Antioxidant activity comparison between [6S]-5-methyltetrahydrofolic acid calcium salt and the related racemate form

Folates, such as [6S]-5-methyltetrahydrofolic acid, have been introduced in the market both in vitamin pills and in fortified foods. Their antioxidant activity has been evaluated, but stereoisomer influence on activity has not been proven. In this study, a comparison between [6S]-5-methyltetrahydrofolic acid (5-MTHF) and its racemate [6R,S] form was made by TEAC assay at different pHs, FRAP assay, and ORAC assay. The results showed that the [6S] form had higher antioxidant activity than its racemate form in the TEAC assay at all pHs, with similar values in the FRAP and ORAC assays. Results suggest that stereoisomeric difference could influence the antioxidant activity of 5-MTHF and hence should be taken into account when folates are added to foodstuffs to improve their nutritional value.