Fresh, Frozen, or Canned? Raw or Cooked?
Selecting and Preparing Foods to Maximize Vitamin Content
A food’s vitamin content depends first on the original amount in the plant or animal while it is alive and growing. Although grazing materials and feed may have a minor impact on vitamin content, animal products tend to have fairly consistent levels. This reflects the animal’s ability to concentrate and store vitamins. The vitamin content of plants, however, depends more on soil and growing conditions such as
available moisture and sunlight. The maturity of a fruit or vegetable at the time it is harvested also
influences its vitamin content.
Light, heat, air, acid, alkali, and cooking fluids can attack vitamins, so proper storage, processing, and cooking are important. Ideally, you should shop for produce as the Europeans do: choose fresh fruits and vegetables daily to minimize nutrient losses associated with prolonged storage. Barring that, choose clean, undamaged produce at each of your regular shopping trips. When storing foods, avoid temperature extremes, and minimize exposure to light and air with refrigeration or covered storage. It’s best to eat fruits and vegetables soon after purchase; normal storage can decrease their vitamin content.
The vitamin C content of fresh green beans, for example, drops by half after six days at home.
What about frozen and canned foods?
The heat processing used in canning fruits and vegetables does deplete small amounts of vitamins but they end up in the liquid in which the food is packed. In addition, the vitamin content of canned foods is shelf stable and remains constant even after two years. The thiamin content of canned meats and beans is comparable to home‐prepared versions. Vegetable sources of folate, such as spinach, retain most of their folate content when canned or frozen. The carotenes in vegetables and fruits are stable during the canning process. In fact, current research suggests the lycopene in tomatoes is a more effective antioxidant (it has been linked to reducing prostate cancer)(1) after tomatoes have been heated or canned (2.) Ready‐to‐drink orange juice loses about 2 percent of its vitamin C content each day once opened (3.)
Once fruits and vegetables are home and stored carefully, what is the best way to cook them? To
maximize the vitamin content, think minimal—minimal amounts of heat, minimal amounts of cooking
water, and minimal exposure to air. Try to minimize handling the food before and during cooking.
Although dicing a food such as a potato reduces cooking time, it also exposes more surface area to
vitamin‐destroying influences. So, cut if you must, but not too small.
Steaming and microwaving are the best cooking methods for preserving vitamin content, because they minimize cooking time and water use. If you boil foods, try to use the cooking water for sauces, stews, or soups, because it contains many of the water‐soluble vitamins lost from the food during cooking. To retain the most vitamins in your food, be gentle with storage and handling, and kind with cooking. Minimize (heat, water, air exposure) to maximize!
1. Rao AV, Ray MR, Rao LG. Lycopene. Adv Food Nutr Res. 2006;51:99–164.
3. Johnston CS, Bowling DL. Stability of ascorbic acid in commercially available orange juice. J Am Diet Assoc. 2002;102:525–529.