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Файл:Veterinary and sanitary examination of meat and meat products. Study aid
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Fig. 4. Walpole comparator
To prepare a 1:4 extract, weigh out a sample of meat weighing 10 g, finely
chop it with scissors, grind it in a porcelain mortar, add a little water from a total
amount of 40 cm3. The contents of the mortar are transferred to a flat-bottomed flask,
the mortar and pestle are washed with the remaining amount of distilled water, which
is poured into the same flask. The flask is capped, the contents are shaken for 3
minutes, after that it stands for 3 minutes, then shaken again for 2 minutes. The
extract is filtered through 3 layers of gauze and then through a paper filter.
First, the pH is approximately determined to select an indicator. To do this,
pour 1–2 cm3 of extract into a porcelain cup and add 1–2 drops of a universal
indicator. The color obtained by adding the indicator is compared with the color scale
provided in the kit. If the reaction of the medium is acidic (as is usually the case with
meat extracts), use the indicator paranitrophenol; if the reaction is neutral or alkaline,
use metanitrophenol.
pH is determined using a standard set of colored liquids in sealed test tubes and
a Walpole comparator. In a comparator with 6 nests, place test tubes filled as follows:
- in nests No. 1 and No. 3 — test tubes with 2 cm3 of extract and 5 cm3 of
distilled water;
- in slot No. 2 — a test tube with 2 cm3 of extract, 1 cm3 of paranitrophenol
indicator and 4 cm3 of distilled water;
- in nest No. 5 — a test tube with 7 cm3 of distilled water.
In slots No. 4 and No. 6, standard test tubes with colored liquids from the
Michaelis set are selected so that the color intensity of their contents coincides with
the color intensity of the contents of the test tube in slot No. 2 (with an indicator).
The pH value of the extract under study will correspond to the number indicated on
the standard test tube. If the color shade of the liquid in the test tube with the extract
under study occupies an intermediate position between the shades of the contents of
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two standard test tubes, then the average pH value indicated on the test tubes with
these solutions is taken.
Determination of volatile fatty acids in meat
Deamination of amino acids during meat spoilage leads to the formation of
fatty acids, most of which are volatile. The amount of volatile fatty acids is
determined by distilling them from an acidified aqueous extract of the product with
live steam, followed by titration of the distillate.
Analysis order
The analysis is carried out using the steam distillation apparatus shown in Fig. 5.
Fig. 5. Device for distillation of VFA with water vapor:
1 — round-bottomed flask; 2 — plug; 3 — refrigerator;
4 — conical flask; 5 — steam generator flask
A sample of crushed muscle tissue weighing 25 g is placed in a round-
bottomed flask (1) with a capacity of 0.75–1.0 dm3. 150 cm3 2 % sulfuric acid
solution is also poured there. The contents of the flask are mixed and the flask is
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closed with a stopper (2). A conical flask (4) with a capacity of 250 cm3 is placed
under the refrigerator (3), on which the volume of 200 cm3 is marked. Distilled water
in a flat-bottomed steam-forming flask (5) is brought to a boil and volatile fatty acids
are distilled off with steam until 200 cm3 of distillate is collected in the flask (4).
During distillation, the flask with the sample (1) is heated.
The resulting distillate in a flask (4) is titrated with a 0.1N solution of
potassium or sodium hydroxide with phenolphthalein indicator until a crimson color
appears that does not disappear within 30 s.
Simultaneously, under the same conditions, a control experiment is carried out
to determine the consumption of alkali for titration of the distillate with reagents
without meat.
The VFA content in meat is calculated using formula (1):
(V — V1) К 5.61 100
Х = , (1)
M
where:
X is the amount of VFAs in 100 g of meat in terms of the amount of alkali used
to neutralize them, mg KOH;
V is the amount of 0.1N solution of potassium hydroxide consumed for the
titration of 200 cm3 of meat distillate, cm3;
V1 is the amount of 0.1N solution of potassium hydroxide consumed for the
titration of 200 cm3 of distillate of the control experiment, cm3;
K — correction to the titer of a 0.1N solution of potassium hydroxide;
5.61 — the amount of potassium hydroxide contained in 1 cm3 of 0.1N
solution, mg;
M — sample mass, g.
The arithmetic mean of three parallel determinations is taken as the test result.
The calculation is made with an error of no more than 0.01 mg KOH.
In fresh meat, the VFA content is up to 4 mg KOH per 100 g of product, in
meat of questionable freshness — from 4 to 9 mg KOH per 100 g, in stale meat —
more than 9 mg KOH per 100 g of meat.
Determination of muscle tissue peroxidase activity
Peroxidase is an enzyme in muscle tissue; its activity depends on the pH of the
medium and the content of oxidizing substances in the extract, as a result of which
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complete correspondence between the benzidine reaction and the concentration of
hydrogen ions is not observed. Nevertheless, at a pH value of the extract
corresponding to fresh meat, the reaction with benzidine is in most cases positive, and
at a pH value corresponding to stale meat, it is negative.
The essence of the reaction is that peroxidase found in meat decomposes
hydrogen peroxide to form oxygen, which oxidizes benzidine. When benzidine is
oxidized, paraquinone diamide is formed, which in turn, with unoxidized benzidine,
forms a blue-green compound that turns brown.
Analysis procedure
For biochemical studies, a concentrated aqueous extract is prepared in a ratio
of meat and water of 1:4.
