When it comes to selecting the best, most nutritious produce, your eyes and hands are still your best guides. Crisp, dark-colored greens and brightly colored, firm fruit and vegetables with no blemishes typically contain the highest amount of nutrients.
But although a vegetable’s appearance and heft provide a good indication of whether it has been stored properly, how long can you count on those nutrients lasting?
“Each fruit and vegetable is different, so it’s hard to state generalities,” says Barbara Klein, a professor of foods and nutrition at the University of Illinois at Urbana-Champaign. But because nutrient loss begins as soon as the fruit or vegetable is picked, it stands to reason that the sooner you use it, the more nutritious it will beproviding a few other conditions are met.
The answer also depends on the nutrients you’re talking about.
Water-soluble vitamins-vitamin C and some of the B vitamins such as folic acid, thiamin, niacin and riboflavin-are abundant in many fruits and vegetables; they are easily destroyed by exposure to air, light, heat and water.
But fat-soluble carotenoids, plentiful in dark green and bright orange, red and yellow fruits and vegetables, are much more stable and show little loss during preparation and cooking.
The minerals in many fruits and vegetables, such as calcium, potassium, magnesium, selenium, iron and zinc–are unaffected by storage, preparation or cooking.
There are no hard and fast statistics on the percentage of nutrients that are lost from the time the produce is harvested to the time you buy it and actually use it.
“Most farmers pick their produce 24 to 48 hours before the market opens, which is as farm-fresh as you can get short of growing it yourself,” Klein says. “But what they do with it after harvest has a tremendous impact on nutrient quality. Some farmers properly store their goods in refrigerated trucks or coolers, but others don’t.
“When you add in the fact that many market stands are out in the hot sun for four to six hours with no shade protection for the produce, you’re looking at a potentially significant loss of nutrients.”
Assuming proper storage, produce from farm markets are fresher than those from supermarkets.
One reason for this is the lag time between harvest and arrival in the supermarket: typically 7 to 14 days, Klein says. Though this delay undoubtedly lowers nutrient content, packing and handling systems strive to minimize the loss. Refrigerated trucks and warehouses that maintain ideal humidity and temperature for their particular crops are a highly developed industry. Inside the supermarket, refrigerated cases and “modified atmosphere packaging” help prolong shelf life.
“Water misters also help retain freshness by keeping humidity high, since when moisture is lost from the produce, so are the vitamins and minerals found in the plant cells,” Klein says. She says studies at University of Illinois show vitamin C content, a water-soluble vitamin, is actually higher in misted produce compared to produce that is not sprayed.
(But too-frequent misting leads to soggy produce, which quickly spoils, according to Penn State’s College of Agricultural Science. A rule of thumb is how wet your hand gets when picking out produce: The only time your hand should have a lot of water on it is if the mister starts up.)
Once home from the market, proper storage is key.
“The primary goal is to get it to the lowest safe temperature for that particular fruit or vegetable as quickly as possible,” says Richard Gladon, a professor of horticulture at Iowa State University. “Most produce stores best at temperatures just above freezing.”
Not all produce should be refrigerated. Tomatoes do best at room temperature, while winter squash, potatoes and onions should be kept in cool, not cold, places.
Because most fruits and vegetables are 85-95 percent water, proper humidity control is important. Gladon recommends storing fruits and vegetables in a plastic bag that has holes, which allows the produce to “breathe.” Keeping produce in completely sealed bags can cause humidity to get too high. Refrigerator crisper drawers are designed to help keep humidity and temperature at proper levels. Vegetables usually need more humidity than fruits.
Preparation guidance
Preparation methods can have a big effect on nutrient quality. These tips will help keep vitamins in fruits and vegetables at their peak:
– Wash produce just before using it, not when you get home from the market.
– Quickly but thoroughly rinse fruits or vegetables under cold running water before cooking them or serving them raw. Use a soft brush to remove dirt that clings. Avoid soaking, which can leach out the water-soluble vitamins.
– Don’t use dish soap for washing fruits and vegetables, because their porous surfaces can absorb detergent. Produce cleaning sprays are fine, but experts contend that plain old running water does the trick.
– Wait to cut up vegetables and fruits until the last minute. Exposure to air can increase loss of some vitamins.
– Keep peels on if you can, because many nutrients are found just underneath. If possible, cook vegetables with the skin on and peel them afterward.
Cooking methods
The best methods-steaming, microwaving and pressure-cooking-use a minimal amount of liquid, or the liquid doesn’t touch the vegetables. Stir-frying also is good because vegetables stay in the hot pan for so short a time.
Nutritionally speaking, boiling is the worst way to cook vegetables because it causes the water-soluble vitamins to leach into the cooking liquid. If you must boil, use the least amount of water possible and cover the pot with a lid, which shortens cooking time and cuts down on the loss of vitamins. Make sure the water is boiling when the vegetables are put in the pot; most nutrients are lost during the first 2 to 3 minutes of cooking while the water is returned to a boil.
With the exception of foods like potatoes and other root vegetables, cook vegetables until they are crisp-tender or barely fork-tender. This also gives the brightest colors and freshest flavors.
STORING PRODUCE
ITEM: Apples
SHELF LIFE: 14-28 days
STORAGE TIPS: In perforated bag in crisper drawer
ITEM: Asparagus
SHELF LIFE: 2-4 days
STORAGE TIPS: Wrap stalk bottoms in damp paper towels and store in open plastic bag in crisper or stand them in a little water.
ITEM: Bananas
SHELF LIFE: 1-2 days
STORAGE TIPS: Once ripe Store at room temperature. Can refrigerate once ripe; skins will darken but bananas will keep up to 2 weeks.
ITEM: Broccoli
SHELF LIFE: 3-4 days
STORAGE TIPS: In open plastic bag in coldest part of refrigerator
ITEM: Cantaloupe
SHELF LIFE: 3-5 days
STORAGE TIPS: Ripen at room temperature then store unbagged in cold part of refrigerator.
ITEM: Cherries
SHELF LIFE: 2-4 days
STORAGE TIPS: In open or perforated bag in refrigerator
ITEM: Corn
SHELF LIFE: Eat as soon as possible.
STORAGE TIPS: In open plastic bag in coldest part of refrigerator
ITEM: Grapes
SHELF LIFE: 4-5 days
STORAGE TIPS: In open plastic bag in refrigerator
ITEM: Green beans
SHELF LIFE: 3-4 days
STORAGE TIPS: In open bag on refrigerator shelf
ITEM: Lettuce
SHELF LIFE: 5-7 days
STORAGE TIPS: In open plastic bag in crisper drawer, away from apples, oranges and melons (their gas speeds spoilage of greens)
ITEM: Mushrooms
SHELF LIFE: 2-4 days
STORAGE TIPS: Leave in original packaging or in paper bag in coldest part of refrigerator.
ITEM: Peaches
SHELF LIFE: 3-6 days
STORAGE TIPS: Ripen at room temperature, then refrigerate.
ITEM: Peppers
SHELF LIFE: 3-5 days
STORAGE TIPS: In plastic bag on cool refrigerator shelf
ITEM: Strawberries
SHELF LIFE: 3-5 days
STORAGE TIPS: In coldest part of refrigerator
ITEM: Tomatoes
SHELF LIFE: 3-5 days
STORAGE TIPS: Ripen at room temperature away from sunlight, then eat immediately; do not refrigerate whole tomatoes.
ITEM: Zucchini and other summer squash
SHELF LIFE: 4-7 days
STORAGE TIPS: In perforated bag in crisper drawer
Source: Adapted from Produce Tips: Selection, Care and Handling, 2000. Produce Marketing Association
