Foods Containing Protein, or Nitrogenous Matter.
Animal foods contain nutritive matter in a concentrated form, and
being chemically similar to the composition of the body is doubtless
the reason why they assimilate more readily than vegetable foods,
although the latter are richer in mineral matter. The most valuable
animal foods in common use are meat, eggs, milk, fish, gelatin and
fats.
MEAT.
Meat is composed of muscular tissue, connective tissue or gristle,
fatty tissue, blood-vessels, nerves, bone, etc. The value of meat as
food is due chiefly to the nitrogenous compound it contains, the most
valuable being the albuminoids: the gelatinoid of meat is easily
changed into gelatin by the action of hot water. Gelatin when combined
with the albuminoids and extractives has considerable nutritive value.
Extractives are meat bases, or rather meat which has been dissolved by
water, such as soup stock and beef tea. The object in cooking meat is
to soften and loosen the tissue, which renders it more easily
digested. Another object is to sterilize or kill any germs which may
exist and to make it more palatable. The digestibility of meat is
influenced by the age of the animal killed and the feeding. The
following table is given as an average of the digestibility of animal
foods:--
TABLE OF COMPARATIVE DIGESTIBILITY.
_Commencing with the most digestible and ending with the least
digestible of meats and other animal foods._ (Thompson.)
Oysters.
Soft cooked eggs.
Sweetbread.
Whitefish, etc.
Chicken, boiled or broiled.
Lean roast beef or beefsteak.
Eggs, scrambled, omelette.
Mutton.
Bacon.
Roast fowl, chicken, turkey, etc.
Tripe, brains, liver.
Roast lamb.
Chops, mutton or lamb.
Corn beef.
Veal.
Duck and other game.
Salmon, mackerel, herring.
Roast goose.
Lobster and crabs.
Pork.
Fish, smoked, dried, pickled.
Cooking affects the digestibility of meat, which is evident from the
figures given in the following table (Church):--
TIME OF DIGESTION.
--------------------+----------------
| Hours.
--------------------+----------------
Beef, raw | 2
Beef, half boiled | 2-1/2
Beef, well boiled | 2-3/4 to 3
Beef, half roasted | 2-3/4 to 3
Beef, well roasted | 2-1/4 to 4
Mutton, raw | 2
Mutton, boiled | 3
Mutton, roasted | 3-1/4
Veal, raw | 2-1/2
Pork, raw | 3
Pork, roasted | 5-1/4
Fowl, boiled | 4
Turkey, boiled | 2-1/2
Venison, broiled | 1-1/2
--------------------+----------------
It may be well to add here that animal food is more digestible when
cooked between 160° and 180° F. than at a higher temperature.
Cooking of Meat.
_(For more general information, see Recipes.)_
In boiling meat two principles must be considered, the softening of
the fibre and preserving of the juices. If the meat alone is to be
used it should be placed in sufficient boiling water to completely
cover, and kept at boiling point (212° F.) for at least ten minutes,
so as to harden the albumen and prevent the escape of the juices. The
temperature should then be allowed to fall to simmering point (175°
F.). If the water is kept boiling it will render the meat tough and
dry. If the juice is to be extracted and the broth used, the meat
should be placed in cold water; if bones are added they should be cut
or broken into small pieces in order that the gelatin may be
dissolved. If the water is heated gradually the soluble materials are
more easily dissolved. The albumen will rise as a scum to the top, but
should not be skimmed off, as it contains the most nutriment and will
settle to the bottom as sediment.
STEWING.
If both meat and broth are to be used the process of cooking should be
quite different. In stewing, the meat should be cut into small pieces,
put into cold water in order that the juices, flavoring material and
fibre may be dissolved. The temperature should be gradually raised to
simmering point and remain at that heat for at least three or four
hours, the vessel being kept closely covered. Cooked in this way the
broth will be rich, and the meat tender and juicy. Any suitable
flavoring may be added. This is a good method for cooking meat
containing gristle.
ROASTING AND BROILING.
