No abstract

Antioxidant activity and flavonoid content of Welsh onion (Allium fistulosum) (green-leafy and whitesheath varieties) and the e#ect of thermal treatment on them were studied by comparing with those of onion (Allium cepa) (yellow and red varieties). Antioxidant activity was measured by Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP) assays. The order of these indices of antioxidant activity was red onion῍yellow onionῌgreen Welsh onion῎white Welsh onion. The order of the total flavonoid content was red onion῍yellow onion῍green Welsh onion῎white Welsh onion. Major flavonoid of yellow and red onions was quercetin, and that of green Welsh onion was kaempferol. Antioxidant activity of green Welsh onion was increased, but that of the other three vegetables was decreased during boiling for more than +/ minutes. Flavonoids in green Welsh onion were less stable than those in the other three vegetables during the boiling procedure. These results suggested that green Welsh onion, but not the white one, is a potent antioxidant food comparable to yellow onion, and is a good source of kaempferol. Increased antioxidant activity and decreased flavonoid content during boiling were characteristics of green Welsh onion.

The effects of Welsh onion on the development of hypertension and autoxidation were studied in 6-week-old male Sprague-Dawley rats. The rats were fed with a control diet or a high-fat high-sucrose (HFS) diet with or without 5% Welsh onion (green-leafy type or white-sheath type) for 4 weeks. The systolic blood pressure was elevated and the thiobarbituric acid reactive substances (TBARS) in plasma were increased in the rats fed with the HFS diet without Welsh onion. The rats fed with the HFS diet containing Welsh onion, especially the green-leafy type, had lower blood pressure. They also had a higher level of nitric oxide (NO) metabolites in both the urine and plasma, lower activity of NADH/NADPH oxidase in the aorta, and suppressed angiotensin II production. The effect of white Welsh onion on decreasing the blood pressure was not significant, although the effects on increasing NO metabolites in the urine and decreasing NADH oxidase activity in the aorta were significant. The TBARS value in the plasma was lowered in the rats fed with either green or white Welsh onion, but the in vitro radical scavenging and ferric reducing antioxidative activities were much higher with green Welsh onion than with the white type. These results suggest that the green-leafy Welsh onion, but not the white type, reduced superoxide generation by suppressing the angiotensine II production and then the NADH/NADPH oxidase activity, increasing the NO availability in the aorta, and consequently lowering the blood pressure in the rats fed with the HFS diet. The radical scavenging and reducing antioxidative activities of green Welsh onion may also be effective in decreasing superoxide.

The physiological effects of red Welsh onion were examined and compared with those of white Welsh onion. Male 6-week-old spontaneously hypertensive rat (SHR) was fed a control diet or diets high in fat and sucrose (HFS) with or without 5 % Welsh onion (red or white variety) for 4 weeks. A significant effect to suppress the increase in the blood pressure and the increase in the lipids in plasma and liver was observed in rats fed the red, but not white, Welsh onion compared to the rats fed the HFS diets. Red and white Welsh onion was effective to suppress the increase in the lipid peroxides in plasma, and in liver in case of white Welsh onion. The activity of antioxidant enzymes was downregulated by feeding the red and white Welsh onion. These results suggest that, although the antioxidant activity of red Welsh onion is weaker than the white one, antioxidant activity together with hypolipidemic effect of red Welsh onion might work favorably to suppress the increase in blood pressure. Detection of flavonoids, especially quercetin, and anthocyanins suggests that these compounds might be physiologically active components in red Welsh onion.