Abstract:

The extraction of flavonoids from the leaves and stems of Rubus caesius L. was optimized by single factor
experiments and an orthogonal array design. Antioxidant activity of flavonoids extracts was determined by 2,2’-azinobis-(3-
ethylbenzthiazoline-6-sulphonate) (ABTS), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays. The optimal
extraction conditions for total flavonoids were determined as follows: 80 ℃, 70 min, and 60% ethanol as the extraction
solvent with a solid-to-liquid ratio of 1:90 (g/mL). By comparing the adsorption and separation efficiencies of flavonoids
with 14 different macroporous resins, AB-8 resin was selected as the most efficient adsorbent as it had the best adsorption
and desorption capacity for flavonoids from R. caesius L. By single factor experiments, the optimal purification conditions
for crude flavonoids from R. caesius L. leaves and stems were established as follows: sample loading flow rate, 1 mL/min;
flavonoids concentration of sample, 0.32 mg/mL; sample volume, 80 mL; desorption solvent, 40 mL of 60% ethanol; and
desorption flow rate, 1.5 mL/min. After being separated and purified by AB-8 resin, both total flavonoids content and total
antioxidant capacity were significantly improved. The total flavonoids contents from leaves and stems were increased by 1.4
and 2.4 times, the ABTS radical scavenging rates by 1.7 and 2.5 times, and the DPPH radical scavenging rates by 1.7 and 2.6
times, respectively. These results demonstrate that the leaves and stems of R. caesius L. have high flavonoids contents and
antioxidant activity, and can be potential sources of natural antioxidants.

Key words: Rubus caesius L., flavonoids, extraction and purification, antioxidant activity