ABSTRACT
The influence of stabilizing activity of citric buffers on betacyanins, as well as their thermal dehydrogenation and decarboxylation in a beetroot betalain-rich extract (BRE), was studied at pH 3-8 and temperature 30, 50 and 85 °C with an additional effect of EDTA. In acetate/phosphate buffers, the highest stability is observed at pH 5 and it decreases toward pH 3 as well as pH 8, which is more remarkable at 85 °C. For the citrates, a contradictory effect was observed. Citric buffers tend to stabilize the substrate pigments and their intermediary products in acidic solutions, although increase their reactivity at pH 6-8. The highest impact of EDTA addition on pigment retention in acetate buffers is observed at 85 °C and pH 3-5 as well as 8, reflecting the preserving activity of EDTA at the most unfavorable conditions. At lower temperatures, pigment stability in more acidic conditions is still at higher levels even without addition of citrates or EDTA. The most striking effect on generation of betanin derivatives during heating is 2-decarboxylation which preferentially proceeds in the most acidic environment and this generation rate at 85 °C is much higher in the citrate buffers compared to acetates.
Subject(s)
Beta vulgaris , Betalains , Betacyanins , Edetic Acid , Citrates , Decarboxylation , Chromatography, High Pressure Liquid , Plant ExtractsABSTRACT
Betacyanins are a group of water-soluble red-violet compounds containing nitrogen in their structure. These are biosynthesized in red beetroot (Beta vulgaris L.), a widely consumed vegetable that contains significant amounts of nutritious and bioactive compounds which are also found in dietary supplements. This contribution presents results of betacyanin thermal oxidation (resulting in dehydrogenation) interrelated with decarboxylation in selected acetate/phosphate buffers at pH 3-8 and at 85 °C, which may be of particular significance for formulation and performance of foods. Most of the reaction products were detected at the highest concentrations in the acidic solutions (pH 3-4). The main dehydrogenation reaction pathways were monitored by LC-DAD-MS/MS and were associated with decarboxylation of the principal extract pigments, betanin/isobetanin and neobetanin, at carbon positions C-2 and C-17. Additional reactions are accompanied by the 2,15-decarboxylation processes at different dehydrogenation levels with 15-decarboxy-betanin and 2,15-bidecarboxy-betanin, structurally elucidated by NMR analysis, as the distinct indicators of this route type. For other novel pigments detected, 2,15-bidecarboxy-xanbetanin, 2,15-bidecarboxy-xanneobetanin and 2,15,17-tridecarboxy-neobetanin, additional high resolution mass spectrometric analyses were performed and confirmed their molecular formulas.