Kinetic, thermodynamic, and colorimetric study of anthocyanin colorants from bluish fruits: Blueberry, blackberry, and red grape.

This study compared the colorimetric, kinetic and thermodynamic properties of semi-purified anthocyanin colorants from blueberry, blackberry and red grape under acidic conditions (pH 2.0 to 5.0). The extracts were characterized by HPLC-DAD-MS and their compositional differences were considered in relation to hydration kinetics, equilibrium parameters and CIELAB color expression. At pH 3.0, blackberry extract showed the highest chromatic intensity (C*ab = 34.64) and the largest hue angle (hab = 15.89°), while blueberry and red grape colorants remained in the red-purple region (hab = 0.65-2.05°). As pH increased, all colorants exhibited substantial losses of visible absorbance and chroma, reflecting the shift of the flavylium cation to less colored or colorless forms. Kinetic analysis showed the slowest hydration rate for blueberry (kₕ = 0.045 s-1) and the fastest for blackberry (0.077 s-1), while red grape extracts displayed intermediate behavior. Because the process is reversible, the overall kinetic response was interpreted by considering both the forward and reverse contributions rather than kh alone. Thermodynamic differences were less pronounced, but equilibrium data indicated that grape extracts retained color more effectively at high pH values. Overall, the semi-purified colorants differed in the balance between initial color intensity, reversible hydration-related response, and equilibrium color persistence, supporting the combined use of compositional, kinetic, thermodynamic, and colorimetric descriptors for selecting natural anthocyanin colorants for acidic food applications.