Abstract:The effects of different organic acids on the pigmentation and thermal stability of anthocyanins from mulberries were investigated. First, UPLC-MS/MS was used to analyze the composition of mulberry anthocyanins. Then, 4-hydroxybenzoic acid, protocatechuic acid, gallic acid, chlorogenic acid, and malic acid were used as co-pigments to determine the influence of pH, temperature, and organic acid concentration on the pigmentation of the mulberry anthocyanins. The thermal degradation of anthocyanins in food was simulated in water baths at 60, 70 and 80 ℃ to explore the effects of the organic acids on the thermal degradation kinetics of the mulberry anthocyanins. The most significant color enhancement and red-shifting effects were observed at anorganic acid concentration of 960 mg/L, pH of 3.5, and temperature of 20 ℃. The co-pigmentation effects of the five organic acids were in the following order: malic acid>chlorogenic acid>gallic acid>protocatechuic acid>4-hydroxybenzoic acid. Compared with that of the blank group, the absorbance at λmax of the group treated with malic acid increased by 45.04%. The stoichiometric ratio (n), equilibrium constant (K), and Gibbs free energy (ΔG°) indicated that the co-pigmentation reactions were all spontaneous. Malic acid, demonstrating the best co-pigmentation effect, had the largest K value (26.85) and the smallest ΔG° value (-8.02 kJ/mol). Through degradation experiments, it was found that the addition of organic acids could prolong the half-life (T1/2) of the anthocyanins and reduce their degradation constant (k). At 60 ℃, gallic acid prolonged the T1/2 of the anthocyanins from 17.50 h to 26.23 h and reduced the k value from 6.6×102 min-1 to 4.4×102 min-1. Therefore, co-pigmentation with organic acids can effectively improve the stability of anthocyanins from mulberries.
