Profiles of products generated during betacyanins reduction by 2-methylpyridine borane

Betanin and neobetanin (14,15-dehydrogenated betanin), natural betacyanin pigments were subjected to a gentle reduction by 2-methylpyridine borane. During each reduction reaction, the visible spectra were collected. The results were tentatively confirmed by LC-DAD-ESI-MS. In comparison to a previous study with sodium borohydride, various types of products were obtained. Depending on pH, one or two double bonds are reduced. Interestingly, a preliminary decarboxylation of the pigments is also noticed. Betacyanins are plant red-violet pigments applied as colorants in food and pharmaceutical industry which are proven to have an antioxidant activity. They are confirmed to be beneficial for human health as free radical scavengers. Therefore, betacyanins can prevent from many diseases which would be induced by an excessive accumulation of free radicals in the human body. There are more and more reports of their pro-health properties. However, the mechanism of betacyanins oxidation remains not completely elucidated. It is postulated that the rearrangement in the chromophoric system is a significant part of this mechanism. The products obtained as a result of reduction of betanin and neobetanin can be useful in oxidation investigations. Betacyanins with partially destroyed chromophoric system by reduction of the double bonds would by perfect models for further studies on their oxidation.