=537. Names Of Meats.=—The parts of the animal from which the meats are
taken have received distinctive names, which serve to designate the
parts of the carcass offered for sale. These names are not invariable
and naturally are quite different in many markets. In this country
there is some degree of uniformity among butchers in naming the meats
from different parts. The names in scientific use for the parts of
mutton, beef and pork are found in the accompanying illustrations.[542]
=538. Sampling.=—When possible the whole animal should constitute the
sample. The relative weights of blood, intestinal organs, hide, hoofs,
horns, bones and edible flesh are determined as accurately as possible.
The general method of preparing samples of animal products is given in
paragraph =5=.
[Illustration: FIG. 114.]
[Illustration: FIG. 115.]
[Illustration: FIG. 116.]
[Illustration: NAMES OF CUTS OF MEAT.]
The method of sampling employed by Atwater and Woods is essentially
that just noted.[543] The sample, as received at the laboratory, is
weighed, the flesh (edible portion) is then separated from the refuse
(skin, bones etc.) and both portions weighed. There is always a slight
loss in the separation, evidently due to evaporation and to small
fragments of the tissues that adhere to the hands and to the implements
used in preparing the sample. The perfect separation of the flesh from
the other tissues is difficult, but the loss resulting from this is
small. In sampling the material for analysis, it is finely chopped,
either in a tray or in a sausage cutter, and in each case is well mixed.
=539. Methods of Analysis.=—The general methods for the analyses of
food products are applicable to meats and animal products in general.
In the separation of the nitrogenous constituents the methods described
in paragraphs =411-414= are followed. It is not safe to estimate as
proteids the total nitrogen multiplied by 6.25, since the flesh bases
have much higher percentages of nitrogen than are found in proteid
matters. As indicated in paragraph =280= the complete extraction of
dried meats by ether is difficult of accomplishment. After a few hours
it may be assumed that the total extract will represent the fat,
although additional soluble matters are obtained by continuing the
process. The heat producing power may be calculated from the analytical
data secured. The methods which have been described in the preceding
pages will be found sufficient for guidance in the examination of
animal products, and the analyst will find them, when modified to suit
particular cases, adapted to the isolation and estimation of proximate
food principles.
The methods of analyses followed by Atwater and Woods are given
below:[544]
_Water and Water-Free Substance._—The drying is done in ordinary water
ovens at a temperature of nominally 100°, but actually at 96° and 98°.
For each analysis of animal tissues (flesh) one or more samples of from
fifty to one hundred grams of the freshly chopped substance are weighed
on a small plate, heated for from twenty-four to forty-eight hours,
cooled, allowed to stand in the open air for about twenty-four hours,
weighed, ground, sifted through a sieve with circular holes one-half
millimeter in diameter, bottled and set aside for analysis. In case of
fat samples which cannot be worked through so fine a sieve, either a
coarser sieve is used or the substance crushed as finely as practicable
and bottled without sifting.
For the complete desiccation, about two grams of material are dried for
three hours. It is extremely difficult to get an absolutely constant
weight, though it is found that this is in most cases approximately
attained in four hours.
_Nitrogen, Protein, Albuminoids etc._—The nitrogen is determined in
the partly dried substance by the method of Kjeldahl. The protein is
calculated by multiplying the percentage of nitrogen by 6.25. The
nitrogenous matters in meats and fish, _i. e._, in the materials which
have practically no carbohydrates, are also estimated by subtracting
the sum of ether extract and ash from the water-free substance, or
the sum of water, ether extract and ash from the fresh substance, the
remainder being taken as proteids, albuminoids etc., by difference.
While this is not an absolutely correct measure of the total
nitrogenous matter, it is doubtless more nearly so than the product of
the nitrogen multiplied by 6.25.
_Fat (Ether Extract)._—The fat is extracted with ether in the usual
manner. The point at which the extraction is complete is not always
easy to determine. For the most part, the extraction is continued for
such time as experience indicates to be sufficient, and then the flask
is replaced by another and the extraction repeated until the new flask
shows no increase in weight.
