Flavonoid content in fresh, home-processed, and light-exposed onions and in dehydrated commercial onion products.
Onion plants synthesize flavonoids as protection against damage by UV radiation and by intracellular hydrogen peroxide. Because flavonoids also exhibit health-promoting effects in humans, a need exists to measure their content in onions and in processed onion products. To contribute to the knowledge about the levels of onion flavonoids, HPLC and LC-MS were used to measure levels of seven quercetin and isorhamnetin glucosides in four Korean commercial onion bulb varieties and their distribution within the onion, in scales of field-grown onions exposed to home processing or to fluorescent light and in 16 commercial dehydrated onion products sold in the United States. Small onions had higher flavonoid content per kilogram than large ones. There was a graduated decrease in the distribution of the flavonoids across an onion bulb from the first (outside) to the seventh (innermost) scale. Commercial, dehydrated onion products contained low amounts or no flavonoids. Losses of onion flavonoids subjected to "cooking" (in percent) ranged as follows: frying, 33; sauteing, 21; boiling, 14-20; steaming, 14; microwaving, 4; baking, 0. Exposure to fluorescent light for 24 and 48 h induced time-dependent increases in the flavonoid content. The results extend the knowledge about the distribution of flavonoids in fresh and processed onions.
Lee
Seung Un
SU
Department of Food Service Industry, Uiduk University, Gangdong, Gyeongju, Gyongbuk, Korea 780-713.
Lee
Jong Ha
JH
Choi
Suk Hyun
SH
Lee
Jin Shik
JS
Ohnisi-Kameyama
Mayumi
M
Kozukue
Nobuyuki
N
Levin
Carol E
CE
Friedman
Mendel
M