Application of ferric anthocyanin chelates as natural blue food colorants in polysaccharide and gelatin based gels

Ferric anthocyanin chelates based on elderberry (EB-E) and purple carrot (PC-E) extracts as well as red cabbage juice (RC-J) were applied to different gel matrices to confirm their potential as natural blue food colorants. Blue color evolution and stability during storage at 4 and 20 °C in the dark and at 25 °C under illumination was monitored at two colorant concentrations by determination of lightness (L*), red (a*) and blue (b*) hue values as derived from tristimulus reflectance measurements. Intense blue hues were observed for gels based on gelatin (G) and a blend of agar-agar with amidated pectin (AA/AP). Under each of the storage conditions color stabilities of the gels with PC-E were excellent, being superior to those with added EB-E and RC-J. While room temperature (20 °C) and especially VIS light significantly affected blue color stability in gels dyed with EB-E and RC-J, color of the gels prepared with PC-E was almost fully retained independent of temperature and light exposure. Generally, enhanced stabilities were observed at higher colorant dosages. Gelatin improved color stability significantly compared to AA/AP gels, except for the PC-E colorant, where the difference between both matrices was negligible. Blue color decay in gels, as monitored by increasing b* values, partially deviated from first-order kinetics depending on colorant and storage conditions. Hence, kinetic calculations by exclusive consideration of the b* values were unsuitable for describing and predicting blue color loss. The formation of dairy based gums by substitution of water with yoghurt, buttermilk and milk was only supported by the aid of a gelatin matrix, resulting in pink, violet and slightly blue hues, respectively. In summary, the successful application of ferric anthocyanin chelates to food matrices was demonstrated, confirming their potential as promising natural blue food colorants.

► Development of gel matrices suitable for coloring with blue anthocyanin chelates. ► Improved blue color evolution and stability in gelatin based gels. ► Outstanding blue hues with colorant based on red cabbage juice. ► High stability, independent of storage conditions and gel matrix, for purple carrot.