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Файл:Veterinary and sanitary examination of meat and meat products. Study aid
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is fine-grained. The fat is gray in color, soft, of spreadable consistency, with
a specific odor.
Determination of the meat type by laboratory methods.
Method for determining the morphological structure of muscle tissue
The muscle fibers of different animal species have different lengths and
thicknesses. Therefore, in certain cases, these parameters can be used to determine
the species of meat.
Research methodology
A thin section is made along the muscle fibers with curved scissors, placed in a
compressorium or on a glass slide, split into individual fibers with a dissecting
needle, covered with another glass, crushed and examined under a microscope at low
magnification in a darkened field of view. During the study, the length and thickness
of the muscle fiber are visually determined:
- thick, short fibers — in bull, horse, camel meat;
- thick, long fibers — in a goat meat;
- thin, short fibers — in rabbit, dog meat;
- thin, long fibers — in a cow, ox, pig, cat meat.
Qualitative response of muscle tissue to glycogen
Glycogen is an animal sugar contained in muscle tissue; the amount of
glycogen in meat depends on the type of animal, gender, age, fatness, and location of
muscle fibers.
The essence of the qualitative reaction to glycogen is that it is detected by a
colored iodine test in muscle tissue broth if its content in the muscles is at least 1 %.
Approximately this amount of glycogen can be contained in horse, camel, dog, and
cat meat. At the same time, in old, sick animals, or animals after physical exercise,
the glycogen content in muscle tissue can be sharply reduced. Meat from the head
and neck of an animal also gives a negative reaction to glycogen. Meat from young
animals of all types gives a positive reaction to glycogen. Therefore, a qualitative
reaction does not always make it possible to determine the species of meat, but it can
be used to distinguish beef from horse meat, dog meat from lamb, rabbit meat from
cat meat.
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Analysis procedure
A sample of muscle tissue weighing 15 g is crushed, placed in a flask and filled
with 60 cm3 of distilled water. The contents of the flask are brought to a boil and
boiled for 30 minutes. After cooking, the broth is filtered and cooled to room
temperature. 3–5 cm3 of filtrate is poured into a test tube, 5–10 drops of Lugol’s
solution are added.
If the reaction is positive (glycogen content in the muscles is at least 1 %), the
broth turns cherry-red (the color of red wine). In most cases, horse, dog, and cat meat
gives a positive reaction to glycogen.
If the reaction is questionable, the broth turns orange (sometimes it’s a
characteristic of cat meat).
If the reaction is negative, the broth turns yellow (typical for beef, lamb,
rabbit, pork).
Determination of the melting and solidification point of fat
The melting and solidification temperature of fat and its consistency depend on
its chemical composition and, above all, on the ratio of saturated and unsaturated
fatty acids in it. The more saturated and less unsaturated fatty acids a fat contains, the
higher its melting and freezing point and vice versa.
Melting and solidification are reverse equilibrium processes. The solidification
temperature of fats is always slightly lower than their melting point (Table 1).
It is important to keep in mind that the melting and freezing temperatures
depend not only on the type of fat, but also on gender, age, nature of feeding,
condition of the animal before slaughter, location of the fat and its quality.
Analysis procedure
A piece of raw fat is placed in a test tube and melted in a water bath. Then the
melted fat is collected into a dry, clean capillary. The capillary is kept in the cold for
1–2 hours so that the fat hardens, and then attached to the thermometer using a rubber
ring so that they are at the same level. A capillary with a thermometer is placed in a
glass of water. The water level should be higher than the level of fat in the capillary,
and it, in turn, should not touch the bottom and walls of the glass. A glass of water is
heated and the condition of the fat in the capillary is observed. As soon as it
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completely melts and becomes transparent, its melting point is noted on the
thermometer (Fig. 1).
Fig. 1. Definition of the melting and solidification point of the fat
Without removing the capillary and thermometer from the glass of water, the
fat is allowed to solidify and, as soon as it becomes cloudy, its solidification
temperature is recorded on the thermometer.
