Table of Contents Hide
- Onions Nutritional Profile
- How Many Nutrients in This Food
- How To Serve Nutritious Food
- Diets That May Restrict or Exclude This Food
- How ToBuying This Food
- How To Storing This Food
- How To Preparing This Food
- What Happens When You Cook This Food
- How Other Kinds of Processing Affect This Food
- Adverse Effects Associated with This Food
- Onions Interactions Food/Drug
(Chives, leeks, scallions [green onions], shallots)
See also Garlic.
Onions Nutritional Profile
• Energy value (calories per serving): Low
• Protein: Moderate
• Fat: Low
• Saturated fat: Low
• Cholesterol: None
• Carbohydrates: High
• Fiber: Moderate
• Sodium: Low
• Major vitamin contribution: Folate, vitamin C
• Major mineral contribution: Calcium, iron
How Many Nutrients in This Food
• All onions are high in dietary fiber and a good source of the B vitamin folate and vitamin C. Immature onions known as scallions, if they are picked before the bulbs have fully developed, or green onions or spring onions, if they are picked with large bulbs have moderate amounts of vitamin A derived from deep yellow carotenes masked by green chlorophyll pigments in the green tops.
• Red onions are colored with red anthocyanins; shallots, yellow onions, white onions, and the white bulbs of the leeks, green onions, ramps [wild leeks], and scallions are colored with creamy pale yellow anthoxan thins. Neither anthocyanin nor anthoaxanthins provide vitamin A.
• One-half cup chopped white or yellow onion has 1.4 g dietary fiber and 5.9 mg vitamin C (13 percent of the RDA for a woman, 14 percent of
the RDA for a man).
• One-half cup chopped green onions, a.k.a. scallions (bulb and leaves), has 1.3 g dietary fiber, 498 IU vitamin A (22 percent of the RDA for a woman, 17 percent of the RDA for a man), and 9.4 mg vitamin C (13 percent of the RDA for a woman, 10 percent of the RDA for a man).
How To Serve Nutritious Food
• Whole fresh green onions or green onions chopped (green portions and all) and added to a salad or other dish.
Diets That May Restrict or Exclude This Food
• Antiflatulence diet
• Low-fiber diet
How ToBuying This Food
Firm, clean shallots; yellow, white, or red onions with smooth, dry, crisp skin free of any black mold spots. Leeks and green onions should have crisp green tops and clean white bulbs.
Onions that are sprouting or soft or whose skin is wet—all signs of internal decay.
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How To Storing This Food
• Store shallots and red, yellow, and white onions in a cool cabinet room or root cellar where the temperature is 60°F or lower and there is plenty of circulating air to keep the onions dry and prevent them from sprouting.
• Properly stored, onions should stay fresh for three to four weeks; at 55°F they may retain all their vitamin C for as long as six months. Cut the roots from green onions, scallions, and leeks; trim off any damaged tops; and refrigerate the vegetables in a tightly closed plastic bag. Check daily and remove tops that have wilted.
How To Preparing This Food
• When you cut into an onion, you tear its cell walls and release a sulfur compound called pro-panethial-S-oxide that floats up into the air. The chemical, identified in 1985 by researchers at the University of St. Louis (Missouri), turns into sulfuric acid when it comes into contact with water, which is why it stings if it gets into your eyes. You can prevent this by slicing fresh onions under running water, diluting the propanethial-S-oxide before it can float up into the air.
• Another way to inactivate propanethial-S-oxide is to chill the onion in the refrigerator for an hour or so before you slice it. The cold temperature slows the movement of the atoms in the sulfur compound so that they do not float up into the air around your eyes.
• To peel the brown papery outer skin from an onion or a shallot, heat the vegetable in boiling water, then lift it out with a slotted spoon and put it in cold water. The skin should come off easily.
What Happens When You Cook This Food
• Heat converts an onion’s sulfurous flavor and aroma compounds into sugars, which is why cooked onions taste sweet. When you “brown” onions, the sugars and amino acids on their surface caramelize to a deep rich brown and the flavor intensifies. This browning of sugars and amino acids is called the Maillard reaction, after the French chemist who first identified it.
• Onions may also change color when cooked. Onions get their creamy color from anthoxanthins, pale-yellow pigments that turn brown if they combine with metal ions. (That’s why onions discolor if you cook them in an aluminum or iron pot or slice them with a carbon-steel knife.) Red onions contain anthocyanin pigments that turn redder in acid (lemon juice, vinegar) and bluish in a basic (alkaline) solution.
• And the chlorophyll molecules that make the tops of green onions green are sensitive to acids. When heated, chlorophyll reacts with acids in the vegetable or in the cooking water to produce pheophytin, which is brown. The pheophytin makes green onion tops olive-drab.
• To keep green onions green, you have to reduce the interaction between the chlorophyll and the acids. You can do this by leaving the top off the pot so that the acids float off into the air or by steaming the onions in little or no water or by cooking them so quickly that there is no time for the reaction to occur.
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How Other Kinds of Processing Affect This Food
Drying onions into flakes removes the moisture and concentrate the nutrients. Ounce for ounce, dried onions have approximately nine times the vitamin C, eight times the thiamin, ten times the riboflavin, nine times the niacin, five times the iron, and eleven times as much potassium as fresh onions.
Adverse Effects Associated with This Food
The onion’s sulfur compounds can leave a penetrating odor on your breath unless you brush after eating. Fresh onions are smellier than cooked ones, since cooking breaks down the sulfur compounds.
Onions Interactions Food/Drug
Green Onions are rich in vitamin K, the blood-clotting vitamin produced naturally by bacteria in the intestines. Consuming large quantities of this food may reduce the effectiveness of anticoagulants (blood thinners) such as warfarin (Coumadin). One chopped, raw green onion (top and bulbs) contains 207 mcg vitamin K, more than three times the RDA for a healthy adult.
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