Protection of color and chemical degradation of anthocyanin from purple corn (Zea mays L.) by zinc ions and alginate through chemical interaction in a beverage model

Anthocyanin-rich purple corn pericarp water extract (PCW) has the potential to be used as a natural pigment in beverages. However, it has a limited shelf-life in aqueous solutions. The aim was to evaluate the effect of zinc ion (Zn2+) and alginate on color and chemical stability of anthocyanins from colored corn (PCW) in a beverage model for 12 weeks. PCW was incorporated to Kool-Aid (R) Invisible (TM) along with ZnCl2 and/or alginate. Individual ANC were quantified through HPLC, and color stability was evaluated through the CIE-L*a*b* color system. Complexation between PCW and Zn/alginate was evaluated with fluorescence spectroscopy. The combination of Zn and alginate was the most effective treatment improving the half-life of total ANC concentration (10.4 weeks), cyanidin-3-O-glucoside (7.5 weeks) and chroma (18.4 weeks), compared to only PCW (6.6, 4.5 and 12.7 weeks, respectively). Zn and alginate had bimolecular quenching constants (Zn k(q): 3.4 x 10(11) M-1S-1 and AA k(q): 1.0 x 10(12) M-1S-1) suggesting that fluorescence quenching was binding rather than collisional. Results suggested that Zn/alginate interacted with ANC from purple corn slowing its chemical degradation.