Vitamins that Nature put into her produce as it ripened on the vine (or on the hoof) do us no good if we somehow lose or inactivate them before they reach the dinner table. How food is handled can make a big difference in its nutritional value. Without becoming obsessed with the subject, one can still observe a few reasonable precautions in the kitchen.

1. Store foods in a cool dark place, and for as short a time as possible. As soon as foods leave the farm, vitamins start to leave the foods. The best approach, if you can manage it, is to sprint with an armload from the cabbage patch to the kitchen, where the water is already boiling on the stove. Foods are not only more nutritious this way, but more delicious too. For those of us who find this technique impractical, the second best approach is to store foods wisely. Don't buy fresh vegetables you won't be using up soon; as they sit in the refrigerator, enzymes within their cells inactivate many of their important vitamins. Keeping them cold and dark slows down these enzymatic reactions. Darkness is especially important for storing milk, which can lose 10 percent of its riboflavin each hour when exposed to sunlight. (This is less of a problem now than it was in the old days when milk was delivered onto doorsteps in glass bottles.)
         Vegetables that have been frozen or canned lose their vitamins less rapidly during storage than fresh ones do because the heat used in commercial processing destroys the vitamin-inactivating enzymes. Still, frozen and canned fruits and vegetables do become less vitamin-rich over a period of months, and these processed foods should also be kept at optimally cold temperatures if possible: -5 F for frozen foods and 45 F for canned. If your facilities aren't this cool (most people's are not), don't stock up too far ahead.

2. As much as you can, avoid bruising, cutting, mashing, pureeing, and chopping fruits and vegetables. There are three reasons for this rule: (1) Damaged plant cells release vitamin-destroying enzymes. (2) Air inactivates some vitamins, and the more surface area you expose to the air, the more you lose (dehydrated potato flakes, for example, have lost all of their vitamin C). (3) Water-soluble vitamins will leach out into the cooking water faster from small pieces of food than from large ones.
         If your recipe calls for shredded or grated foods, don't fret too much about it; just do the deed right before you cook or serve the food, to minimize nutritional damage. Along similar lines, it's sensible to tear up salad greens rather than cutting them, because leaves tear around the margins of cells, releasing smaller quantities of the vitamin-inactivating enzymes.

3. Eat peelings. Because the most vitamin-rich portions of vegetables and fruits are commonly found in the skin or just beneath it, it doesn't make sense to peel these foods. (Exception: you faint-hearted are allowed to peel your grapefruit and coconuts.) Potatoes, for example, can be mashed or french-fried peeling and all, and they are quite tasty that way.
 
4. Cook in small quantities of water, and save the "pot liquor". The most important cause of nutrient depletion during food preparation is the loss of water-soluble vitamins discarded with cooking liquids. Vitamin C and all the B-vitamins (especially thiamin) go down the drain by tank loads this way.
         The difference in vitamin C content that these vegetables bring to the dinner table is certainly dramatic. But water-soluble vitamins can be reclaimed by using the vegetables cooking water ("pot liquor") in other dishes, such as breads, soups, and stews. Meats, too, lose some water-soluble B-vitamins during cooking if the cook throws away the pan juices. Making gravy from the drippings salvages the important B-vitamin thiamin, but you should he sure to let the meat juices stand long enough to allow skimming off the fat before you thicken the gravy; otherwise, the vitamin advantage will be offset by the nutritional debit of a load of saturated fat.

5. Don't overcook. High temperatures and prolonged heating progressively inactivate vitamins A and C and several B-vitamins. Even keeping cooked foods warm can be a vitamin-killer: foods held at serving temperature have been found to lose 25 percent of their vitamin C content in 15 minutes, and 90 percent of it in only an hour!

6. Don't add baking soda to green vegetables or dried beans. Some cooks do this to brighten the color of vegetables or tenderize dried beans. It works, but it also changes the acid-base makeup of the food, inactivating the B-vitamin thiamin.