ANALYTICAL PROBLEMS IN THE STUDY OF FLAVONOID COMPOUNDS IN ONIONS

Flavonoids, although potentially mutagenic, are widely thought to have beneficial effects in the diet resulting from their antioxidant and m etal binding properties. Epidemiological evidence correlates diets ric h in flavonoid compounds with a low risk of coronary heart disease. In the present work flavonoids (principally flavonols and anthocyanins) are studied in the onion, a major dietary source of flavonoids. This w ork concentrates on the development of methods to study flavonoids in their natural form in plant foods as conjugates. Two major components quercetin monoglucoside and quercetin diglucoside account for 80% of t he total flavonoids in onions. Anthocyanins are only minor components of the flavonoid spectrum in the edible portion of red varieties. A pr eliminary study of flavonols in onions, which had been finely chopped, suggests that in most varieties there is only a small loss in total f lavonol but that there is a progressive loss of the diglucoside compon ent with an accompanying quantitative accumulation of the monoglucosid e and the aglycone. Copyright (C) 1996 Elsevier Science Ltd