## 3 Results
### The Antioxidant Properties of RCE, RA, and CA In Vitro and in Aoil  
RCE, RA, and CA showed an effective efficiency in free radical scavenging capacity, where the free radical scavenging capacity increased with raising concentrations of a tested compound (Figure S2). The antioxidant capacity of RCE, RA, and CA was compared with the synthetic antioxidants the TBHQ, BHA, BHT, and the natural antioxidant \(\alpha\)-T using DPPH, ABTS, FRAP, and PTIO analyses. The results of DPPH and PTIO testing showed that RCE, RA, and CA had higher antioxidant activity than BHA and BHT, but a slightly lower effect compared to TBHQ. The results of DPPH and ABTS showed that RCE, RA, and CA had similar antioxidant activities to \(\alpha\)-T (Figure 3A,B). FRAP analyses showed that RCE and RA had higher antioxidant activities than CA, TBHQ, BHA, BHT, and \(\alpha\)-T (Figure 3C). The results of the antioxidant potency composite showed that RCE and CA  
Figure 1: (**A**), Geographic distribution map of _Acer truncatum_ in the world and China. (**B**), _Acer truncatum_ (**B1**), leaves (**B2**), fruit (**B3**), seed (**B4**), and oil (**B5**) of _Acer truncatum_. (**C**), Percentage of different types of fatty acids in the Aoil. (**D**), Fatty acid composition of the Aoil.  
had a higher antioxidant activity than BHA, BHT, and \(\alpha\)-T and a slightly lower antioxidant activity than TBHQ. However, RA had higher antioxidant activity than TBHQ, BHA, BHT, and \(\alpha\)-T (Figure 3E). Overall, DPPH, ABTS, FRAP, and PTIO analyses showed that RA has a higher antioxidant activity in vitro.  
The antioxidant property of RCE, RA, and CA in Aoil were preliminarily assessed by determination of the oxidation products. The greater the MDA content, the more serious the oxidation of the oil. The MDA values demonstrated that total MDA concentration in the Aoil consequently rises due to accelerated oxidation during the period from 0 to 30 d (Figure 3F). After an oxidation period of 30 d, the oils enriched with RCE and CA had lower MDA content than those enriched with BHA, BHT, and \(\alpha\)-T, but had a slightly higher MDA content than those enriched with TBHQ oil. Based on the results on MDA inhibition rate, the CA had the strongest protective effect on Aoil among RCE, RA, and CA (Figure 3G). The FFA assay results were similar to those of the MDA assay. The concentration of the total FFA in Aoil increased with the accelerated oxidation time from 0 to 30 d (Figure 3H). After oxidation for 30 d, the oils enriched with RCE and CA had a lower FFA content than oils enriched with BHA, BHT, and \(\alpha\)-T, as well as a slightly higher FFA content than oil enriched with TBHQ. The results of the inhibition rate of FFA showed that CA had the strongest protective effect on Aoil among RCE, RA, and CA (Figure 3I). Both MDA and FFA results indicated that RCE, RA, and CA can significantly inhibit the oxidation of Aoil. However, CA has better oxidative stability to Aoil among RCE, RA, and CA.  
Figure 2: Analysis of the RCE (**A**), RA (**B**), and CA (**C**) powder. (**D**), RCE composition analysis. (**E**), Purple: HPLC data for RA standard; green: HPLC data for RA obtained by the preparative liquid chromatograph from the RCE; red square: HPLC data for impurities in RA. (**F**), Purple: HPLC data for CA standard; green: HPLC data for CA obtained by the preparative liquid chromatograph from the RCE.