3-Deoxyanthocyanidins and their derivatives: Modulation of their coloring properties as a function of pH and molecular binding to micelles and biopolymers

Although much less distributed in nature than anthocyanins, 3-deoxyanthocyanidins (3-DAs) and their derivatives are the pigments of the widely grown crop red sorghum. They are also known to be more resistant than common anthocyanins to bleaching by water addition or thermal degradation. Thus, 3-DAs have potential for development as red – pink food colors, but formulations aimed at increasing their water-solubility and color stability remain highly desirable. Looking for 3-DA derivatives with improved and diversified color properties is also an important issue. In this work, apigeninidin (APN), the main 3-DA in red sorghum, and its naturally occurring derivative 10-hydroxyphenyl-pyranoapigeninidin (HP-pAPN, prepared in 70% yield from APN) were investigated for their color properties, once solubilized by interactions with proteins (bovine serum albumin, β-lactoglobulin), oligo-/polysaccharides (β-cyclodextrin, pectin) or surfactants (Brij35, CTAC). Beside providing water solubility, the different matrices are shown to modulate the color of APN and HP-pAPN by a combination of charge and hydrophobic effects, some (e.g., β-lactoglobulin, pectin) also improving the resistance of APN to water addition. Remarkably, the anionic base of HP-pAPN, once inserted into positively charged CTAC micelles, expresses an intense pink color that is stable over weeks in near neutral solution. It is also shown that APN readily evolves through oligomerization upon heating and that the oligomer distribution is distinct from the one observed in red sorghum.