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Extending the stability of red and blue colors of malvidin-3-glucoside-lipophilic derivatives in the presence of SDS micelles
Publication . Mendoza, Johan; Pina, Fernando; Basílio, Nuno; Guimarães, Marta; de Freitas, Victor; Cruz, Luís; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier
Anthocyanins lipophilization recently emerged as an efficient tool to deliver oil-soluble dyes aiming to expand their applications in lipophilic matrices such as cosmetics formulations. Sodium dodecyl sulfate (SDS) micelles were used to solubilize malvidin-3-glucoside derivatives bearing an ester chain derived from dodecanoic and hexanoic fatty acids. Detailed investigations on the kinetic and thermodynamic behavior of the pigments towards pH variations was carried out by means of UV-Vis spectroscopy. It was found that the pH domain of the red flavylium cation is extended in ca 0.3–0.4 pH units. The mole fraction of the quinoidal base at neutral conditions increased by 40% when compared with malvidin-3-glucoside in the same micellar media, which provides a great blue color stabilization. The results presented herein report for the first time the blue color stabilization of these lipophilic anthocyanin bioactives, opening new application fields as novel colorants for lipid-based foods and cosmetics.
Colour modulation of blue anthocyanin-derivatives. Lignosulfonates as a tool to improve the water solubility of natural blue dyes
Publication . Araújo, Paula; Basílio, Nuno; Azevedo, Joana; Fernandes, Ana; Mateus, Nuno; Pina, Fernando; de Freitas, Victor; Oliveira, Joana; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier
The impact of a lignosulfonate (calcium) (L) on the chromatic features of two anthocyanin-derived bluish dyes (portisin, P and pyranoanthocyanin dimer, PD) was evaluated in aqueous solutions using UV–Visible spectroscopy. It was demonstrated that the interaction between each dye and this macromolecule at pH 1 occurs by two mechanisms, association and copigmentation that are dependent on L concentration. For instance, at low concentrations of L (up to 0.27 μM) it is observed the association of dyes promoted by their complexation with lignin (different molecules of dye are bound to the same binding sites of L). At higher concentrations of L (25 μM), the aggregation of dyes decreases and each molecule is bound to a different site of L resulting in the formation of a charge-transfer complex (copigmentation). Moreover, the titration of both dyes (P and PD) in the presence of L (19 μM) showed a strong stabilization of their pyranoflavylium cation forms revealed by the considerably higher pKa1 (6.6 ± 0.1 and 6.2 ± 0.1 for P and PD, respectively) in the presence of this macromolecule when compared to the values obtained in the absence (pKa1 = 4.61 ± 0.03 and 4.93 ± 0.04). In addition, the water solubility of the dyes in the absence and presence of L was also evaluated by turbidimetry and the results showed that the water soluble lignosulfonate improved the solubility of the dyes over time.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BPD/84805/2012