Synergistic Effects of Astaxanthin and Chlorophyll <i>a</i> on Singlet Oxygen Quenching Reinforced by Calcium Ascorbate

This study examines the synergistic effects of astaxanthin and chlorophyll a in quenching singlet oxygen (1O2). The 1O2 quenching rate constant of chlorophyll a is 1.72 × 1010 M–1 s–1, but it increases to 3.17 × 1010 M–1 s–1 in the presence of astaxanthin. The strongest synergistic effect occurs at a molar ratio of astaxanthin:chlorophyll a = 1:2. 1H NMR analysis revealed shifts in signals and changes in the longitudinal relaxation time (T1) of astaxanthin upon the addition of chlorophyll a, indicating their proximity and interaction, which were also supported by fluorescence quenching analysis. Further addition of 150 equimolar calcium ascorbate protects more than 95% of both antioxidants from thermal decomposition (60 °C, 1 h). The optimal molar ratio of astaxanthin, chlorophyll a, and calcium ascorbate is 1:2:150, maximizing the synergistic effect of astaxanthin and chlorophyll a, while calcium ascorbate reinforces 1O2 quenching by providing a reductive environment and long-term stability.