Solgar's Quercetin Complex includes the important bioflavonoid Quercetin in a synergistic formula with Ester-C? Plus and Bromelain to provide unique antioxidants as well as immune health support. Quercetin is found in onions and other foods. It possesses antioxidant properties which help to stabilize cell membranes. Ester-C? Plus provides a patented, pH neutral (non acidic), form of vitamin C that is gentle on the stomach. Ester-C? Plus offers the additional benefits of incorporating acerola berry, citrus bioflavonoids, rutin and rose hips. This formula also features bromelain, a natural enzyme derived from pineapple.*