Abstract: Total flavonoids in propolis were extracted with ethanol and the antioxidant capacity of propolis extract was evaluated. The major factors that affect antioxidant stability were identified as ethanol concentration, extraction time, extraction temperature and material-to-liquid ratio and their effects of the extraction efficiency of total flavonoids were evaluated using an L9 (34) orthogonal array design to determine optimal conditions for the extraction of total flavonoids from propolis. The antioxidant stability of propolis extract was evaluated by measuring the scavenging capacity against hydroxyl free radicals under various conditions of pH, temperature, metal ions and illumination. The optimal extraction conditions were ethanol concentration of 80%, extraction temperature of 80 ℃, material-to-liquid ratio of 1:10 and extraction duration of 2 h. The propolis extract was relatively stable in the presence of metal ions such as Na+, K+, Ca2+ or weak acid, while poor antioxidant stability of propolis extract was observed in the presence of strong acid, strong alkali, light or heat.

Key words: propolis, flavonoids, antioxidant, stability