## 3 Results and Discussion
### Effects of Domestic Cooking on Changes in the TPC, TFC and Antioxidant Activities of Faba Leaves
The variation in the DPPH/ABTS radical scavenging abilities of the freeze-dried and cooked faba leaves are shown in Figure 3C,D, respectively. Briefly, similar patterns in both measurements of antioxidant activity of the faba leaves were observed: they were increased by the microwaving treatment, not significantly changed by the roasting treatment, maintained by the boiling treatment, and the steaming treatment significantly increased the DPPH radical scavenging ability but not the ABTS radical scavenging ability. One explanation could be that even though the \(\iota\)-dopa content was increased by steaming, there was no significant change in the TPC (Figures 2C and 3A). High levels of \(\iota\)-dopa, vitamin C, TP, and TF have been reported to be responsible for strong antioxidant activity in dry heated and wet heated faba leaves [3]; however, in the present study, the correlation analysis suggested that the radical scavenging activities of fresh and cooked faba leaves were mainly caused by the \(\iota\)-dopa content (0.863 with DPPH radical scavenging activity; 0.856 with ABTS radical scavenging activity) and TPC (0.854 with DPPH radical scavenging activity; 0.979 with ABTS radical scavenging activity), not by the individual flavonoid and TFC content (Table S1). \(\iota\)-dopa has been reported to be an effective antioxidant in several in vitro assays such as radical scavenging, reductive ability and anti-lipid peroxide [29]. Even flavonol glycosides have been reported to also contribute strong antioxidant activities in numerous plants, and the activities are significantly varied depending on flavonol types and contents [30]. \(\iota\)-dopa is a predominant compound that exists in faba leaves among the polyphenols detected in this study (Figure 2 and Table 2). Our previous study has suggested that \(\iota\)-dopa is more powerful than vitamin C in terms of radical scavenging abilities [3]. Moreover, a high correlation was observed between the DPPH radical scavenging ability and \(\iota\)-dopa content, compared with that found between the ABTS radical scavenging ability and TPC. These findings can be supported by a previous study where the same concentration of an \(\iota\)-dopa standard compound (0 to 20 mM) exhibited a stronger DPPH  
Figure 3: Changes in TPC (**A**), TFC (**B**), DPPH radical scavenging ability (**C**), and ABTS radical scavenging ability (**D**) of faba leaves after treatment by four domestic cooking methods (FD: freeze-dried (Control); MW: microwaving; RT: roasting; SM: steaming; BL: boiling). Values are averages with standard errors from triplicate experiments. Different letters on the graph bars indicate significant differences at \(p<0.05\) ([PERSON]’s HSD test). radical scavenging ability than the ABTS radical scavenging ability [3]. Here, it is important to point out the different mechanisms for evaluating antioxidant action between DPPH and ABTS assays [31; 32]. In a DPPH assay, DPPH is a specialized lipophilic radical, which can be neutralized into the reduced forms of either DPPH-H (by receiving a hydrogen atom) or DPPH (by accepting an electron); however, the ABTS assay is suitable when evaluating antioxidant components which have a hydrophilic or lipophilic character. The assay is only based on a hydrogen atom transfer reaction. Additionally, the important parameter when evaluating the antioxidant action of a single electron transfer is ionization potential, whereas that of hydrogen atom abstraction is bond dissociation enthalpy.