Degradation of folate limited in vegetables.

Folates of the vitamin B family play an important role in the metabolism of amino and nucleic acids. Not consuming enough folate can potentially lead to several disorders, cancers and diseases. Research has shown that non-thermal high-pressure processing and preservation techniques applied to plant-based foods can have an influence on folate stability.

Belgian scientists studied the mechanisms and kinetics of vitamin stability, specifically folate stability, during high-pressure processing. They believed that vitamin stability might be affected during high-pressure processing because undesired chemical reactions could be enhanced. Consequently, it might be necessary to take into account nutrient stability when high pressures are combined with elevated temperatures, as in high-pressure sterilization. However, a validation study shows that folate degradation in vegetables treated with high pressure is limited by the existence of endogenous ascorbic acid.

The investigators extended their research to include intact vegetables so they could validate their results. To generate basic insight into the mechanisms and kinetics involved, they diluted 5-methyltetrahydrofolate (5MTHF, m/z 460) in various buffer solutions. The researchers carried out either temperature or high-pressure treatments in a multivessel pressure apparatus at 100 MPa to 700 MPa and at 10 C to 60 C for different periods of time.

Folate concentrations were quantified using reversed-phase high-performance liquid chromatography, and degradation products were identified using the same technique. The scientists estimated water-soluble antioxidant capacity as they quantified the Trolox equivalent antioxidant capacity (TEAC) and vitamin C content using reversed-phase high-performance liquid chromatography.

The researchers found that folate degradation was primarily caused by oxidation--the formation of 6-hydroxy-5-methyl-5,6-dihydrofolate. The scientists were able to depict the mechanism involved in oxidation. In the pressure-temperature-time combinations studied, the oxidation products could be completely reduced by antioxidants.

Kinetic data indicated that the oxidation rate accelerated as pressure and temperature increased, and decelerated when antioxidants were added. Folate oxidation at 0.1 MPa occurred at lower temperatures when a pressure of more than 50 MPa was applied.

Further information. Ann Van Loey, Centre for Food and Microbial Technology, Katholieke Universiteit Leuven, Room 01.64, Center Levensmidd. and Microbial Technology, Kasteelpark Arenberg 23, Bus 2457, 3001 Heverlee, Belgium; phone: +32 16 321567; fax: +32 16 321960; email: ann.vanloey@biw.kuleuven.be.