Steering the color of the retro-carotenoid rhodoxanthin by (E/Z)-isomeric ratios, controlled aggregation, and formulation technology

Food and beverage processors are urgently calling for new sources of vibrant red to purple colorants to replace the increasingly rejected artificial dyes and the insect-derived carmine. Finding alternative solutions to fill this unmet market need based on equipotent natural or nature-identical pigments, such as carotenoids that impart yellow to red colors to plants, is a continuing challenge. The color of colloidally stabilized formulations of carotenoids can be modulated by manipulating (E/Z)-isomeric ratios, deposition states, and particle sizes. However, to date, none of the commercially available carotenoid formulations conveys bright red to purple color shades. The yet scarcely studied retro-carotenoids commonly feature enlarged chromophores and exceptional light absorption properties that offer new opportunities to yield such color hues. This doctoral thesis presents analytical investigations of retro-carotenoids and practically feasible formulation approaches to exploit rhodoxanthin as highly potent pigment for conveying intense red and purple colors to foods and beverages. Carotenoid profiles of Taxus arils were elucidated and identified as an abundant natural source of retro-carotenoids. A detailed description of kinetic and thermodynamic parameters of rhodoxanthin’s complex (E/Z)-isomerization reactions enabled defining technological measures to modulate the color of rhodoxanthin formulations by tailoring (E/Z)-ratios and controlling aggregations. This body of research on rhodoxanthin paves the way for the replacement of red- and purple-colored artificial dyes and carmine in the food industry, addressing their increasing rejection by consumers around the globe.