According to experience, the fat of many animal tissues is much more
difficult to extract than that of most vegetable substances. In
general, the greater the percentage of fat in a substance the more
difficult is the removal of the last traces. Dried flesh is frequently
so hard that the fineness of the material to be extracted seems to be a
very important matter.
_Ash._—Ash is determined by the method recommended by the Association
of Official Agricultural Chemists.
_Food Value—Potential Energy._—The food materials are not necessarily
burned in the calorimeter, but the fuel value of a pound of each of the
foods, as given in the tables, is obtained by multiplying the number of
hundredths of a pound of protein and of carbohydrates by 18.6 and the
number of hundredths of a pound of fat by 42.2, and taking the sum of
these three products as the number of calories of potential energy in
the materials.
More reliable results are obtained by using the factors obtained by
Stohmann; _viz._, 5731 calories for proteids, 9500 calories for common
glycerids, 9231 calories for butter fat, 3746 calories for pentose
sugars, 3749 calories for dextrose and levulose and 3953 calories for
sucrose and milk sugar.[545]
=540. Further Examination of Nitrogenous Bodies.=—It is evident
that both of the methods proposed above for the examination of the
nitrogenous constituents of meats are unreliable. If the total nitrogen
be determined and multiplied by 6.25 the product does not by any means
represent the true quantity of nitrogenous matter since the flesh bases
contain in some instances more than twenty-five per cent of nitrogen.
If, on the other hand, the water, ash and fat in a meat sample be
determined and the sum of their per cents be subtracted from 100, the
difference represents the nitrogenous bodies plus all undetermined
matters and errors of analysis. The assumption that meats are free
of carbohydrates is not tenable since glycogen is constantly found
therein and in horse flesh in comparatively large amounts. In a
thoroughly scientific analysis of meats, the nitrogenous bodies should
be separated and determined by groups, according to the principles
developed in paragraphs =411-414=. This process requires a great amount
of analytical work and in general it will be sufficient to make a
cold water extract to secure the flesh bases and a hot water extract
to secure the gelatin. The nitrogen is then determined in each of
these portions separately. The nitrogen in the cold water extract is
multiplied by four, in the hot water extract by six and in the residue
by 6.25. The sum of these products represents approximately the total
nitrogenous matter in the sample.
Aqueous extracts containing nitrogen are easily prepared for moist
combustion by placing them in the digestion flasks, connecting the
latter with the vacuum service and evaporating the contents of the
flask nearly to dryness. The sulfuric acid is then added and the
nitrogen converted into ammonia and determined in the usual manner.
=541. Fractional Analysis of Meats.=—A better idea of the composition
of a meat is obtained by separating its constituents into several
groups by the action of different solvents. This method has been
elaborated by Knorr.[546]
The separation of the meats in edible portion and waste and the
determination of moisture and fat are conducted as already described.
The residue from the fat extraction is exhausted with alcohol, and
in the extract are found the nitrogenous bases kreatin, kreatinin,
sarkin and xanthin, and urea, lactic, butyric, acetic and formic acids,
glycogen and inosit. In the residue from the alcohol extraction, the
proteid nitrogen is determined in a separate sample.
A separate portion of the sample is ground to a fine paste and
repeatedly rubbed up with cold water, which is poured through a tared
filter. When the extraction is complete, the filter and its contents
are dried and the dry residue determined. This residue represents
the nitrogenous constituents of the muscle fibers and their sheaths
together with any other bodies insoluble in cold water. The filtrate
from the cold water extraction is heated to boiling to precipitate
the albuminous matters which are collected, dried and weighed, or the
nitrogen therein determined and the albuminous matters calculated by
multiplying by the usual factor. The filtrate from the coagulated
albuminous bodies is evaporated to dryness and weighed. It consists
essentially of the same materials as the alcoholic extract mentioned
above. The ash and nitrogen in the aqueous extract are also determined.
