Comparative analysis of flavonoids extracted from Dendrobium chrysotoxum flowers by supercritical fluid extraction and ultrasonic cold extraction

Flowers are by-products of the medicinal plant Dendrobium chrysotoxum, with high yield but low utilization rate. Extracting flavonoids from D. chrysotoxum flowers can not only reduce resource waste but also bring economic benefits. In this study, two green extraction methods, SFE (supercritical fluid extraction) and UCE (ultrasonic cold extraction) were used to extract flavonoids from D. chrysotoxum flowers, and the response surface method (RSM) was used to optimize the extraction conditions. The results showed that on the optimal conditions of SFE (time 90 min, temperature 50 °C, pressure 20 MPa) and UCE (time 30 min, power 400 W, temperature 40 °C, solid-liquid ratio 1:40 (w:v), ethanol concentration 60%), the total flavonoid extraction yield was 2.04% ± 0.02% and 0.64% ± 0.02%, respectively. In vitro, antioxidant activity analysis showed that both extracts had good antioxidant activity, and the antioxidant activity of SFE extract was higher than that of UCE extract. The quantitative determination of flavonoid compounds showed that the content of quercetin, kaempferol, and catechin in SFE extract was significantly higher than that in UCE extract, and the content of ellagic acid in the two extracts was similar. These results indicated that the two green extraction methods improved the resource utilization of D. chrysotoxum flowers, and SFE was more suitable for extracting flavonoids from D. chrysotoxum flowers than UCE.