Bioavailability of Quercetin Glucosides in Onion. Kana Ioku. Laboratory of Food Science, Development of Home Economics, Faculty of Education, Osaka Kyoiku.
Foods Food Ingredients J. Japan No. 201 (2002)
Bioavailability of Quercetin Glucosides in Onion Kana Ioku Laboratory of Food Science, Development of Home Economics, Faculty of Education, Osaka Kyoiku University 4-698-1, Asahigaoka, Kashiwara, Osaka 582-8582, Japan Summary Fravonoids are widely found in plant foods and beverages such as tea and wine. The intake of flavonoids in Japan is very high compared with other countries. Recently, it has been stated that flavonoids may play an important role in the prevention of life-style-related diseases. And, it is recognized that flavonoids are one of the important functional compounds in foods. Onion is a good source of flavonoids. Major flavonoids in onion are quercetin compounds, quercetin-3,4’-diglucosides and quercetin-4’-gluciside. Short-term ingestion of onion demonstrated that humans absorb part of the quercetin glucosides present in their diet and accumulate them as quercetin conjugates exclusively in the blood plasma. Various cooking methods, such as frying and boiling, do not cause the degradation of quercetin conjugates when cooking onion. Furthermore, the remarkable increase of quercetin on the basis of the hydrolysis of quercetin glucosides was not observed. Dietary quercetin glucosides in onion are primarily hydrolyzed and liberated aglycones in the jejunum. There are many isomers with quercetin glycosides in foods. It was suggested that the sugar moiety in quercetin glycosides affects their bioavailability of quercetin glucoside is better than its glycoside. Some flavonoid glycosides are hydrolyzed by anaerobic nitrobacteria in the large intestine.
