Formation, tentative mass spectrometric identification, and color stability of acetaldehyde-catalyzed condensation of red radish (Raphanus sativus) anthocyanins and (+) catechin

Abstract

Red radish anthocyanins are relatively stable due to the acylation of anthocyanins with organic and phenolic acid moieties. The objective of this study was to create and identify a novel ethyl-bridged acylated anthocyanin with a stable violet color from red radishes in the presence of acetaldehyde and catechin. After incubation at ambient temperature for one week at 21◦ C the reaction mixture with acetaldehyde and catechin turned from bright red to a vivid purple color. The newly formed compounds were tentatively identified with liquid chromatography-electrospray ionization-mass spectrometry. Color stability (CIE L*C*h) was monitored over six months at 21◦ C and anthocyanin stability was evaluated by HPLC. Next, radishes were fermented by Zymomonas mobilis, a high acetaldehyde producing bacteria. Natural sources of catechin were used to replace the catechin standard, but the same purple color did not appear with the addition of cocoa powder or fava beans. The ethyliden-bridged radish anthocyanins possess excellent color stability and could serve as a natural food colorant.