## 3. Results and Discussion
### Antioxidant Activity of FPs  
Polysaccharides can be used as natural free radical scavengers with potential antioxidant activity [20]. The scavenging capacity of DPPH free radicals is widely used to determine the antioxidant capacity of polysaccharides [42]. Figure 8A shows the scavenging ability of the four polysaccharides and Vc on DPPH radicals. All FPs had DPPH radical scavenging ability and the scavenging ability was positively related to their concentrations. The results showed that the DPPH radical scavenging rates of FPF, FPV, FPH and FPFI were 70.12%, 63.47%, 57.41% and 60.45%, respectively. In addition, the IC\({}_{50}\) values of DPPH radical scavenging (Figure 8B) by FPF, FPV, FPH and FPFI were 0.403 mg/mL, 0.592 mg/mL, 0.934 mg/mL and 0.709 mg/mL, respectively. It is proved that FPF can achieve better DPPH free radical scavenging effect with a relatively low dose. All polysaccharides were less effective than Vc in scavenging free radicals, and the order of their scavenging ability was FPF \(>\) FPV \(>\) FPFI \(>\) FPH. Polysaccharides and ABTS radicals are scavenged by hydrogen-donating scavenging and combine into stable ABTS molecules to achieve scavenging of ABTS radicals [43]. As shown in Figure 8C, FPF, FPV, FPH and FPFI all had scavenging ability for ABTS radicals and the scavenging ability increased with increasing polysaccharide concentration. Figure 8: Antioxidant activities in vitro of FPF, FPFI, FPH and FPV: (**A**) scavenging ability on DPPH, (**B**) IC\({}_{50}\) of DPPH scavenging ability, (**C**) scavenging ability on ABTS, (**D**) IC\({}_{50}\) of ABTS scavenging ability, (**E**) reducing ability of ferric ion. Note: Different superscript lowercase letters (a–d) are significantly different (\(p<0.05\)). The clearance of FPH and FPV was significantly lower than that of FPF and FPFI when the concentration range was 0.5-1.5 mg/mL. FPF, FPV, FPH and FPFI all reached their maximum clearance after 1.6 mg/mL, which was 67.81%, 53.48%, 47.96% and 63.71%, respectively. The IC\({}_{50}\) for clearance of ABTS (Figure 8D) by FPF, FPV, FPH and FPIR were 0.563, 1.242, 2.013 and 0.678 mg/mL, respectively. It was proven that FPF and FPFI were effective in scavenging ABTS radicals. FRAP reduction capacity is the reduction in trivalent iron ions (Fe\({}^{3+}\)) to ferrous ions (Fe\({}^{2+}\)) by polysaccharides by providing electrons [44]. The stronger reducing power of FRAP indicates the stronger antioxidant activity of polysaccharides. Figure 8E shows the FRAP reduction capacity of the four polysaccharides. All polysaccharides showed reduction capacity and lower reduction power than Vc. Among the four FPs samples, FPFI had the strongest reducing power followed by FPF and FPV, and FPH had the worst reducing power. It has been reported that the antibody oxidation activity of natural polysaccharides is closely related to its structural composition [35]. Pearson correlation coefficient was used to analyze the correlations among molecular weight, monosaccharide composition,uronic acid, apparent viscosity and antioxidant capacity of FPs, and the results were normalized by column, as shown in Figure 5 The DPPH radical scavenging activity of FPs was significantly positively correlated with the content of uronic acid (**), and significantly negatively correlated with Glc (*) and Man (*). The ABTS radical scavenging activity of FPs was positively correlated with uronic acid content (***) and GalA (**), and negatively correlated with molecular weight (**), apparent viscosity (**) and Gal (**). The iron reduction capacity of FPs was positively correlated with uronic acid content (**) and Rha (*), and negatively correlated with molecular weight (***), apparent viscosity (***) and Ara (*). The results were consistent with the previously reported correlation between antioxidant activity of polysaccharides and low molecular weight and high content of uronic acid [40]. [PERSON] et al.