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 metal binding properties. Epidemiological evidence correlates diets rich 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 work 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 the total flavonoids in onions. Anthocyanins are only minor components of the flavonoid spectrum in the edible portion of red varieties. A preliminary study of flavonols in onions, which had been finely chopped, suggests that in most varieties there is only a small loss in total flavonol but that there is a progressive loss of the diglucoside component with an accompanying quantitative accumulation of the monoglucoside and the aglycone.