Quercetin is a highly potent bioflavonoid found in a variety of foods. It is also a building block for flavonoids. It is found in many foods, including onions (especially red), apples, tea, nuts, various types of berries, cauliflower and cabbage. Quercetin has strong antioxidant properties, like other bioflavonoids, and has the ability to stabilize cell membranes. These advantages contribute to the proper functioning of the body's defense mechanisms