Quercetin powder is a natural compound tied to what all of us seek: better longevity, heart health, endurance, immune system and more.Quercetin is a type of flavonoid antioxidant that’s found in plant foods, including leafy greens, tomatoes, berries and broccoli. It’s technically considered a "plant pigment," which is exactly why it’s found in deeply colored, nutrient-packed fruits and veggies. quercetin plays an important part in fighting free radical damage, the effects of aging and inflammation.