Onion is a major source of flavonoids and is cooked in various ways in the world. The major flavonoids in onion are two quercetin glycosides, quercetin 4’-O- β -glucoside (Q4’G) and quercetin 3,4’-O- β -diglucosides (Q3,4’G), which are recognized as bioactive substances that are good for human health.
Onions do not develop their characteristic flavor until their cells are damaged by cutting, slicing, chopping, or cooking.
When onion cells are damaged an enzyme called alliinase is released from compartments within each cell. The enzyme then comes in contact with an odorless compound called isoalliin. The enzyme converts isoalliin into a very unstable volatile compound called 1-propenylsulfenic acid, which is rapidly converted to compounds called thiosulfinates and thiosulfonates that are responsible for the characteristic pungent odor and flavor of raw onions
Yellow Onions are well-suited for any application from raw to cooked. A reliable standby for cooking, they turn a rich, dark brown when caramelized and give French Onion Soup its tangy sweet flavor.
Red Onions with their wonderful color are a good choice for fresh uses like pickling or marinating, and for grilling, charbroiling and roasting.
Chemical
constituents of onion
