Generally speaking, freezing helps retain the nutrient content of fruits and vegetables. But be careful not to boil the water or actually cook the lemons which can reduce the amount of vitamin C and diminish their nutrients. Just be aware that when ascorbic acid levels are high in the blood for a long period of time, the body tries to remove it by increasing the amount excreted in the urine.
Thus, if you take multiple large doses throughout the day say, every two hours , most will be either unabsorbed or quickly excreted. For adults, the recommended daily amount for vitamin C is 65 to 90 milligrams mg a day, and the upper limit is 2, mg a day. Although too much dietary vitamin C is unlikely to be harmful, megadoses of vitamin C supplements might cause: Diarrhea. Improve this question. Physiks lover Physiks lover 1 1 gold badge 3 3 silver badges 10 10 bronze badges.
Add a comment. Active Oldest Votes. Improve this answer. Laura Laura 5, 7 7 gold badges 33 33 silver badges 65 65 bronze badges. Andrews' answer for explanations. Actually, vitamin C degrades with heat.
The following, by dietician Jill Irvin, says it all: Vitamin C is one of the least stable of all vitamins in solution and is oxidized readily in light, air and when heated. Marti 4, 5 5 gold badges 35 35 silver badges 47 47 bronze badges. David N. This is the only answer that "answers" the OP's question.
Vitamin C gets degraded with temperature. Or the reason you don't find traces of it in baked bread, despite they add E to enhance the dough. From ncbi. When people boil vegetables , the vitamin C is dissolved in water; that is what soluble in water means. Or mash potatoes with some of the potato water. Also, cast iron pans destroy vitamin C. Vitamin C can be completely lost if foods are frozen for longer than two months. Keep your freezer at 0 to degrees to minimize this vitamin C loss in juices and vegetables.
Orange juice is frequently bought as a frozen concentrate. Fat-soluble nutrients such as vitamins A, E and K are more stable and fare better during cooking. So do carotenoids e. Water is the enemy when it comes to nutrient losses during cooking. That's why steaming is one of the best methods to preserve easily damaged nutrients, such as vitamin C and many B vitamins.
Since vegetables don't come in contact with cooking water during steaming, more vitamins are retained. Dry cooking methods such as grilling, roasting and stir-frying also retain a greater amount of nutrients than boiling. If you prefer to boil your vegetables, save the nutrient-rich cooking water to add to soups and sauces. Contrary to popular belief, microwaving does not kill nutrients in vegetables. In fact, it may outrank steaming when it comes to retaining antioxidants.
A report in the Journal of Food Science found that compared with boiling, pressure cooking and baking, microwave cooking helped maintain the highest levels of antioxidants in beans, beets, artichoke, asparagus, garlic, onion and spinach. Microwave cooking increased antioxidant activity in eggplant, corn, peppers and Swiss chard.
On the other hand, boiling and pressure cooking led to the greatest antioxidant losses. Cornell researchers found that spinach retained nearly all of its folate when microwaved but lost most of the B vitamin when boiled on the stove.
Microwave ovens use less heat than many other cooking methods and involve shorter cooking times. If you use a minimal amount of water and don't overcook your vegetables, microwave cooking is a nutritional win.
A study concluded that microwaving destroyed most of the antioxidants in broccoli — but the researchers had added far too much water. Many people think raw vegetables are more nutritious than cooked, but that's not the case. Cooking vegetables breaks down the plants' cell walls, releasing more of the nutrients bound to those cell walls.
Cooked vegetables supply more antioxidants, including beta-carotene, lutein and lycopene, than they do when raw. Cooked vegetables also deliver more minerals. Spinach, beet greens and Swiss chard are high in calcium, but a compound called oxalic acid binds with calcium. Heating releases bound calcium, making more of the mineral available for the body to absorb.
Cooking vegetables also increases the amount of magnesium and iron that are available to the body. Even so, in some cases vegetables may be better for you raw than cooked. Cruciferous vegetables — cabbage, cauliflower, broccoli, bok choy, Brussels sprouts — contain an enzyme called myrosinase, which, when you chop or chew these vegetables, converts glucosinolates phytochemicals to anti-cancer compounds called isothiocyanates.
The problem: Myrosinase is easily destroyed by heat. Cooking cruciferous vegetables reduces the conversion of glucosinolates to their active isothiocyanates, which may reduce their cancer-fighting potential. According to research published in , steaming led to the lowest loss of glucosinolates in broccoli while stir-frying and boiling both higher-heat cooking methods caused the greatest loss. Cooking isn't the only way vegetables can lose nutrients. Before fresh vegetables reach your steamer basket or microwave, some of their nutritional value can be degraded during the time they're transported to a distribution centre, displayed in the grocery store and stored in your crisper.
When possible, buy produce from farmers' markets to reduce the time from harvest to table. Frozen vegetables closely match the nutrient content of their freshly picked counterparts because they're flash-frozen at peak ripeness, a time when they're most nutrient-packed. Vegetables that are shipped to the produce section of grocery stores are usually picked before they are ripe, giving them less time to develop their full nutritional potential.
No one cooking method will preserve per cent of the nutrients and protective phytochemicals in vegetables. Eat your vegetables roasted, grilled, steamed, boiled in a soup, microwaved and raw. Enjoy them fresh locally grown when possible and frozen. The more variety you have, the more likely you are to eat them. And that's the whole point. Leslie Beck is a registered dietitian in Toronto.
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Leslie Beck is a contributing writer for The Globe and Mail. She continues to help thousands of individuals achieve their nutrition and health goals. Her integrative approach offers clients dietary advice, personalized meal plans and science-based recommendations on the use of nutritional supplements. Leslie is recognized by the media as an authority on nutrition and food issues and is an experienced communicator in television, radio and print media.
Her books are published by Penguin Group Canada.
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