Conserving the Nutritive Values in Foods 1983 -- Consumer Nutrition Division Human Nutrition...|
Conserving the Nutritive Values in Foods |
Consumer Nutrition Division
Human Nutrition Information Service
Home and Garden Bulletin 90, USDA, 1963.
Slightly revised April 1983
Archive copy of publication, do not use for current recommendations.
The PDF file was provided courtesy of the National Agricultural Library.
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5 Holding and reheating
6 Fruits and fruit juices
6 Canned foods
7 Effects of storage
7 Nutrients in liquids
7 Frozen foods
8 Meat, poultry, and fish
8 Nutrients in drippings
8 Cooking losses
10 Whole grain, enriched or restored
10 Cooking losses
Consumer Nutrition Division,
Human Nutrition Information Service
Issued August 1963
Slightly revised November 1977
Slightly revised April 1983
Nutritive Values in
The great variety of foods
available today makes it possible for
homemakers to select foods that
provide the vitamins, minerals,
protein, and other food nutrients
needed for the good health of their
This bulletin calls attention to
some of the important nutrients in
foods that are affected by different
practices of handling and preparation
and suggests ways in which these
nutrients can best be conserved in the
Such information affords
guidelines for meal planning and
preparation that will assure overall
adequacy of the diet while allowing
for individual preferences in the
selection of foods and the form in
which they are served.
Foods differ in their content of
the nutrients known to be essential in
nutrition. Some foods are very rich
sources of one nutrient, and supply
only small amounts of others; some
foods are valuable sources of many
Nutrients in foods vary greatly in
their stability. Some nutrients, such as
carbohydrate, are not affected to any
great extent by ordinary handling.
Other nutrients, such as vitamin C
(ascorbic acid), are readily lost from
some foods, although stable in
others. Vitamin C is soluble in water;
air and heat hasten its loss.
Because vitamin C is more easily
destroyed than other food values,
conservation of vitamin C is often
used as an index to the retention of
other nutrients. Measures that protect
vitamin C usually protect other
nutrients. Many improvements in
ways of handling and processing
fruits and vegetables have resulted
from vitamin C research.
Fortunately some of the most
important sources of vitamin C—
citrus fruits and tomatoes—retain this
nutrient very well.
Vegetables—fresh, frozen or
canned—provide a year-round
source of vitamins C and A. They also
provide several valuable minerals,
particularly calcium and iron. To
conserve food values and flavor,
trim, store, and cook vegetables
Fresh vegetables usually need
some trimming, peeling, or scraping
before they are cooked or served to
remove damaged leaves, bruised
spots, skins and inedible parts.
Different parts of the plant differ
in nutrient content. For example, the
leafy parts of collard greens, turnip
greens, and kale have much more
vitamin A value than the stems or
midribs. If the fibrous stems and
midribs are removed, little loss of
nutrients occurs. Such trimming is
worthwhile if it makes the nutritious
parts of these vegetables more
acceptable to the family.
Outer green leaves of lettuce are
coarser than the inner, tender leaves,
but have higher calcium, iron, and
vitamin A value. Use the outer leaves
In trimming cabbage, keep in
mind that the core, as well as the
leaves, is high in vitamin C.
Broccoli leaves have much
higher vitamin A value than the stalks
or flower buds. If broccoli leaves are
tender when you get them home,
plan to eat them; keep them cool and
moist until you can use them.
Losses of vitamins A and C occur
when vegetable tissues are bruised.
To prevent bruising use a sharp blade
when trimming, cutting, or shredding
Proper storage of fresh
vegetables helps conserve their
original food values. The length of
time raw vegetables are stored, as
well as storage temperature and
humidity, affects retention of their
Vegetables such as kale,
spinach, broccoli, turnip greens,
chard, and salad greens need to be
refrigerated promptly in the vegetable
crisper or in moisture-proof bags.
