Relationship between chemical structure and antioxidant function of flavonoids

Abstract

Antioxidant activities (including photo-antioxidant activities) of flavonoids were evaluated fundamentally and kinetically for the potential to produce plastic food packages with high antioxidant performance and food safety. Chalcones with two aromatic rings acquire additional another ring by ring-closure in the metabolic pathway of chalcones and form a flavanone (naringenin), with dramatically decreased antioxidant activities. As further metabolism proceeds, naringenin produces various flavonoids, which gradually acquire antioxidant activities comparable to and finally higher than those of chalcones. Therefore, a plant can again form an enhanced antioxidant, especially with photo-antioxidant activities. In general, flavonoids are present in the concentration of 1-10 mmol/dm3 in plants. The metabolite with the highest antioxidant activities, quercetin, was found to protect a plant almost completely in the concentration of 0.5 mmol/dm3 from harmful UV radiation. The complex metabolic pathway of tyrosine or phenylalanine to flavonoids will be partly necessary for the safe photo-synthesis of plants without suffering UV damage. Such flavonoids are expected to be useful for the safe stabilization of petro chemicals, especially food packages.