Effect of storage and domestic processing on the content and composition of flavonol glucosides in onion (Allium cepa)

The stability of the major flavonol glucosides, quercetin 3,4'-O-diglucoside (QDG) and quercetin 4'-O-monoglucoside (QMG), was studied in two varieties of onion (Red Baron and Crossbow) that were cured and stored for 6 months under normal commercial conditons and analyzed at; regular intervals. Onions were also cooked by boiling in water and by frying in oil under normal domestic conditions. Apart from a 50% loss of quercetin 4'-O-monoglucoside during the initial drying process, little change in content and composition was observed over 6 months of storage. Neither boiling nor frying resulted in interconversion of the quercetin conjugates or production of free quercetin, although a 25% loss overall was recorded for each process.