I wonder if cooking the apple reduces the amount of quercetin. I eat apples raw and microwaved (with some grape nuts trail mix cereal).

Onions Pack Quercetin Power.

Quercetin, a formidable antioxidant with wide-ranging activity, is concentrated in onions. Studies show that quercetin is anti-cancer, anti-fungal, anti-inflammatory, anti-viral and anti-bacterial. It also helps block the formation of blood clots and processes that lead to artery-clogging. A recent Dutch study found that those who ate half an onion a day cut their risk of stomach cancer in half. In another Dutch study, those eating the most "bioflavonoids," mainly quercetin, were least likely to suffer fatal heart attacks.

For the most quercetin, eat red and yellow onions; white onions have very little. Coming soon: super-potent onions. At the University of Wisconsin and the University of Texas M.D. Anderson Cancer Center, researchers are developing onions extra-high in quercetin and other disease-fighting phytochemicals.

Red wine, broccoli and tea are also rich in quercetin.

Interesting article:

http://www.sciencedirect.com/science...faa1f6ef1f72c8