The determination is carried out 2 times, the arithmetic mean is calculated,
which is taken as the melting and solidification point of the fat, and the difference in
the determinations should not exceed 0.5 °C.
Determination of the refractive index of fat
The refractive index (refraction) of fat depends on its chemical composition
(the amount of triglycerides, saturated and unsaturated fatty acids) and is a specific
indicator characterizing the fat of each type of animal (Table 1).
Analysis procedure
The refractive index of fat is determined using various types of refractometers
at a temperature close to its melting point.
Apply 2–3 drops of the test fat melted in a water bath to the measuring prism of
a refractometer pre-adjusted with distilled water and close the working chamber. The
illuminator directs a beam of light into the lighting prism and observes through the
eyepiece.
The chiaroscuro boundary is set at the crosshairs of the diagonal sighting lines.
The refractive index value of fat is read from the corresponding scale of the device.
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The melting and solidification temperatures of fat and the refractive index of
fat of various animal species are presented in Table 1.
Table 1
Values of the melting and solidification points and refractive index
of fat of various animal species
Type of fat
Melting point,
°C
Solidification point,
°C
Refractive index
(at temperature)
beef
42–45
27–35
1.451–1.458 (40 °C)
pork
30–40
26–30
1.458–1.461 (40 °C)
mutton
44–55
32–40
1.450–1.452 (60 °C)
goat
48–50
35
–
horse
15–39
10–30
1.459–1.466 (20 °C)
elk
47.5–48.5
30–35
–
canine
30–39
15–30
1,451 (20 оС)
rabbit
42.3
26,7
1,462 (40 оС)
feline
38.9–39.0
24.9–25.3
–
marmot
9–10
8
1.467–1.468 (40 °C)
badger
21–25
8–10
1.456–1.466 (40 °C)
Precipitation reaction with meat extract
The precipitation reaction is carried out to determine the type of meat. It is
based on the fact that when an antigen (precipitinogen) combines with specific
antibodies (precipitins) found in the corresponding serum, a precipitate is formed.
Antigens are obtained by extraction from the muscle tissue of the test sample; they
are mainly specific proteins of various animals.
The precipitation reaction is the most accurate method for determining the type
of meat. Using it, you can recognize the type of meat if it is preserved by salting, high
temperature, or is only present as an impurity in meat products.
Analysis procedure
First, an extract (precipitinogen) is prepared. To do this, a sample of the meat
being tested is freed from fat and connective tissue, grinded, placed in a flask and filled
with a double volume of saline. Raw meat is extracted for 3 hours, boiled, dried — up
to 24 hours. The extract is then filtered or centrifuged until completely transparent.
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0.5 cm3 of extract (precipitinogen) is poured into an Ulengut test tube and
precipitin (precipitating serum) in the same amount is added with a Pasteur pipette. If,
after 1–2 minutes, a sharply limited white ring or disk — precipitate — is formed at
the interface of precipitinogen and serum, the reaction is considered positive.
Control questions
1. In what cases is it needed to identify the meat type?
2. What types of meat falsification do you know?
3. What indicators are determined during organoleptic examination of meat?
4. How is the cooking test carried out?
5. What additional techniques used to determine the smell of meat do you
know?
6. What laboratory methods to determine the species of meat do you know?
7. The muscle tissue of which animal species consists of thin and long bundles
of fibers?
8. What does the refractive index of fat depend on?
9. In the muscle tissue of which animals does the glycogen content exceed 1 %?
10. What is the essence of the precipitation reaction?
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CHAPTER 2. VETERINARY AND SANITARY EXAMINATION OF MEAT
DETERMINING THE DEGREE OF FRESHNESS
During storage, meat may undergo undesirable changes (spoil), as a result of
which it loses its presentation, nutritional value and may be unsuitable for food
purposes.
The freshness of meat is determined in the following cases:
- when organoleptic signs of spoilage appear;
- when storing meat in the refrigerator for a long time;
- during forensic examinations.
