Abstract: Seven phenolic compounds and organic acids (epicatechin, caffeic acid, rosmarinic acid, chlorogenic acid, oxalic acid, malic acid and clove acid) were evaluated in this study for their effects on the color stability of black rice anthocyanins at pH 3.0 and 5.0. The best co-pigment was selected by virtue of its co-pigmentation and thermal stabilization effects on black rice anthocyanins, and its best concentration was explored at pH 3.0. Afterwards, its underlying mechanism of action was investigated by Fourier transform infrared (FTIR) spectroscopy, molecular docking and molecular simulation. The results showed that all the co-pigments except malic acid had good co-pigmentation effect and could improve the thermal stability of black rice anthocyanins at pH 3.0 and 5.0, among which rosmarinic acid at pH 3.0 had the best effect. The co-pigmentation effect increased with increasing concentration of rosmarinic acid from 0.1 to 4.0 mg/mL. Rosmarinic acid showed the best protective effect on the thermal stability of black rice anthocyanins when used at 2.0 mg/mL. The results of FTIR spectroscopy, molecular docking, and molecular simulation revealed that rosmarinic acid could bind to anthocyanins through hydrogen bonds and π-π stacking interactions, which improved the stability of black rice anthocyanins.

Key words: black rice anthocyanins; co-pigments; rosmarinic acid; color stability; molecular dynamics simulation