Flavonoids and organosulfur compounds are the two major classes of secondary metabolites found in onions that are believed to play a role as health-promoting, disease-preventing dietary supplements, including antioxidant activity. In this book, the authors present topical research in the study of onion consumption and health effects. Topics include an overview on the bioactivity of onions; an ultrasound-assisted flavonoid extraction from onions; and the physiological attributes of GST, Gly I, Gly II and allinase in onion bulbs and cultured cells.