Onion plants make flavonoids to defend themselves from UV radiation and from oxidation by natural hydrogen peroxide. Flavonoids are beneficial to humans. This study was done to evaluate the levels of quercetin and related chemicals in onions.
The beneficial effects of onions are the following: anticarcinogenic, anticholesterol, antidepressant, antidiabetic, antifungal, anti-inflammatory, antimicrobial, antiosteoporotic, antioxidative, antihypertensive and antispasmodic. Flavonoids have an attraction for copper, iron and zinc.
Smaller onions were found to have higher levels of flavonoids than did the larger ones by weight. The small onion bulbs have 2.7 times as much flavonoid as the large onion bulbs, by weight. The outer layers of the onion had higher levels of flavonoids, with the amounts decreasing down to the seventh layer from the outside.
Commercial, dried onions had very low levels of flavonoids. Red onions have more flavonoids than yellow ones; yellow onions have more flavonoids than white ones. Flavonoids are highest in fresh green onions. Lactic fermentation alters onion flavonoid content. Sulfur compounds are responsible for the pungency of onions. More pungent onions have higher flavonoid levels than sweet onions.
Cooking onions resulted in the following percentage loss of flavonoids: frying, 33%; sauteing, 21%; boiling, 14-20%; steaming, 14%; microwaving, 4%; baking, 0%. Exposure of onions to fluorescent lights for 24 and 48 hours increased the amount of flavonoids. Storing onions for 6 months didn’t change their flavonoid content. Dehydrated onion products often have no flavonoids at all.
CONCLUSION: This study increases our knowledge of the flavonoid content of onions.
NOTE: Onions are known, scientifically, as Allium cepa. Read about red onion peel as herbal viagra.
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