GSTM1 genotypes have a significant effect on the metabolism of sulforaphane derived from standard or high-glucosinolate broccoli. It is possible that the difference in metabolism may explain the greater protection that GSTM1-positive persons gain from consuming broccoli. The potential consequences of consuming glucosinolate-enriched broccoli for GSTM1-null and -positive persons are discussed.

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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. Keywords: Onion; Allium cepa; flavonol; quercetin; glucoside; HPLC; storage; processing