When the meat alone is to be eaten, either roasting, broiling or
frying in deep fat is a more economical method, as the juices are
saved. The shrinkage in a roast of meat during cooking is chiefly due
to a loss of water. A small roast will require a hotter fire than a
larger one, in order to harden the exterior and prevent the juices
from escaping. Meat is a poor conductor of heat, consequently a large
roast exposed to this intense heat would become burned before the
interior could be heated. The large roast should be exposed to intense
heat for a few minutes, but the temperature should then be reduced,
and long steady cooking allowed.
Broiling (see broiling in previous chapter, p. 19.)
Varieties of Meat.
BEEF TONGUE.
Beef tongue is a tender form of meat, but contains too much fat to
agree well with people of delicate digestion.
VEAL.
Veal, when obtained from animals killed too young, is apt to be tough,
pale and indigestible, but good veal is considered fairly nutritious.
It contains more gelatin than beef, and in broth is considered
valuable, especially for the sick.
MUTTON.
Mutton is considered to be more digestible than beef, that is well fed
mutton from sheep at least three years old; but as it is more
difficult to obtain tender mutton than beef, the latter is more
generally preferred. Mutton broth is wholesome and valuable in
sickness.
LAMB.
Lamb, when tender and of the right age, is quite as digestible as beef
or mutton, but the flesh contains too large a proportion of fat.
[Illustration: FIG. 1.--Diagram of cuts of beef.]
[Illustration: FIG. 2.--Diagram of cuts of veal.]
[Illustration: FIG. 3.--Diagram of cuts of pork.]
[Illustration: FIG. 4.--Diagram of cuts of mutton.]
VENISON.
Venison is a tender meat with short fibres, which is very digestible
when obtained from young deer, but is considered to be rather too
stimulating. Its chemical composition is similar to lean beef.
PORK.
Pork is a tender-fibred meat, but is very indigestible owing to the
high percentage of fat, which is considerably more than the
nitrogenous material it contains. Pork ribs may have as much as 42 per
cent. of fat.
HAM AND BACON.
Ham is more digestible when well boiled and eaten cold. Bacon is more
easily digested than either ham or pork; when cut thin and cooked
quickly--until transparent and crisp--it can often be eaten by
dyspeptics, and forms an excellent food for consumptives.
FOWL.
Chicken is one of the most digestible of meats, contains considerable
phosphorus and is particularly valuable as food for invalids. Turkey
is somewhat less digestible than chicken. Ducks and geese are
difficult of digestion, unless quite young, on account of the fat they
contain.
GAME.
Game, if well cooked, is fairly digestible.
SWEETBREAD.
Sweetbread, which is thymus gland of the calf, is a delicate and
agreeable article of diet, particularly for invalids. Tripe, heart,
liver and kidneys are other forms of animal viscera used as
food--valuable chiefly as affording variety.
FISH.
The chief difference in fish is the coarseness of fibre and the
quantity of fat present. Fish which are highly flavored and fat, while
they may be nutritious, are much less easy of digestion than
flounder, sole, whitefish, and the lighter varieties. The following
fish contain the largest percentage of albuminoids:--Red snapper,
whitefish, brook trout, salmon, bluefish, shad, eels, mackerel,
halibut, haddock, lake trout, bass, cod and flounder. The old theory
that fish constituted "brain food," on account of the phosphorus it
contained, has proved to be entirely without foundation, as in reality
many fish contain less of this element than meat. The tribes which
live largely on fish are not noted for intellectuality. Fish having
white meat when broiled or boiled--not fried--are excellent food for
invalids or people of weak digestion. Fish should be well cooked.
OYSTERS.
Oysters are a nutritious food, and may be eaten either raw or cooked.
Lobsters, crabs and shrimps are called "sea scavengers," and unless
absolutely fresh are not a desirable food.
MILK.
