Abstract: Proanthocyanidins were extracted from black wattle bark by the ultrasonic technology and purified on AB-8 resin. The oligomers were extracted with ethyl acetate and polymers in water were degraded by H₂SO₃. Finally, the scavenging activities on 2,2-diphenyl-1-picrylhydrazyl free radical (DPPH·) of each fraction were determined. The results showed that the mass fraction of proanthocyanidins in crude extraction increased from 36.2% to 50.4% by purification on AB-8 resin. The recovery was 90.3%. The proanthocyanidins were degraded by H₂SO₃ significantly and the average degree of polymerization drop to 6.25 from 8.11 after degradation. It was found that the proanthocyanidins after degradation had higher DPPH scavenging activity and EC₅₀reduced from 2.25% to 1.88%.

Key words: proanthocyanidins, purification, degradation, DPPH free radical