The use of cyclic voltammetry to study the oxidation of l-5-methyltetrahydrofolate and its preservation by ascorbic acid

► l-5-MTHF is a natural reduced form of folic acid and could be used as food fortificant. ► Equimolar addition of ascorbic acid preserves l-5-MTHF from oxidation. ► It was demonstrated by cyclic voltammetry that l-5-MTHF has two oxidation sites on its molecule. ► A third oxidation peak appeared after 4 h under air at +0.89 V. ► Full regeneration of oxidised l-5-MTHF occurred with addition of sodium ascorbate.