Abstract: The ethanol extracts of abandoned hop branches and leaves of SA-1 and Marco Polo hop varieties grown in Xinjiang were separated by using different polar solvents. The antioxidant activities of the resulting extracts were studied by four in vitro assays: hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl radical, β-carotene-linoleic acid and phosphomolybdenum model systems and were correlated with the contents of polyphenols and flavonoids. The results showed that all samples displayed antioxidant activity. Ethyl acetate extracts from hop main stems, side stems, and leaves had the highest contents of phenols and flavonoids, which were 5.80–34.20 and 2.00–18.00 mg/g, respectively. On the contrary, water extracts had the lowest contents of phenols and flavonoids, which were 0.73–11.05 and 0.06–5.74 mg/g, respectively. The correlation analysis showed that hop main stems, side stems and leaves exhibited significant relationship between antioxidant activity and the contents of phenols and flavonoids (P < 0.05).

Key words: hop, abandoned branches and leaves, polyphenols, flavonoids, antioxidant activity, correlation