Preparation of a genipin blue from egg protein and genipin

Genipin blue is a pigment prepared from the reaction of genipin with amino acid. We describe herein a new method used to prepare genipin blue, water-soluble blue pigments, through the reaction of hen egg protein with genipin. The effects of reaction time, reaction temperature, the pH value of the solution and the mass ratio of the reactants on the preparation are studied. One part of genipin reacted with eight parts of hen egg protein (w/w) in water (pH value of reaction system 7.5) at 60°C for 96 h and gave blue pigments with the maximum colour value of 146.2. The blue pigments showed identical absorption activity in UV spectroscopy (λ(max )= 584 nm) to that of gardenia blue pigments, which were prepared from the reaction of genipin with amino acid.