They keep their nutrients best at near-
freezing temperature and at high
Cabbage—a more stable source
of vitamin C than most leafy
vegetables—should not be allowed to
dry out. If it is to be held at home for
a few days, it should be wrapped or
put in the vegetable crisper of the
refrigerator, where the humidity is
high. Stored in this way, cabbage
holds its vitamin C well.
Green peas and green lima
beans hold their nutrients better if left
in their pods until ready to use. If
shelled, put them into plastic bags
before storing in the refrigerator.
Tomatoes bought or picked
before they turn red keep their
nutrients best if they are ripened out
of the sun at temperatures from 60°
to 75° F. Cover under-ripe tomatoes
with a cloth and leave them at room
temperature. Do not ripen tomatoes
on a hot window sill or in the
refrigerator. The bright-red color does
not develop when the (ripening)
temperature goes above 85° for very
long. Tomatoes become soft and
watery and subject to decay if
ripened in the refrigerator.
Ripe, firm tomatoes, held in the
refrigerator or at a cool room
temperature for several days, do not
lose much vitamin C. When they
become overripe, the loss of vitamin
C is increased.
potatoes, and other roots and tubers
retain their most important food
values reasonably well if they are
kept cool and moist enough to
Methods—One of the best
methods of cooking vegetables to
conserve maximum food values is to
cook them only until tender in just
enough water to prevent scorching.
Use a pan with a tight-fitting lid.
Covering the pan helps prevent the
escape of steam and vapor so that
vegetables can be cooked quickly in
a small amount of water.
The amount of water used in
cooking vegetables is of major
importance in preventing loss of
water-soluble nutrients, such as
vitamin C, the B vitamins, and some
of the minerals. The smaller the
amount of water used in cooking, the
more food value retained in the
If the amount of water used in
cooking cabbage equals about one-
third the amount of cabbage, 90
percent of the vitamin C will be
retained. If a larger amount of water
is used—for instance, four times as
much water as cabbage—the
retention of vitamin C drops to less
than 50 percent.
So-called "waterless" cooking
refers to cooking vegetables with only
the water that remains on the
vegetables after rinsing and the juice
extracted from the vegetables. This
method does not permit quick
cooking, however, and conserves
nutritive values no better than
cooking vegetables quickly in a small
amount of water.
Boiling root and tuber vegetables
(carrots, sweetpotatoes, potatoes) in
their skins retains more vitamins and
minerals than cooking these
vegetables pared and cut.
Tests show that potatoes boiled
whole in their skins retain practically
all of their vitamin C, thiamin, and
Baking potatoes and sweet-
potatoes whole in their skins also
conserves the nutritive values of
these vegetables well.
Stir-frying is a quick way of
cooking vegetables in a frying pan
with a small amount of fat or oil. This
is a good method for conserving the
nutrients in succulent vegetables,
such as cabbage, summer squash,
kale, and collards.
Steaming under pressure in a
pressure saucepan is a quick and
satisfactory method of vegetable
cookery—particularly for potatoes,
turnips, and carrots—if the cooking
period is carefully timed. This is also A
practical way to cook the dry
legumes, such as dry peas, beans,
and lima beans. Prolonged cooking
under pressure often results in loss of
ment is not essential for cooking
vegetables or other foods to conserve
their nutrients. A utensil that has a lid
that fits tightly and is heavy enough to
prevent the escape of vapor and
steam is suitable for cooking with a
minimum amount of added water.
The kind of material (aluminum,
enamel, glass, stainless steel) of
which modern cooking utensils are
made is not important in conserving
the nutritive values of the foods
cooked in them. In the old-style
copper utensil, the copper was in
direct contact with food and
hastened the oxidation of vitamin C.
This, however, does not apply to
modern pans with copper-plated
bottoms because the inside cooking
surface is made of another metal.
Holding and Reheating
To save time you may like to
cook enough food for later meals, but
this saving is at the expense of
nutrients. Holding and reheating
cooked vegetables cause additional
losses of nutrients, particularly of
Vitamin C losses in cooked
vegetables increase with the length of
time they are held. They have about
three-fourths as much vitamin C after
1 day in the refrigerator as when
freshly cooked; about two-thirds as
much after 2 days.
