Study of the reaction between genipin and amino acids, dairy proteins, and milk to form a blue colorant ingredient

[Display omitted] •Reaction mechanisms from the molecular colorant to the genipin-milk protein complex were studied.•Milk is an ideal reaction medium for the blue colorant formation with genipin.•Preferential type and concentration of amino acids and pH medium were discovered.•The effect of protein structure on blue color formation was discussed.•The approximate size of the genipin-protein complex was determined. Currently, one of the biggest challenges of the colorant industry is to obtain natural blue colorants. Among the different options, a blue pigment can be formed by a crosslinking reaction between genipin and primary amine groups. However, at the industrial level, obtaining an ingredient from pure compounds, such as amino acids, is economically unfeasible. The present work aimed to study the reaction and kinetics of the blue color formation, starting the study with pure compounds (genipin and amino acids) to more complex and cheaper natural sources, such as Genipa americana L. fruits and milk. The reaction kinetics of the monomers/dimers for different amino acids reacting with genipin was evaluated, as well as the preferential amino acid, genipin:amino acid ratio and pH, to obtain the most rapid and intense blue color. Finally, the blue pigment formed using milk and its proteins was characterized by SDS-PAGE. The results suggest that the reaction kinetic is influenced by the type and concentration of the amino acid used and the pH of the medium, which could facilitate the further standardization of the industrial process. We also suggested milk as an excellent reaction medium to obtain the colorant from genipin as it presents an ideal pH and favorable amino acid composition to facilitate the reaction.