To determine the degree of freshness of meat, the organoleptic method and
methods of chemical and microscopic examination are used.
In accordance with GOST 7269-2015, depending on the results of freshness
tests, meat can be:
- fresh;
- questionably fresh;
- stale.
Rules for sampling meat for freshness testing
Meat samples taken for the laboratory testing for freshness, are drawn from
each carcass or part of it in one piece weighing at least 200 g from the following
places: at the neck, against the 4th and 5th cervical vertebrae, in the area of the
shoulder blade; in the area of the thigh muscles.
Samples from frozen or chilled blocks of meat and offal or from individual
blocks of questionable freshness are taken in one piece weighing at least 200 g.
Each selected sample is packaged in food grade polyethylene film. On the label
inserted under the film, the name of the tissue or organ and the carcass number
assigned upon acceptance is indicated with a pencil.
Samples taken from the same carcass are packaged together in one bag and
placed in a metal lockable box. An accompanying document is also included there, it
indicates the date and place of sampling, the type of meat, the carcass number, the
reasons and purposes of the tests, and the signature of the sender of the material. The
box with the samples is sealed.
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Determining the degree of freshness of meat according
to organoleptic indicators
During organoleptic examination of meat, the following is determined:
- appearance and color of the surface of the carcass — visually;
- muscle moisture on the cut — tested with filter paper;
- muscle color on the section — visually;
- consistency — lightly pressured with fingers;
- smell — determined at a meat temperature of 15–20 °C; in difficult cases —
after applying a spatula heated in hot water to the surface of the meat and “piercing
with a pin” (see p. 8 of this publication);
- condition of fat — color of fat — visually, consistency of fat — when rubbed
between fingers;
- condition of the tendons — color — visually, elasticity and density — by
palpation;
- transparency and aroma of the broth — a sample of meat is passed through
a meat grinder with a grid hole diameter of 2 mm, the minced meat is thoroughly
mixed; 20 g of minced meat are placed in a conical flask with a capacity of 100 cm3,
60 cm3 of distilled water is poured, it mixed thoroughly, covered with a watch glass
and place in a boiling water bath; The smell of meat broth is determined during the
process of heating to 80–85 °C at the moment of the appearance of vapors escaping
from the slightly open flask.
To determine transparency, 20 cm3 of broth is poured into a measuring cylinder
with a capacity of 25 cm3, diameter 20 mm and the degree of its transparency is
visually determined.
A conclusion about freshness is made based on the results obtained in
accordance with the features presented in table 2.
Table 2
Organoleptic assessment of meat freshness
Index
Characteristics of meat
fresh
dubious freshness
stale
Appearance
and surface
color of the
carcass
It has a drying crust of pale pink
or pale red color, in thawed
carcasses it is red; the fat is soft,
partially colored bright red
Moistened in places,
slightly sticky, darkened
Very dried out,
covered with
grayish-brown slime
or mold
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Index
Characteristics of meat
fresh
dubious freshness
stale
Muscles on
the cut
Slightly damp, do not leave a wet
spot on the filter paper; color
characteristic of this type of
meat: for beef — from light to
dark red, for pork — from light
pink to red, for mutton — from
red to cherry red, for lamb —
pink
Wet, leave a wet spot on
the filter paper, slightly
sticky, dark red in color;
Thawed meat has
slightly cloudy meat
juice draining from the
cut surface
Wet, leave a wet
spot on the filter
paper, sticky, redbrown in color;
Thawed meat has
cloudy meat juice
draining from the cut
surface
Consistency
When cut, the meat is dense and
elastic; the hole, formed when
pressing with a finger, quickly
levels out
When cut, the meat is
less dense and less
elastic; the hole formed
when pressing with a
finger is leveled out
slowly (within 1
minute), the fat is soft,
in thawed meat it is
slightly loosened
When cut, the meat
is flabby; the hole,
formed when
pressing with a
finger, does not level
out, the fat is soft, in
defrosted meat the
fat is loose and
greasy
Smell
