Bathochromic and Hyperchromic Effects of Aluminum Salt Complexation by Anthocyanins from Edible Sources for Blue Color Development

Use of artificial food colorants has declined due to health concerns and consumer demand, making natural alternatives a high demand. The effects of Al(3+) salt on food source anthocyanins were evaluated with the objective to better understand blue color development of metalloanthocyanins. This is one of the first known studies to evaluate the effects of food source anthocyanin structures, including acylation, with chelation of aluminum. Cyanidin and delphinidin derivatives from different plants were treated with factorial excess of Al(3+) in pH 3-6 and evaluated by spectrophotometry and colorimetry over 28 days. Anthocyanin concentration, salt ratio, and pH determined final color and intensity. Pyrogallol moieties on delphinidin showed furthest bathochromic shifts, whereas acylation promoted higher chroma. Blue color developed at lower pH when acylated anthocyanins reacted with Al(3+); hue ∼270 occurred with acylated delphinidin at pH ≥ 2.5. Highest chelate stability was found with AlCl3100-500× anthocyanin concentration. This investigation showed anthocyanin-metal chelation can produce a variety of intense violet to blue colors under acidic pH with potential for food use.