Milk contains all the elements which are necessary to maintain life;
and constitutes a complete diet for infants. It will sustain life in
an adult for several months. Although milk furnishes a useful food, it
is not essential to a diet required for active bodily exercise. It is
seldom given to athletes while in active training. Adults who are able
to eat any kind of food are kept in better health by abstaining from
milk, except as used for cooking purposes. An occasional glass of hot
milk taken as a stimulant for tired brain and nerves is sometimes
beneficial. Milk is composed of water, salts, fat, milk sugar or
lactose, albumen and casein. Average milk has from 8 to 10 per cent.
of cream. Good milk should form a layer of cream about 2-1/2 in. thick
as it stands in a quart bottle. Lactose (milk sugar) is an important
ingredient in milk. It is less liable to ferment in the stomach than
cane sugar. In the presence of fermenting nitrogenous material it is
converted into lactic acid, making the milk sour. Casein is present in
milk chiefly in its alkaline form, and in conjunction with calcium
phosphate. Milk absorbs germs from the air and from unclean vessels
very readily. Good, clean, uncontaminated milk ought to keep fresh,
exposed in a clean room at a temperature of 68° F., for 48 hours
without souring. If the milk is tainted in any way it will sour in a
few hours. Boiled milk will keep fresh half as long again as fresh
milk. Milk absorbs odors very quickly, therefore should never be left
in a refrigerator with stale cheese, ham, vegetables, etc., unless in
an air-tight jar. It should never be left exposed in a sick room or
near waste pipes. Absolute cleanliness is necessary for the
preservation of milk; vessels in which it is to be kept must be
thoroughly scalded with boiling water, not merely washed out with warm
water.
_Methods of Preserving Milk._
STERILIZED MILK.
Milk to be thoroughly sterilized and germ free must be heated to the
boiling point (212° F.). This may be done by putting the milk into
perfectly clean bottles and placing in a rack, in a kettle of boiling
water, remaining until it reaches the necessary degree of heat. The
bottle should be closely covered _immediately_ after with absorbent
cotton or cotton batting in order to prevent other germs getting into
the milk.
PASTEURIZED MILK.
The difference between pasteurizing and sterilizing is only in the
degree of heat to which the milk is subjected. In pasteurizing, the
milk is kept at a temperature of 170° F. from 10 to 20 minutes. This
is considered a better method for treating milk which is to be given
to young children, as it is more easily digested than sterilized milk.
All milk should be sterilized or pasteurized in warm weather,
especially for children.
CHEESE.
Cheese is one of the most nutritious of foods, and when meat is scarce
makes an excellent substitute, as it contains more protein than meat.
Cheese is the separated casein of milk, which includes some of the
fats and salts.
EGGS.
Eggs contain all the ingredients necessary to support life. Out of an
egg the entire structure of the bird--bones, nerves, muscles, viscera,
and feathers--is developed. The inner portion of the shell is
dissolved to furnish phosphate for the bones. The composition of a
hen's egg is about as follows (Church):--
----------------------+------------++---------------------+------------
| White--In || | Yolk--In
| 100 parts. || | 100 parts.
----------------------+------------++---------------------+------------
Water | 84.8 || Water | 51.5
Albumen | 12.0 || Casein and albumen | 15.0
Fat, sugar, | || Oil and fat | 30.0
extractives, etc. | 2.0 || Pigment |
Mineral matter | 1.2 || extractives, etc. | 2.1
| || Mineral matter | 1.4
----------------------+------------++---------------------+------------
The albumen--or the "white"--of an egg is greatly altered by cooking.
When heated beyond boiling point it becomes a very indigestible
substance. Eggs cooked at a temperature of about 170° F., leaving the
whites soft, are easily digested. A raw egg is ordinarily digested in
1-1/2 hour, while a baked egg requires from 2 to 3 hours. Eggs _baked_
in puddings, or in any other manner, form one of the most insoluble
varieties of albumen.
GELATIN.
Gelatin is obtained from bones, ligaments, and other connective
tissues. In combinations with other foods it has considerable
nutritive value. The place given to it by scientists is to save the
albumen of the body; as it does not help to form tissue or repair
waste it cannot replace albumen entirely. Gelatin will not sustain
life, but when used in the form of soup stock, etc., is considered
valuable as a stimulant.
* * * * *
LEGUMES--PEAS, BEANS AND LENTILS.
These vegetables contain as much protein as meat; yet, this being
inferior in quality to that contained in meat, they can scarcely be
given a place in the same class; therefore we will give them an
intermediate position in food value between meat and grains. From the
standpoint of economy they occupy a high place in nutritive value,
especially for outdoor workers. (See Recipes.)