Specific for every fresh meat
type
Slightly sour or with a
hint of mustiness
Sour, or musty, or
slightly putrid
Condition of
fat
Beef — has a white, yellowish or
yellow color, the consistency is
hard, and crumbles when
crushed; pork — white or pale
pink, soft, elastic; lamb — has a
white color, thick consistency
It has a grayish-matte
tint, slightly sticks to the
fingers; may have a
slight greasy odor
It has a grayishmatte tint and
smudges when
crushed. Pork fat
may have a small
amount of mold on
it. The smell is
rancid
Tendon
condition
The tendons are elastic, dense,
the surface of the joints is smooth
and shiny. In thawed meat, the
tendons are soft, loose, and bright
red in color
The tendons are less
dense and matte white
in color. The joint
surfaces are slightly
covered with mucus
The tendons are
softened and grayish
in color. The joint
surfaces are covered
with mucus
Broth clarity
and aroma
Transparent, fragrant
Transparent or cloudy,
with an odor not typical
for the fresh broth
Cloudy, with a lot of
flakes, with a
pungent, unpleasant
odor
Determination of the degree of freshnessof meat by laboratory methods
Only meat that is recognized as being of questionable freshness based on the
results of organoleptic testing is subjected to laboratory (biochemical, microscopic)
studies.
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Determination of the pH value of muscle tissue
When meat spoils, organic bases accumulate in it as a result of decarboxylation
of amino acids, shifting the pH of muscle tissue to the alkaline side. Therefore, fresh
meat has a muscle tissue pH of 5.7–6.2, questionable freshness — 6.3–6.4, stale
meat — 6.5 and higher (in concentrated extracts).
In addition, the pH value of muscle tissue is determined when establishing the
condition of the animal at the time of slaughter and is used to determine appropriate
directions for meat processing. pH is determined when classifying meat into quality
groups — PSE (pale, soft, exudative — pale, soft, watery), DFD (dark, firm, dry —
dark, hard, dry), NOR (normal), measuring this indicator in fresh carcasses (2 hours
after slaughter) and chilled for 24 hours.
Potentiometric method
It is based on measuring the electromotive force of an element consisting of an
electrode, the potential of which is determined by the concentration of hydrogen ions
in the test environment. To determine pH, laboratory pH meters and portable express
meters are used.
Determining the pH of meat using a laboratory pH meter
Using laboratory pH meters, the active acidity of aqueous extracts of biological
objects and food products is determined.
Fig. 2. Diagram of the device for determining the pH value:
1 — voltage meter; 2 — reference electrode; 3 — glass electrode;
4 — glass, permeable to hydrogen ions; 5 — analyzed solution
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A laboratory pH meter (Fig. 2) consists of an indicator (glass) electrode, the
potential of which is determined by the concentration of hydrogen ions in the test
solution, a reference electrode with a known potential value, and a voltage meter unit
with a pH value scale (display).
Using a laboratory pH meter, the value of the indicator in aqueous extracts of
meat is determined.
To prepare an aqueous extract of meat, 10 g of minced muscle tissue is placed
in a flask, poured with 40 cm3 of distilled water and left for 30 minutes with periodic
stirring of the contents of the flask. Then the extract is filtered through a paper filter
and the pH value in the filtrate is determined.
The electrodes are placed in the extract being tested and after 2–3 minutes a
reading is taken from the instrument scale.
pH determination using a portable express meter
A portable pH meter consists of a voltage meter block and a knife-electrode
(Fig. 3), into which an indicator electrode, a reference electrode and a thermal
compensator, designed to correct the pH value for the temperature of the product, are
mounted. The knife-electrode is inserted all the way into the cooled or thawed muscle
tissue and after 2–3 minutes the pH value of the product is read off the device scale.
Fig. 3. Knife electrode for determination Meat pH (included in the portable pH meter kit)
Colorimetric method
To determine pH, a Michaelis kit with standard one-color solutions in test
tubes and a comparator is used (Fig. 4). First, prepare an aqueous extract from meat
at a ratio of 1:4 or 1:10.
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