pH-Dependent radical scavenging activity of folates.

Folic acid (FA) is used, in many countries, in nutritional supplements or for the fortification of cereals and their products. It is also used in vitamin pills. Recently, it was reported that folates may act as antioxidants; therefore, in the present study, the effect of pH of the surrounding medium on the radical-scavenging activity of FA and its reduced forms [dihydrofolic acid (DHF), tetrahydrofolic acid (THF), 5-methyltetrahydrofolic acid (5-MTHF), and 5-formyltetrahydrofolic acid (5-FTHF)] was investigated. It was found that radical-scavenging activities of folates, measured in the trolox equivalent antioxidant capacity (TEAC) assay, are strongly pH-dependent. FA is a better radical scavenger at acid and basic pH than at neutral pH. Reduced forms of FA are better radical scavengers at acidic pH values than at neutral and basic pH values, with exception of 5-FTHF for which, at a pH higher than 5.0, an increase of the radical-scavenging activity with an increasing pH of the medium is observed. The results of the present study indicate that possible health effects of folates associated with their radical-scavenging activity will vary depending upon the pH of body fluid or tissue considered.