Interactions of Natural Flavones with Iron Are Affected by 7- O -Glycosylation, but Not by Additional 6″- O- Acylation.

In iron-fortified bouillon, reactivity of the iron ion with (acylated) flavone glycosides from herbs can affect product color and bioavailability of iron. This study investigates the influence of 7- O -glycosylation and additional 6″- O -acetylation or 6″- O -malonylation of flavones on their interaction with iron. Nine (6″- O -acylated) flavone 7- O -apiosylglucosides were purified from celery ( Apium graveolens ), and their structures were elucidated by mass spectrometry (MS) and nuclear magnetic resonance (NMR). In the presence of iron, a bathochromic shift and darker color were observed for the 7- O -apiosylglucosides compared to the aglycon of flavones that only possess the 4-5 site. Thus, the ability of iron to coordinate to the flavone 4-5 site is increased by 7- O -glycosylation. For flavones with an additional 3'-4' site, less discoloration was observed for the 7- O -apiosylglucoside compared to the aglycon. Additional 6″- O -acylation did not affect the color. These findings indicate that model systems used to study discoloration in iron-fortified foods should also comprise (acylated) glycosides of flavonoids.