Folates as antioxidants

Folic acid (FA) and its physiological reduced forms: 7,8-dihydrofolate (DHF), 5,6,7,8-tetrahydrofolate (THF) and 5-methyltetrahydrofolate (5-MTHF) were studied for their antioxidant activities using trolox equivalent antioxidant capacity (TEAC) assay with ABTS+ radical cation, 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and ferric reducing antioxidant power (FRAP) assay. Moreover, literature data on peroxynitrite (PON) scavenging activity and inhibition of lipid peroxidation (LPO) by folates are included. It was found that reduced forms of FA have approximately 3.5–7.5 fold, 12–16 fold and 44–71 fold higher activities than those of FA in the DPPH, TEAC and FRAP assays, respectively. Their antioxidant activities are comparable to those of vitamin C and E, which are commonly accepted as the effective water and lipid soluble antioxidants. Although natural folates cannot be really considered as food antioxidants, they may act as effective antioxidants in vivo. Their activities may become important in view of nutritional supplementation and fortification of food with FA.