Physical characterization of genipin complexes coupled with multivariate data analysis to assess formed pigments

Abstract

The potential of electrophoretic mobility and dynamic light scattering (DLS) was investigated to assess pigment formation in aqueous solution after the genipin reaction with different amino acids by separate. Absorbance, mobility, hydrodynamic size, polydispersity index, and conductivity of the aqueous solutions were measured after the reaction. Only complexes derived from genipin and leucine, tyrosine, arginine, lysine, and glycine developed dark blue colors. From all measured variables, complex size was correlated with their blue color intensity, and darkest blue complexes showed the highest hydrodynamic size (1073–4179 nm). Moreover, size pigments below 1 µm were obtained for all amino acids at different concentrations of genipin and amino acid, except for arginine. A partial least squares (PLS) model for size was built and exhibited a good ability to describe the distribution in blue complexes formed after the reaction of genipin and excess of amino acid (mM): (R2adj = 0.88; RMSE = 0.94). Electrophoretic mobility and DLS coupled with multivariate analysis is a useful tool as it can give reliable assessment of the physical properties of aqueous solutions of genipin pigments.