Hansen Pure Quercetin powder, 50 gQuercetin is a plant flavanol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, seeds and grains; red onions and tusks are common foods containing a considerable amount of quercetin. Quercetin has a yellow color and a bitter taste. She has antioxidant properties and protects the body from free radicals which are unstable molecules in the body that they can increase the risk of disease and accelerate aging.