Cooked vegetables reheated
after 2 or 3 days in the refrigerator
can be depended on for only one-
third to one-half as much vitamin C
as when freshly prepared.
These losses need not cause
concern if your meals include other,
more dependable sources of vitamin
C each day.
Fruits and Fruit juices
Many kinds of fruit once
considered luxuries now are eaten
regularly. Some are mainstay sources
of vitamin C and a few are good
sources of vitamin A value. Fruits,
and the juices made from them, also
supply small amounts of other
vitamins, and some calcium and iron.
Fruits are low in sodium, which
makes them especially desirable for
persons on low-sodium diets.
Vitamin A value varies from fruit
to fruit. Fruits high in vitamin A value
include apricots, yellow-fleshed
peaches, cantaloups of the deeply
colored varieties, mangoes, and
Of the commonly used fruits and
fruit juices, those of the citrus
family—oranges, grapefruit, lemons,
limes, and tangerines—are highest in
vitamin C. Guava, a popular fruit in
Hawaii, is also a rich source of
Fortunately vitamin C is well
retained in citrus fruits and juices.
Citrus fruits and their juices are
canned or frozen with very little loss
of vitamin C.
Whole citrus fruits keep their
nutrients well several days at room
temperature or slightly cooler (60° to
Fresh oranges lose edible
material—and therefore nutritive
value—when they are squeezed and
the juice strained. The edible yield of
an orange as strained juice is only
about two-thirds to three-fourths that
of the orange eaten by sections.
Orange juice, whether freshly
squeezed, canned, or reconstituted
from frozen concentrate, can be held
in the refrigerator for several days
before any vitamin C is lost. A few
hours outside the refrigerator does
not cause any serious loss in vitamin
C, although it may impair flavor.
Orange juice changes in flavor before
much of its vitamin C is lost.
For practical purposes, foods
stored in the refrigerator are usually
covered, but a lid on the orange juice
container makes no important
difference in retaining vitamin C.
There is no harm in keeping fruit
juices in the can.
Unlike citrus fruits, berries are
highly perishable and need careful
handling to conserve their nutrients.
They lose vitamin C quickly if capped
Strawberries compare favorably
with citrus fruits in vitamin C. About a
cup of ripe strawberries fills an adult's
daily need for vitamin C.
Canning, one of the most
familiar forms of food preservation,
has made an important contribution
to the variety, quality, and safety of
our food supply. Some loss of
vitamins in the canning process is to
be expected. Losses, however, have
been reduced considerably by
improved processing techniques.
Keeping canned foods in a cool,
dry place and limiting the length of
time they are in storage are essential
factors in conserving the nutrients in
canned foods. In general, the longer
the storage period and the higher the
storage temperature, the greater the
loss of nutrients.
Effects of Storage
Canned Fruits and Vegetables—
Vitamins are retained best when
canned foods are kept in a cool
place. Only small losses of vitamin C,
about 10 percent, occur when these
foods are stored for a year at 65° F.
When the temperature is 80°, losses
may reach 25 percent in a year.
Canned citrus juices hold
vitamin C especially well.
Carotene, a precursor of vitamin
A, is well retained in canned fruits
and vegetables. Losses average only
about 10 percent in a year when cans
are stored at 80° F. Canned tomato
juice, a particularly stable, year-
round source of carotene, shows no
loss of this nutrient.
Thiamin in canned fruits and
vegetables is well retained when
stored for 1 year at 65° F. When
stored at 80° for 1 year, losses may
increase to 15 percent in canned
fruits, and to 25 percent in canned
thiamin is lost from canned meats in
storage. Pork luncheon meat, for
example, may lose about 20 percent
of its thiamin by the end of 3 months
and 30 percent by the end of 6
months when it is stored at 70° F.
Losses accelerate at higher
Riboflavin, another B vitamin
supplied by meat, is not affected by
ordinary storage temperatures.
