In their study dealing with iron effects on DNA strand breaks, Flemmig and Arnhold show that plasmid strand breaks is not mediated by hydroxyl radical produced from hydrogen peroxide in Fenton reaction but essentially by iron [18]. To determine working conditions so that DNA degradation is induced by •OH, in our study the reaction mixture proposed by Kitts et al. was used [17]. In order to observe pUC18 strand breaks only induced by •OH production, an assay with no iron effect was developed (Figure 1). To that end, the mixture were incubated 20 min at 37 °C and various EDTA and FeSO4 concentrations were tested keeping a molar ratio of 0.53 between EDTA and FeSO4 as specified by Repine et al. [22]. In this assay, we looked for a condition wherein the supercoiled form (form I) was totally degraded by H2O2 addition and then protected by adding an antioxidant compound, the trolox. In this approach, final concentrations of 0.33 mM of FeSO4 and 0.62 mM of EDTA were identified as optimal conditions to evaluate aqueous extracts •OH nicking protection capacity (lanes 11–13) (Figure 1). However, using this conditions we can notice that using FeSO4 and EDTA alone induce the formation of plasmid open circular form (form II), but did not induce plasmid linearization (form III) (lane 11) (Figure 1). These results led us to quantify the percentage of pUC18 form I (native form) and form III (nicked linear DNA) to evaluate both antioxidant or prooxidant capacity of extracts. Due to the slight over or under formation of the form II we chose to do not quantify its formation. The results obtained with pUC18 plasmid in this study confirmed the iron effect on strand breaks of the pBR322 plasmid already shown in Flemmig and Arnhold’s work [18]. Actually, if the iron concentration is not adapted, both plasmids (pUC18 and pBR322) are mostly cleaved by iron instead of •OH induced by the Fenton reaction.