The Distribution of Quercetin and Quercetin Glycosides in Vegetable Components of the Human Diet

Identification and quantification of flavonoids in traditional cultivars of red and white onions at harvest

“…_ 1 ) T D $ F I G ] 3 h) of quercetin 4-glucoside into quercetin aglycone can be explained by competitive inhibition of quercetin 4 0 -O-b-glucosidase by quercetin 3,4-diglucoside, a mechanism that explains how the conversion rate of quercetin 4-glucoside to quercetin aglycone is kept low while the concentration of quercetin 3,4-diglucoside remains high (Wegh and Luyten, 1997). Flavonol distribution has been studied in a number of white, yellow and red onion cultivars (Bilyk et al, 1984;Mizuno et al, 1992;Leighton et al, 1993;Patil and Pike, 1995;Tsushida and Suzuki, 1996;Hirota et al, 1998Hirota et al, , 1999Mogren et al, 2007), and the results reported herein are in agreement with the published information. It is suggested that flavonol content increases during aging of cells that constitute scales of onion bulbs, because it is known that cells of the outer scales are more aged than those of the inner scales in a bulb, and that cells in the upper position are older than those in the lower position in a scale.…”