Nutrients in Liquids
To get the full nutritive value
from canned vegetables, serve any
liquid in the can or jar along with the
vegetables or make use of the liquid
in some other way, such as in gravy
or adding it to soup.
Usually the drained solids in
canned vegetables make up about
two-thirds of the total contents of the
cans. Soon after canning, the water-
soluble nutrients in the vegetable
distribute themselves evenly
throughout the solids and the liquid.
The solids thus contain about two-
thirds of the soluble nutrients, and the
other third is in the liquid.
Freezing offers a good way of
retaining the nutrients and the eating
quality of food. There is little loss of
vitamin C in freezing fruits. Some
fruits, such as peaches and mixed
fruits, have vitamin C added in the
freezing process. In vegetables the
amount of vitamin C is reduced
during the blanching process before
freezing. There is also a small loss of
other water-soluble vitamins and
some minerals when the blanching is
done in water.
When properly packaged, frozen
meat, poultry, and fish compare
favorably with fresh products in food
An essential requirement in
maintaining the food value and
quality of home-frozen or purchased
frozen foods is a storage temperature
of 0° F or lower.
If your home freezer or the
freezing compartment of your
refrigerator cannot be maintained at
0° F or lower, it is important to
realize that food stored will not hold
its best nutritive value and highest
quality. It may be desirable to buy
frozen foods in small quantities and
replenish your supply frequently.
Storage of frozen foods at too
high a temperature hastens vitamin C
loss. The loss increases with time.
Even at 0° F, some losses occur.
Stored at 0° for a year, frozen beans,
broccoli, cauliflower, and spinach
would lose from one-third to three-
fourths of their vitamin C. At higher
temperatures, the losses would be
Frozen concentrated orange
juice, however, holds its vitamin C
content remarkably well even at
freezing temperature (32° F).
Thawing and refreezing of
frozen foods should be avoided
because of the adverse effect on
nutrient content and flavor and the
possibility of spoilage.
Meat, Poultry, and Fish
Meat, poultry, and fish are
normally the most expensive foods
on your grocery list. They are the
main dishes about which most
homemakers plan their meals.
From this food group come
protein of high quality, fat, minerals,
and valuable vitamins.
Liver, in particular, is rich in
many nutrients. It contains protein, B
vitamins, and minerals; it is an
excellent source of vitamin A, and
also provides some vitamin C.
Among the meats, pork is an
exceptionally good source of thiamin.
The price paid per pound of
meat is not necessarily a measure of
its nutritive value. The cheaper cuts
and grades of lean meat can be just
as full of food value as the higher-
priced steaks and chops. The protein
in one is just as valuable as in the
other. The main difference is that
cheaper cuts require greater skill in
cooking and seasoning.
Nutrients in Drippings
To get the full nutritive value
from any meat, you should conserve
the water-soluble B vitamins.
Meat drippings contain some of
these B vitamins. Included are the
drippings from thawing frozen meat,
the drippings from cooking meat, and
the juices released in slicing meat.
When meats and poultry are
stewed, some of the B vitamins
transfer into the meat stock or broth.
Meat stock or broth can be used in
nourishing soups or used as a part of
the liquid in escalloped or creamed
After broiling, frying, and
roasting meats and poultry, you may
wish to skim off fat that rises to the
top of pan drippings and use the
remaining drippings in savory gravies
or pour them directly over the meat
when it is served. In this way, you
recover some of the water-soluble B
vitamins and extend the flavor of the
Meats shrink in weight and
volume as they cook. Much of the
change is water, which evaporates or
goes into the drippings. Some fat also
is in the drippings.
The protein value of meat is not
destroyed by cooking, and only small
amounts of it go into the drippings.
Even when meats and poultry
are stewed in large amounts of water,
not more than 10 percent of the
protein passes from meat to broth.
Some thiamin and vitamin Be are
lost in cooking; riboflavin and niacin
are less susceptible to loss in cooking.
Roasting beef to the rare stage
conserves more thiamin than cooking
it to the well-done stage.