The mean content of the edible parts of common meats, expressed as per
cents in groups as mentioned, follow:
Per cent.
Water 73.11
Ash 1.18
Total soluble matter 26.89
Phosphoric acid 0.49
Per cent.
{ Proteids insoluble in cold water 13.76
{ Of which coagulable by heat 2.24
Cold water extract 3.56
{ Ash in water extract 1.09
{ Of which phosphoric acid 0.38
Per cent.
Fat 4.93
Alcohol extract 3.03
Proteids in residue from alcohol 17.88
Total nitrogen in sample 3.37
=542. Estimation of Starch in Sausages.=—Starchy substances are
sometimes added to sausages for the purpose of increasing their weight.
The presence of starch in a sausage is easily detected by iodin. The
quantity may be determined by the following process:[547]
The principle of the process is based upon the observation that while
starch is easily soluble in an aqueous solution of the alkalies, it is
insoluble in an alcoholic solution thereof. The chief constituents of
meat, _viz._, fat and proteid matters, on the other hand, are readily
soluble in an alcoholic solution of potash or soda. This renders the
separation of the starch easy. The sample is warmed on a water bath
with a considerable excess of an eight per cent solution of potassium
hydroxid in alcohol whereby the fat and flesh are quickly dissolved.
The starch and other carbohydrate bodies, remain in an undissolved
state. In order to prevent the gelatinizing of the soap which is
formed, the mass is diluted with warm alcohol, the insoluble residue
collected upon a filter and washed with alcohol until the alkaline
reaction disappears. The residue is then treated with aqueous potassium
hydroxid solution, whereby the starch is brought into solution and,
after filtration, is treated with alcohol until it is all precipitated.
The precipitated starch is collected upon a filter, washed with alcohol
and finally with ether, dried and weighed. Starch prepared in this
way contains a considerable quantity of potash, the amount of which
can be determined by incineration. In order to avoid this trouble,
the starch, after separation in the first instance as above mentioned
and solution in aqueous potassium hydroxid, is precipitated on the
addition of enough acetic to render the solution slightly acid. The
precipitated starch, in this instance, is practically free of potash,
since potassium acetate is soluble in alcohol.
=543. Detection of Horse Flesh.=—Since horse flesh has become an
important article of human food and is often sold as beef and sausage,
a method of distinguishing it is desirable. The comparative anatomist
is able to detect horse flesh when accompanied by its bones, or
in portions sufficiently large for the identification of muscular
characteristics. It is well known that horse flesh contains a much
higher percentage of glycogen than is found in other edible meats.
Niebel has based a method of detecting horse flesh upon this fact, the
glycogen being converted into dextrose and determined in the usual way.
Whenever the percentage of reducing sugars in the dry fat-free flesh
exceeds one per cent, Niebel infers that the sample under examination
is horse flesh.[548]
The reaction for horse flesh, proposed by Bräutigam and Edelmann, is
preferred by Baumert. In this test about fifty grams of the flesh are
boiled for an hour with 200 cubic centimeters of water, the filtered
bouillon evaporated to about half its volume, treated with dilute
nitric acid and the clear filtrate covered with iodin water. Horse
flesh, by reason of its high glycogen content, produces a burgundy
red zone at the points of contact of the two liquids. In the case of
sausages, if starch have been added, a blue zone is produced, and if
dextrin be present, a red zone, both of which obscure the glycogen
reaction. The starch is easily removed by treating the bouillon with
glacial acetic acid. No method is at present known for separating
dextrin from glycogen. The detection of horse flesh is a matter of
considerable importance to agriculture as well as to the consumers,
especially of sausages. A considerable quantity of horse flesh is
annually sent to the market, little of which presumably is sold under
its own name. As a cheap substitute for beef and pork in sausages, its
use must be regarded as fraudulent, although no objection can be urged
against its sale when offered under its own name.[549]