Free Radical Scavenging and Leukemia Cell Growth Inhibitory Properties of Onion Powders Treated by Different Heating Processes

Methanol extracts of onion powder dried by hot air (60 °C), vacuum (35 °C), and lyophilization (35 °C) were used to study the effects of drying method on the quercetin composition and the subsequent antioxi‐dative changes. It was found that hot air‐dried onion had higher radical scavenging activities in both DPPH and peroxide radicals than those of the freeze‐ and vacuum‐dried onions. HPLC analyses showed that freeze‐ and vacuum‐dried onions contained more quercetin glycosides, whereas hot air‐dried onion dominated in aglycone. A strong cell proliferation inhibition activity in hot air‐dried onion was observed for leukemia cell lines CEM and U937, whereas freeze‐ and vacuum‐dried onions gave comparatively moderate inhibition. Low cell proliferation inhibition was obtained in 3 dried onions for leukemia cell lines K562, P3HR‐1, and Raji.