Stabilization of natural pigments from purple corn pericarp in a beverage model through complex formation with metal ions and polysaccharides

Presenting author: Regina Cortez

Co-authors: Diego Luna, E G. Demejia

Department of Food Science and Human Nutrition

Natural pigments such as anthocyanins are an alternative to synthetic food colorants. The aim was to find the conditions to improve stability of color corn anthocyanins in a beverage matrix using metal ions and a polysaccharide. Beverages were prepared using purple corn pericarp water extract (PCW, 0.4 mg/mL), FeCl3 or ZnCl2 at either 0.2 or 0.4 mM, and sodium alginate (0.4%), by themselves and in combination, in a Kool-aid invisible matrix. Beverages were exposed to 3 temperatures (70, 80 and 90 °C) and tested at 0, 2, 4, and 6 h for color parameters l*a*b*, hue angle, and chroma, and concentration of total anthocyanins. The FeCl3 ion increased the rate of degradation of anthocyanins in solution (18.5 – 60.5%, p < 0.05) compared to the PCW control, with a maximum decrease of chroma (13.4%) after 6 h of incubation at 70 °C. ZnCl2 combined with alginate was effective at 70 °C. After 6 h of incubation at 70 °C, the beverage with ZnCl2 and alginate had an increase in total anthocyanins (33.4%, p< 0.05) compared to PCW. A possibly explanation was that the temperature increase caused disaggregation of the anthocyanin-zinc-polysaccharide complex, which resulted in separation by the increase of temperature. Beverages containing alginate, at 90 °C, displayed the same hue values as the PCW control; however, chroma and luminosity increased, and precipitates were formed in the solution. Lower temperatures were more suitable for analyzing alginate effectiveness as a pigment-protecting agent. Further experiments of long-term stability at room temperature have confirmed the protecting effect of ZnCl2 and alginate. In conclusion, the combination of ZnCl2 with alginate is a promising color stabilization method; however, there is a need to optimize the conditions to stabilize pigments from color corn to be used as natural pigments for different food applications.