To best conserve the valuable
nutrients and good flavor of milk,
keep it cold, covered, and away from
Milk is one of the best sources of
calcium and the B vitamin, riboflavin.
The protein it supplies rates high.
Dietary studies in the United States
indicate that milk and milk products
provide about two-thirds of the total
calcium, nearly half of the riboflavin,
and more than a fifth of the protein in
Calcium, protein, and vitamin A
are stable and well retained in milk.
The total loss of riboflavin in milk
from the time of production until it is
served can be kept low with proper
Milk has about the same calcium
and protein value whether you drink
it as whole, skim, or reconstituted
from nonfat dry milk or evaporated
Whole milk and cream are
reliable sources of vitamin A. Skim
milk, fresh or powdered, has nearly
all the fat removed from it, and has
little vitamin A value unless it is
fortified. A glass of fresh skim milk or
reconstituted nonfat dry milk has only
about half the calories of a glass of
Cottage cheese is made from
skim milk and has a lower calorie
value than cheeses made from whole
milk. Cheeses made from cream or
whole milk have a much higher
content of fat and vitamin A than
cheese made from skim milk.
Pasteurization of raw milk, a
necessary health safeguard, does not
destroy the principal nutrients in milk
and milk products—the calcium,
protein, riboflavin, and vitamin A.
Riboflavin, an important nutrient
in milk, is subject to reduction by
exposure to direct sunlight, daylight,
or artificial light. However, it is well
protected by present methods of
handling milk from the farm to the
Eggs have an established place in
family meals—both by themselves
and in cooked products. Like meat
and milk, eggs supply high-quality
protein. Two eggs have about as
much protein as 2 ounces of cooked
hamburger. One large egg furnishes
about 80 calories.
Egg yolk is a rich source of iron,
a mineral important in building red
blood cells. Eggs also supply vitamin
A and riboflavin.
When properly stored and
cooked, both shell eggs and dried egg
retain most of their nutrients well.
Shell eggs keep in the refrigerator
or in cold storage without serious loss
of nutritive value.
Cooking losses in eggs are not
high, probably because the cooking
period is short and the temperatures
fairly low. The protein and vitamin A
values are well retained. Riboflavin is
well retained when eggs are cooked
in the shell, but small losses may
occur with other methods of
cookery. Thiamin losses are small
also, usually not more than 15
When dried egg is properly
stored (tightly covered in the
refrigerator), it has practically the
same nutritive value as shell eggs.
Dehydration does not reduce the
protein, vitamin A, or riboflavin
Stored at ordinary room
temperatures, dried egg loses about a
third of its vitamin A value in 6
months, and about two-thirds in 9
months. The rate of loss accelerates
at higher temperatures.
The cereals—wheat, corn, rye,
rice, and oats—come to your table in
a myriad of food items, including
breakfast foods, hominy, breads of all
kinds, macaroni and noodle
products, puddings, pastries, cakes,
Cereals are nutritional bargains.
They are economical sources of food
energy, protein, minerals, and the B
The amount of vitamins and
minerals your family gets from a
cereal or a cereal product depends
on how much remains after milling,
what nutrients are added, and on
how you prepare it for eating.
Whole Grain, Enriched or Restored
Whole-grain forms of cereals
retain the germ and outer layers of
the grain where the B vitamins and
minerals are concentrated.
Whole-grain products generally
available on the market include:
Whole-wheat flour, sometimes called
graham flour; brown rice, dark rye
flour, whole-ground cornmeal, and
rolled oats or oatmeal, and bread and
other products made from them.
Milling whole cereal grains into
refined products removes all or part
of the germ and a considerable
amount of the outer layers.
Most consumers prefer white
bread and other products made of
refined cereal grains. Some of the
milling losses are offset through
enrichment of certain staple cereal
Enriched cereals are milled
cereals to which the B vitamins—
thiamin, riboflavin, and niacin—and
iron have been added within the
limits specified by the Federal
standards of enrichment. Provision is
made for the optional addition of one
other nutrient, calcium.
