the result of [PERSON] et al. (2018) who observed a significant reduction in VC content when the storage time progressed. Moreover, the degradation rate of vitamin C in the early stage of storage was greater than that in the later stage of storage, which may be due to a decrease in oxygen concentration during storage, thus the degradation of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Treatments**} & \multicolumn{4}{c}{**Storage Time (Day)**} \\ \cline{3-5}  & **0** & **10** & **20** & **40** \\ \hline \multirow{3}{*}{HT} & Control & 3.03 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.02 \({}^{\mathrm{a}}\) \\  & & 3.02 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.00 \({}^{\mathrm{a}}\) \\  & 5 min & 3.01 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.29 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) \\
400 MPa & 10 min & 3.02 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.27 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.01 \({}^{\mathrm{a}}\) \\  & 15 min & 3.00 \(\pm\) 0.03 \({}^{\mathrm{b}}\) & 3.27 \(\pm\) 0.02 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.27 \(\pm\) 0.02 \({}^{\mathrm{a}}\) \\  & 5 min & 2.99 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.29 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.02 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.03 \({}^{\mathrm{a}}\) \\
500 MPa & 10 min & 3.01 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.27 \(\pm\) 0.01 \({}^{\mathrm{a}}\) \\  & 15 min & 3.02 \(\pm\) 0.01 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.00 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.03 \({}^{\mathrm{a}}\) \\  & 5 min & 2.98 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.02 \({}^{\mathrm{a}}\) & 3.27 \(\pm\) 0.02 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) \\
600 MPa & 10 min & 3.00 \(\pm\) 0.01 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.02 \({}^{\mathrm{a}}\) & 3.28 \(\pm\) 0.02 \({}^{\mathrm{a}}\) \\  & 15 min & 3.03 \(\pm\) 0.02 \({}^{\mathrm{b}}\) & 3.28 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.01 \({}^{\mathrm{a}}\) & 3.29 \(\pm\) 0.02 \({}^{\mathrm{a}}\) \\ \hline \hline \end{tabular} 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, \(n=3\). Different letters indicate the data are different significantly (\(p<0.05\)).  
\end{table} 
Table 1: Changes in pH of heat-treated and high hydrostatic pressure (HHP)-treated kiwifruit pulp beverage during storage at 4 \({}^{\circ}\)C for 40 days. Figure 1: Vitamin C content of HHP-treated and heat-treated kiwifruit pulp beverage after 0 day. Control (kiwifruit pulp beverage treated without heat treatment (HT) or HHP).