Redox properties of catechins and enriched green tea extracts effectively preserve L-5-methyltetrahydrofolate: assessment using cyclic voltammetry analysis.

A cyclic voltammetry (CV) study was performed in pH 5.5 Britton-Robinson buffer at room temperature to study the stability of 1mM l-5-methyltetrahydrofolate (l-5-MTHF) in combination with epigallocatechin-gallate-enriched extract (EGCGe) and epigallocatechin-enriched extract (EGCe). The combination of l-5-MTHF with enriched catechin extracts provided enhanced stability of l-5-MTHF over a period of 12h under ambient air conditions at pH 5.5. CV experiments showed that increasing the concentrations of EGCGe or EGCe extracts from 80 to 400mg/L produced a decrease in the second oxidation peak of l-5-MTHF. Thus, we calculated that l-5-MTHF remained at nearly 90% when in the presence of enriched tea extracts, compared to 74% without the tea antioxidants. The catechins responsible for this preservation were EGCG and C, confirmed by LC-MS. Compared to covalent link only low interaction (hydrogen bonds) between the different catechins present in the tea extract would stabilise l-5-MTHF. Rather, it was hypothesised that EGCGe and EGCe were effective agents to preserve l-5-MTHF, through a mechanism that also involved the redox potential of catechins to maintain l-5-MTHF in its reduced form.

Thermal oxidation studies on reduced folate, L-5-methyltetrahydrofolic acid (L-5-MTHF) and strategies for stabilization using food matrices.

The thermal stability of L-5-methyltetrafolic acid (L-5-MTHF) was investigated in model/buffer systems and food systems. L-5-MTHF degradation followed first-order reaction kinetics with relatively greater (P < 0.01) stability at pH 4 compared to pH 6.8 in the buffer systems. This was confirmed using cyclic voltammetry. The stability (for example, k-values) of L-5-MTHF in an oxygen controlled environment improved (P < 0.001) proportionally when in the presence of increasing molar ratios of sodium ascorbate (NaAsc). The addition of NaAsc to L-5-MTHF after heat treatment was also effective at returning thermally oxidized L-5-MTHF back to its original form. A scheme was developed to explain the degradation and regeneration of L-5-MTHF. The importance of antioxidant protection of L-5-MTHF from thermal oxidation was extended using 2 distinct food systems; namely skim milk and soy milk, both with known antioxidant capacities. We conclude that the antioxidant activity of food components can enhance the stability of L-5-MTHF.

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

A cyclic voltammetry study of 1mM l-5-methyltetrahydrofolate (l-5-MTHF) was performed in pH 5.5 Britton-Robinson buffer at room temperature to study the stability of l-5-MTHF alone and in combination with ascorbic acid (AA). The degradation of l-5-MTHF and AA over a period of 12h both followed first order reaction kinetics. Using this technique, oxidation peaks of l-5-MTHF were identified at +0.17 and +1.18V, and another oxidation peak appeared after 4h under air at +0.89V. Cyclic voltammetry and HPLC quantification enable us to confirm that l-5-MTHF can be highly preserved by the addition of an equimolar concentration of AA. This treatment was equivalent to a purge of nitrogen used to remove oxygen and thus minimise oxidation of l-5-MTHF when present in aqueous solutions. HPLC confirmed the fact that a full regeneration of oxidised l-5-MTHF occurred with the addition of sodium ascorbate, thus denoting that the redox character of l-5-MTHF can be controlled by the presence of reducing agents. Cyclic voltammetry proved to be a sensitive and accurate method for characterising l-5-MTHF oxidation and potential preservation with ascorbic acid. To our knowledge, this is the first study that has demonstrated the number of oxidation sites on l-5-MTHF.

Optical and physical properties of cobalt oxide films electrogenerated in bicarbonate aqueous media.

For the first time, cobalt oxide films that are highly protective against localized corrosion and depicting a wide variety of bright and uniform colors due to light interference, have been successfully electrogenerated on polycrystalline cobalt disk electrodes under potentiostatic polarization in a mild aqueous bicarbonate medium. Open circuit potential measurements have shown the formation of a film with a bilayered structure, organized as a thin Co3O4 outer layer and a thick CoO inner layer. The existence of Co3O4 as a thin outer layer, previously postulated from galvanostatic reduction experiments, has been confirmed from XPS analysis. Raman spectroscopy, performed using a very low laser intensity, has shown that the films are mainly composed of CoO. The broadness of the Raman bands observed is associated to the amorphous character of the film, a result that has been confirmed by spectroscopic ellipsometry and X-ray diffraction analysis. Overall film thicknesses, well controlled by the anodization duration, were determined and correlated using mechanical (atomic force microscopy and profilometry) and spectroscopic (specular UV-vis-NIR reflectance and ellipsometry) techniques. Spectroscopic ellipsometry, using a simple amorphous dispersion model, has proved efficient for measuring thicknesses of films ranging from 31 to 290 nm with very low standard deviations. The real part of the complex refractive indices of these films, ranging from 1.8 to 2.2 (at lambda = 632.8 nm) depending on the anodization duration, is in good agreement with values reported in the literature for CoO. The film with the highest refractive index, and consequently the more densely packed structure, was obtained following a 30-minute anodization period.