Although vegetables contain starch, sugar and protein, their main sources are vitamins, minerals, fiber and protective phytochemicals. Their nutrient content, color and texture depend on the method of preparation, the cooking time and the volume of water used. Here are some tips on the right ways to conserve nutrients in vegetables.
- The yellow carotene pigments are not soluble in water and are well preserved during cooking, but the vitamin C and the B vitamins penetrate in the cooking liquid.
- Vitamin C is also destroyed when in contact with oxygen. Additionally, up to 20% of a vegetable’s vitamin C can be lost every minute when switching from cold water to a boil. Indeed, an enzyme which destroys vitamin C becomes more active when the temperature increases; however, the destruction of vitamin C stops at the time of boiling.
- Vegetables should be added to boiling water.
- Steaming or cooking in a small amount of water stores twice as much vitamin C as in boiling water.
- Some cooks blanch vegetables such as beans and broccoli in boiling water for a minute or two, then dip them in cold water to retain the color. This is fine for vegetables that are served cold, but if they are served hot, they must be reheated quickly or more nutrients may be lost.
- In order to preserve the betacyanin contained in beets, avoid heating them in boiling water. It is best to roast, bake or microwave whole beets with their skins on. Peeled or cut beets penetrate the pigments of the vegetable, causing loss of betacyanin. In addition, cooking in boiling water decreases the folate in beets, which is soluble in water.
Since harvested vegetables lose their flavor, sweetness and texture when using their own food resources, it is best to keep them as short as possible.
- Corn and peas can lose up to 40% of their sugar if stored at room temperature for just six hours after picking.
- Beans and stem vegetables, such as broccoli and asparagus, usually harden.
- Vegetables that come from hot climates (especially beans, eggplants, peppers, okra, squash, and tomatoes) store best at 10 ° C (50 ° F).
- Potatoes convert their starch into sugar at temperatures below 4 ° C (40 ° F); keep them cool and protected from light to prevent the formation of toxic alkaloids.
- Most other vegetables store best at 0 ° C (32 ° F). The salts and sugars in their sap prevent them from freezing except when exposed to lower temperatures.
- Tomatoes should not be placed in the refrigerator: the cold destroys the flavor. They keep best on the kitchen counter and are better to consume quickly.
- Potatoes, squash and sweet potatoes store best in a cool, dark place, not in the refrigerator.
- Green vegetables should be washed, drained, wrapped in paper or cloth napkins and stored in an airtight container in the refrigerator. If you bought them in an airtight package, keep them as is.
- The peppers should be put in the refrigerator, away from the fruit.
Most vegetables are good to eat raw or cooked.
- Lima beans and kidney beans as well as other legumes contain toxic substances that disappear when cooked.
- Broccoli, kale, and other cruciferous vegetables contain goitrogenic compounds that can interfere with iodine metabolism. Cooking deactivates these compounds, but if you eat large amounts of these raw vegetables, it can worsen an already existing thyroid problem.
- Most vegetables don’t cause allergies, but some people react to members of the nightshade family, which includes eggplants and tomatoes. Corn is another common allergen.