Effect of Processed Onions on the Plasma Concentration of Quercetin in Rats and Humans.

Unlabelled: Onion is a major dietary source of the bioactive flavonoid, quercetin. Quercetin aglycone (QA) is exclusively distributed in the onion peel, although quercetin-4'-β-O-glucoside (Q4'G) is present in both the peel and the bulb, and quercetin-3,4'-β-O-diglucoside (Q3,4'diG) is present only the bulb. The bioavailability of flavonoids from fruits and vegetables is frequently affected by the manufacturing process and related conditions.

Plasma HDL reduces nonesterified fatty acid hydroperoxides originating from oxidized LDL: a mechanism for its antioxidant ability.

The antioxidant property of plasma high-density lipoprotein (HDL) is thought to be involved in potential anti-atherogenic effects but the exact mechanism is not known. We aimed to reveal the contribution of HDL on the elimination of lipid hydroperoxides (LOOH) derived from oxidized low-density lipoprotein (LDL). Oxidized LDL prepared by copper ion-induced oxidation contained nonesterified fatty acid hydroperoxides (FFA-OOH) and lysophosphatidylcholine (lysoPtdCho), in addition to cholesteryl ester hydroperoxides (CE-OOH) and phosphatidylcholine hydroperoxides (PtdCho-OOH).

alpha-Oligoglucosylation of a sugar moiety enhances the bioavailability of quercetin glucosides in humans.

Dietary intake of quercetin is suggested to be potentially beneficial for the prevention of various diseases. We examined the effect of alpha-oligoglucosylation of the sugar moiety of quercetin monoglucoside on its bioavailability in humans. Enzymatically modified isoquercitrin (EMIQ) was prepared by enzymatic deglycosylation and the subsequent of alpha-oligoglucosylation of quercetin 3-O-beta-rutinode (rutin).