## Results
### The Assessment of Taste of Flat Peaches from Xinjiang
#### 3.2.2 Antioxidant Activity In Vitro in Flat Peaches from Xinjiang  
Antioxidant polyphenolic compounds provide hydrogen ions, electrons, and metal chelation, which are beneficial to human health [31; 69]. The ABTS\({}^{+}\) radical scavenging capacity and DPPH radical scavenging rate, CUPRAC, and FRAP reducing capacity were determined to characterize the antioxidant activity of phenolic compounds in flat peaches (Qingpan, QP; Ruipan 2, R2; Ruipan 4, R4; Wanpan, WP) from Xinjiang, shown in Table 2. The ABTS\({}^{+}\) radical scavenging capacity and DPPH radical scavenging rate of the flat peaches ranged from 165.40 to 324.38 umol TEs/100 g and 207.93 to 799.16 umol TEs/100 g, respectively. R4 had the highest ABTS\({}^{+}\) radical scavenging capacity and DPPH radical scavenging rate, but WP was the lowest. This may also be due to the high content of hydrogen donor molecules in flat peaches, which could reduce the production of free radicals, thus reflecting higher free radical scavenging activity. In addition, FRAP and CUPRAC reducing capacities are other important indicators reflecting the potential antioxidant activity in flat peaches. In the experiment, the CUPRAC reducing capacity of the flat peaches was between 44.69 and 1145.90 umol TEs/100 g, and the FRAP reducing capacity of the flat peaches ranged from 57.56 to 1252.00 umol TEs/100 g. More importantly, R4 exhibited superior antioxidant capacity; two to three times more than the other three flat peaches. Early research reported that antioxidant capacity assay in vitro could reveal the main functional characteristics of fruit tissues [70]. In the present study, it was revealed that R4 demonstrated a strong antioxidant capacity in vitro. The antioxidant effect of peaches has been demonstrated in previous experiments [67; 71]. Based on the results of this study, flat peaches have significant potential as an antioxidant ingredient in animal feed or human health food. 2.3 Correlation Analysis of Phenolic Compounds and Antioxidant Capacity of Flat Peaches from Xinjiang  
Antioxidant capacity is generally the basic ability of phenolic compounds to prevent or treat diseases [72]. To investigate the relationship between phenolic compounds and antioxidant activity in flat peaches, with polyphenol and flavonoid content as independent variables and antioxidant activity as the dependent variable, the following results were obtained by multi-dimensional data analysis using O2 PLS models combined with correlation coefficients. When the VIP value was more than 1, this proved that the phenolic compounds were more correlated with the antioxidant capacity. Proanthocyanidin B1 (D), chlorogenic acid (H), catechchin (F), neochlorogenic acid (E), epicatechin (I), rutin (J), and total phenols (B) correlated more strongly with antioxidant capacity (Supplementary Figure S3). In Figure 4, the correlation coefficient matrix reveals that epicatechin, rutin, catechchin, proanthocyanidin B1, chlorogenic acid, neochlorogenic acid, and total phenols were positively correlated \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Variety**} & \multicolumn{2}{c}{**Radical Scavenging Capacity**} & \multicolumn{2}{c}{**Reducing Capacity**} \\ \cline{2-5}  & **ABTS\({}^{+}\)** & **DPPH** & **CUPRAC** & **FRAP** \\ \hline QP & 324.38 \(\pm\) 14.31 c & 464.54 \(\pm\) 12.87 b & 278.50 \(\pm\) 13.91 b & 297.56 \(\pm\) 3.85 b \\ R2 & 404.41 \(\pm\) 24.33 b & 398.04 \(\pm\) 17.27 c & 274.93 \(\pm\) 8.78 b & 279.78 \(\pm\) 8.39 b \\ R4 & 717.61 \(\pm\) 3.29 a & 799.16 \(\pm\) 5.57 a & 1145.90 \(\pm\) 26.32 a & 1252.00 \(\pm\) 67.66 a \\ WP & 165.40 \(\pm\) 13.71 d & 207.93 \(\pm\) 12.81 b & 44.69 \(\pm\) 3.52 c & 57.56 \(\pm\) 5.09 c \\ \hline \hline \end{tabular} Each value was the mean \(\pm\) standard deviation. Significant variations with a level of \(p\leq\) 0.05 (Duncan’s test) are shown by different letters for each sample. \({}^{*}\) denoted as cation.  
\end{table} 
Table 2: Antioxidant ability in vitro of flat peaches from Xinjiang (μmolol TEs/100 g FW).