Electrochemical Determination of Ascorbigen in Sauerkrauts

Abstract

Ascorbigen (ABG), 2-C-(indol-3-yl)methyl-α-Lxylo-hex-3-ulofuranosono-1,4-lactone, was synthesised and its structure and purity was confirmed by means of 1 H NMR and 13 C NMR spectra and HPLC-PDA, respectively. The electrochemical behaviour of ABG was studied by cyclic voltammetry (CV) method for pH within the range of 3.0-7.0 and further characterisation was performed by differential pulse voltammetry (DPV) at pH 5.0. Voltammetric studies of ABG at glassy carbon electrode showed one irreversible oxidation peak (centred at E p =0.950 V for pH 5.0). The anodic peak current potential related to the irreversible oxidation of ABG was shifted towards more positive potentials with decreasing pH values. The linear response between concentration of ABG within the range of 0.08-0.75 mM and recorded current was observed. The DPV method was shown to be more sensitive when compared to the CV method. ABG showed a significant reducing activity provided by CV, whilst the antioxidant activity of ABG against O 2 −• was negligible. Electrochemical behaviour of ABG standard was applied successfully for the quantification of natural ABG in sauerkrauts by DPV and HPLC-CoulArray methods. Based on the developed analytical methods, ABG content increased during natural fermentation of cabbage at 0.5% and 1.5% NaCl levels, and results were comparable with those found in the literature.

Ascorbigen A—NMR identification

“…The 13 C chemical shifts measured in DMSO and water (Table , Figure ) are in reasonable agreement with those measured previously in CD 3 OD solutions . The appearance of 1 H NMR spectra of ascorbigen A, however, is distinctly different in different solvents (Table , Figure ).…”

“…In contrast to all published NMR spectra of ascorbigen A, spectra recorded in dry DMSO reveal the presence of one NH ( δ = 10.89, a poorly resolved doublet with an apparent splitting of 2.4 Hz) and three OH groups around δ = 7.0 (s), 5.6 (s), and 5.4 (a broad singlet in concentrated solution and a doublet with apparent J = 4.2 Hz in diluted solution) with their chemical shifts being concentration, impurity, and temperature dependent. (An NMR study of indol‐3‐ylmethyl oligomers, which included ascorbigen, in DMSO did not report shielding of its labile protons.)…”

“…A literature survey revealed that the structure of ascorbigen A has not been determined either by NMR or by X‐ray diffraction. The NMR signals were self‐consistently assigned to the respective atoms in the widely accepted molecular formula previously suggested in 1966. Moreover, the solvents used in these NMR studies (methanol, chloroform + methanol, pyridine, and D 2 O) precluded observation of OH and NH proton signals; their positions on the carbon skeleton have thus remained ambiguous.…”

Influence of fermentation on glucosinolates and glucobrassicin degradation products in sauerkraut

“…The synthesis was carried out according to Zielinska, Frias, Penas, Valeverde, & Zielinski (2012 Cabbage (50 g) was placed into 200 mL of boiling water and stirred for 5 min. The mixture was cooled to room temperature and homogenised with Ultra-Turrax.…”