Thermal kinetics on antiradical capacity of mulberry fruit extract

The effects of temperature and pH on the kinetics of the antiradical capacity of mulberry fruit extract were investigated. The browning index (A₄₂₀/A₅₁₀) increased as pH increased. The change in browning index at pH 2.0 was less than that at pH 4.0. The antiradical capacity increased as browning index increased. The correlation values (slop) of antiradical capacity and browning index were 135.8 (80 °C), 164.4 (90 °C), and 179.7 (100 °C). The antiradical capacity variation was adequately described by both first order and zero order kinetics; however, a zero order kinetic model was proposed because of a better fit. According to the Arrhenius model, the activation energies for antiradical capacity in the range 80–100 °C for the three different pH values were 82.0 kJ/mol for pH 2.0, 70.8 kJ/mol for pH 3.0, and 41.1 kJ/mol for pH 4.0.