Heat and light stability of natural yellow colourants in model beverage systems

The performance of 10 natural yellow colourants at different concentrations (0.001-0.3% w/v) was investigated in a model beverage system at various pH levels (3.5, 5.5 and 7.5) containing 10% w/v of sucrose, with or without ethanol (15% v/v) to simulate both alcoholic and non-alcoholic lemon-like beverages. Thus, the incidence of pH, ethanol and colourant concentration on spectral properties as well as turbidity were evaluated. The λ_max was found to be independent from concentration in the tested range (0.001- 0.3% w/v), whereas the specific absorbance at λ_max increased linearly. Moreover, the absorption spectrum and λ_max of yellow pigments were found to be independent of pH and ethanol. Gardenia, safflower, and curcumin had the highest colour intensity and the lowest turbidity level. Heat and light stability were studied for these as well. Safflower was found to be the most stable colourant against heat (25, 40, 60, 80°C) and light (550 W/m², 30°C).