Reevaluation of Physical and Chemical Singlet Oxygen Quenching Efficiency of Antioxidants via a Specific Methanol-Soluble Trap

Furfuryl alcohol (FFA), a methanol-soluble and highly specific compound for singlet oxygen (1O2), was used as a 1O2 trapping agent to reevaluate physical and chemical 1O2 quenching efficiency of five antioxidants, namely α-tocopherol, butylated hydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), epigallocatechin gallate (EGCG), and quercetin. The total 1O2 quenching rate constants of α-tocopherol, BHA, TBHQ, EGCG, and quercetin were 2.0 (±0.1) × 109, 1.1 (±0.1) × 108, 5.6 (±0.3) × 108, 4.1 (±0.1) × 108, and 2.2 (±0.1) × 108 M−1s−1, respectively. The chemical quenching rate constants of α-tocopherol, BHA, TBHQ, EGCG, and quercetin were 1.4 × 107, 2.0 × 106, 7.7 × 106, 2.0 × 107, and 7.9 × 106 M−1s−1, respectively. The percentages of chemical quenching in total 1O2 quenching were 0.7%, 1.8%, 1.4%, 4.8%, and 3.6% for α-tocopherol, BHA, TBHQ, EGCG, and quercetin, respectively, indicating that the five antioxidants quenched 1O2 almost exclusively by a physical quenching mechanism. This is the first report on the 1O2 quenching mechanism of quercetin in methanol solvent. The results of this study will provide theoretical guidance for the application of antioxidants to inhibit edible oil or fat-containing food from photooxidation.