Effect of light and sweeteners on color in an amaretto-type liqueur

Studies on the color loss in an amaretto-type liqueur under controlled light conditions showed a clear dependence of the decoloration rate on the light intensity, and complete color stability in the absence of light. The principal sweetener used in the preparation of the liqueur strongly affected the rate of color loss under irradiation, color stability being much greater for the formulations containing sucrose or no added sweetener instead of fructose 42. These differences were more pronounced in experiments conducted with chemically well-defined mixtures that contained either of the 2 azo dyes used in the coloration of the amaretto, tartrazine, and Allura Red, and various alternative sweeteners, in 28% (v/v) ethanol solution: D-fructose and, to a lesser extent, D-glucose, at concentrations of 14% (w/v), were effective in bringing about photodecoloration, while no color loss was detected in the presence of sucrose, or in the absence of any added sugar. The results are interpreted in terms of a redox reaction of reducing sugars with the diarylazo compounds, the function of the light being the conversion of the azo compound from the predominant trans configuration to the cis configuration, which on geometric grounds lends itself better to a concerted, cyclical redox reaction with the reducing sugar.