| Molecules of anthocyanins and quinones possess distinctive electrophilic character, which is demonstrated by their facile reactions with nucleophiles such as sulfite, thiols, amines and water. In food systems, one of their likely targets would be nucleophilic centers in the side chains of amino acids. Our experiments revealed that on a short-term exposure (1 -- 72 h) to free amino acids in solutions with pH < 7 glycosides of cyanidin and quinones of phenolic acids did not yield nucleophilic addition products with most of the amino acids. A notable exception was cysteine, which reacted with oxidized phenolic acids and caused anthocyanin bleaching at elevated temperature. Thermodynamic aspects of the nucleophilic addition reactions were investigated with the aid of computational chemistry.;We have also found that enzymatic browning in apricot puree does not lead to trans-cis beta-carotene isomerization, contrary to some previous reports. Increased availability of beta-carotene for extraction was recorded for browned apple- and pear-apricot purees in comparison with the non-browned purees. |
