Anthocyanin elicitation for bio-sustainable colourant production in carrot

There is increasing demand for natural food colourants that can substitute synthetic colours due to both legislative restrictions and consumer concerns. Black or purple carrots (Daucus carota ssp. sativus var. atrorubens) have strong bluish-purple colour due to the natural pigment anthocyanin, which is used as natural food colourant due to its high pH, light, and heat stability (labelled E163 in Europe). However, new production and storage strategies of black carrot are required in order to increase pigment yield and, therefore, to be competitive against synthetic colours. In the present study, black carrot ‘Deep Purple’ was used in field experiments conducted in the 2015 growing season in Denmark, to determine if foliar applications of ethephon, an ethylene realising compound, can improve carrot anthocyanin content and yield. Total monomeric anthocyanins were measured spectrophotometrically, and anthocyanin composition was analysed by LC-MS/Q-TOF approach. The results documented substantial increase in anthocyanin concentration upon ethephon treatment, whereas root size was not affected. Five major cyanidin-based anthocyanin forms were detected, being the acylated (i.e., more stable) anthocyanins clearly predominant. In addition, a correlation between enhanced anthocyanin contents and decreased root dry matter and soluble sugar contents was found. Taken together, these traits make elicited ‘Deep Purple’ carrots a suitable basis for obtaining natural colourants.