Response Surface Optimization of Flavonoid Extraction and in Vitro Antioxidant Activity of Extract from Dendrobium Chrysotoxum Lindl. Flowers

  Objective  Extraction process of flavonoids from the flowers of Dendrobium chrysotoxum Lindl. was optimized, and the antioxidative activity of the extract determined in vitro.

  Method  Flowers of D. chrysotoxum was subjected to an ethanol extraction for flavonoids. The resulting yield was weighed against the processing conditions based on the single-factor tests and Box-Benhnken center composite experiment with four factors including ethanol volume fraction, solvent-to-substrate ratio, temperature, and time of ultrasonic treatment. The antioxidant capacity was estimated by the ability of the extract to scavenge 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl free radicals.

  Result  The optimized processing conditions were determined to include ethanol volume fraction at 83%, solvent-to-substrate ratio at 31 mL·g^-1, temperature at 59℃ and ultrasound application for 44m to obtain up to 9.71 mg·g^-1 of total flavonoids in the extract. The yield exceeded the theoretically expected 9.60 mg·g^-1 with a relative deviation of 1.15%. The in vitro tests showed an IC₅₀ for DPPH to be 11.30 μg·mL^-1, a scavenging ability 0.51-time of L-ascorbic acid or 1.42-time of BHT, while that for hydroxyl radicals, 137.26 μg·mL^-1, a scavenging ability 0.70-time of L-ascorbic acid or 1.95-time of BHT.

  Conclusion  The optimized flavonoid extraction paved the way for scale-up utilization of D. chrysotoxum flowers.