Federal standards for enrichment
have been established for certain
wheat flours, bread, rolls and buns,
farina, cornmeal, corn grits, macaroni
and noodle products, and rice.
Enriched flour has about ten
times as much thiamin, eight times as
much riboflavin, six times as much
niacin, and about four times as much
iron as unenriched flour.
Many manufacturers of breakfast
cereals add nutrients to their
products. The amounts and kinds of
nutrients added vary widely since
there are no Federal standards for the
addition of nutrients to these
A comparison of the nutritive
values of different forms of rice
shows that parboiled rice is
intermediate in food value between
highly-milled, polished rice and
brown rice. Brown rice is the
unprocessed kernel with the hull
removed; from a nutritional
standpoint, it is considered a whole
Cooking cereals in excessive
quantities of water, draining off the
cooking water, and rinsing afterward
Some persons persist in washing
rice before cooking. This is an
unnecessary step because today's
packaged rice has already been
cleaned. Moreover, washing is
nutritionally expensive. Washing rice
once before cooking can cause a
thiamin loss of 25 percent in regular
white rice, and a loss of 10 percent in
brown or parboiled rice. This loss
may be important in diets of persons
who eat a great deal of rice.
You may have noticed these
directions on some rice packages:
"To retain vitamins, do not rinse
before or drain after cooking."
The nutrients in rice are well
retained if rice is cooked in just
enough water to be absorbed during
the cooking period.
Cooking causes little loss of
nutrients from ready-to-cook
breakfast foods, such as rolled oats,
rolled wheat, hominy grits, cracked
wheat, farina, and others. Many of
the breakfast cereals on the market
are precooked and require only
seconds to prepare.
Baking, one of the popular ways
of cooking cereal products, permits
good retention of thiamin. You can
conserve thiamin by—
• Baking the product only until
the crust is light brown.
• Limiting the surface area
exposed to heat. For example, less
thiamin is lost when cornbread batter
is baked in a pan rather than as sticks.
Toasting causes additional loss of
thiamin. However, the thicker the
slice of bread and the lighter the
finished product, the smaller is the
loss of thiamin.
One comparison showed a
toasting loss to be only half as great in
a thick slice as in a thin slice.
Riboflavin, another B vitamin in
cereals, is not greatly affected by heat
but is sensitive to light. Experimental
studies of riboflavin loss in
commercially baked bread indicate
that heavy wax paper or other
translucent covering protects the
riboflavin in bread very well.
Be Vitamin-Wise When You
• In general, freshly harvested
vegetables have more vitamins than
those held in storage.
• Make full use of vine-ripened
tomatoes in summer when they are
plentiful and inexpensive. Tomatoes
vine ripened out-of-doors in summer
sunlight have twice as much vitamin
C as tomatoes grown in greenhouses
• You get several times as much
vitamin A value from bright-orange,
mature carrots as from pale-colored,
young ones. Even so, young carrots
are a good source of vitamin A;
choose them if you prefer.
• Choose deep-orange
sweetpotatoes for maximum vitamin
• Among the vegetables, turnip
greens, kale, and collards are good
sources of riboflavin as well as of
vitamins A and C. Lima beans, peas,
and young cowpeas, including black-
eye peas, contribute appreciable
amounts of thiamin and protein.
• Peppers are high in vitamins A
• The dark-green leafy
vegetables are richer in nutrients,
particularly vitamin A, calcium, and
iron, than light-green vegetables.
• Leaf lettuce has more vitamin
A value than pale-green head lettuce.
The dark-green, outer leaves of head
lettuce are much higher in vitamin A
value than the inner leaves. For
maximum food value, look for dark-
• Potatoes, although not rich in
vitamin C, are a good source of this
nutrient when eaten regularly.
• If the tops of beets are
attached and still tender when you
buy them, cook them—they are rich
in vitamin A value.
U.S. GOVERNMENT PRINTING OFKCCE : 1983 0 - 389-992