Weigh out a sample of meat weighing 25 g, finely chop it with scissors, grind it
in a porcelain mortar and add a little water from a total amount of 100 cm3. The meat
pulp is transferred into a flask, the mortar is washed with the remaining amount of
distilled water, which is poured into the same flask. It is closed with a rubber stopper
and shaken for 3 minutes, then left for 2 minutes and again shaken for 2 minutes. The
extract is first filtered through 3 layers of gauze, and then through a paper filter.
2 cm3 of aqueous meat extract (1:4) is poured into a test tube, 5 drops of a
0.2 % alcohol solution of benzidine are added, the tube is shaken and 2 drops of 1 %
hydrogen peroxide solution are added.
Extract from fresh meat gives a positive reaction — it immediately acquires a
blue-green color, turning into brownish-brown after a few minutes.
An extract from meat of questionable freshness gives a weakly positive
(dubious) reaction — a blue-green color appears late and quickly turns brown.
Extract from stale meat gives a negative reaction — there is no blue-green
color, and a brown-brown color immediately appears.
Reaction to primary protein breakdown products
in broth with copper sulfate
The method is based on the precipitation of water-soluble protein breakdown
products from the broth with copper sulfate, which accumulate in muscle tissue when
meat spoils.
Preparation of the broth. A sample of muscle tissue weighing 20 g is ground
into mince, placed in a flask, filled with 60 cm3 of distilled water, covered with a
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watch glass and placed in a boiling water bath for 10 minutes. The flask is cooled to
room temperature under running water, the hot broth is filtered through a dense layer
of cotton wool, that is at least 0.5 cm thick, into a test tube, placed into a glass with
cold water.
Analysis procedure
2 cm3 of filtrate is poured into a test tube and 3 drops of a 5 % solution of copper
sulfate are added. The test tube is shaken, placed in a stand, and after 5 minutes the
reaction results are assessed.
The meat is considered fresh, and the reaction is negative if the contents of the
tube remain transparent.
Meat is considered to be of questionable freshness, and the reaction is
questionable if the broth becomes cloudy, and the broth from frozen meat becomes
intensely cloudy with the formation of flakes.
Meat is considered stale, and the reaction is positive if a jelly-like clot forms in
the broth, and large flakes form in the frozen meat broth.
Reaction to ammonia and ammonium salts with Nessler's reagent
When meat spoils, protein breakdown products accumulate in it, including
ammonia and ammonium salts, which with Nessler’s reagent forms
mercurammonium iodide, a yellow-brown compound.
Analysis procedure
Add 1 cm3 of meat extract (1:4) into a test tube and add 10 drops of Nessler’s
reagent. The contents of the test tube are shaken and the color change and
transparency of the extract is observed.
The meat is considered fresh, and the reaction is negative if the extract
becomes greenish-yellow in color, remains transparent or becomes slightly cloudy.
The meat is considered to be of questionable freshness, and the reaction is
questionable if the extract acquires an intense yellow color, significant turbidity is
observed, and for frozen meat, sedimentation is observed.
The meat is considered stale, and the reaction is positive if the extract turns
yellow-orange or orange, and the formation of large flakes that precipitate is
observed.
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Determination of amino-ammonium nitrogen content in meat
(according to A.M. Sofronov)
10 cm3 of filtered extract in a ratio of meat to water of 1:4 is poured into the
flask, 40 cm3 of distilled water is added and 3 drops of 1 % alcohol solution of
phenolphthalein. The extract is neutralized with a 0.1N solution of sodium hydroxide
until it turns slightly pink. Then 10 cm3 of formalin, neutralized with
phenolphthalein, is added to the flask, and the contents of the flask are titrated with a
0.1N sodium hydroxide solution to a slightly pink color.
Calculation of the amino-ammonium nitrogen content in muscle tissue is
carried out using formula (2):
А = 1.4 × V , (2)
where:
A is the content of amino-ammonium nitrogen in meat, mg/10 cm3 of extract;
1.4 — the amount of amino-ammonium nitrogen, equivalent to 1 cm3 of 0.1N
sodium hydroxide solution;
V is the volume of 0.1N sodium hydroxide solution used for the second
titration.
In fresh meat, the content of amino-ammonium nitrogen is up to 1.26 mg, in
meat of questionable freshness — from 1.27 to 1.68 mg, in stale meat — more than
1.68 mg per 10 cm3 of extract.
Microscopic examination of meat for freshness
Imprints are prepared from the superficial and deep layers of meat. To prepare
the impression substance, the surface of the meat is touched to the flabbed glass slide,
leaving an imprint on the glass.
To prepare an impression substance from the deep layers of meat, take pieces
of meat measuring 3 × 4 × 4 cm, burn them twice in alcohol, sterilizing surface, use
sterile scissors to cut out a piece measuring 1.5 × 2 × 2 cm from this sample and
touch the cut side to surface of a flammable glass slide.
The impression substances are dried in air, having previously marked their
location with a pencil on the glass, signed and fixed in the flame of an alcohol lamp.
Thus, 2 impression substances are prepared from the surface and deep layers of meat.
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Impression substances are Gram stained in the following order:
1) staining with gentian violet — 2 min;
2) rinsing with water;
3) treating with Lugol’s solution — until the print darkens (1–2 min);
3) Lugol's solution is drained;
4) treating with ethyl alcohol — until the stain comes off (0.5–1 min);
5) rinsing with water;
6) fuchsin staining — 2 min;
7) rinsing with water;
8) drying between sheets of filter paper.
When examining colored preparations-imprints, first visually assess the intensity
of their color, then do microscopy using immersion oil (magnification × 900), while
determining the qualitative composition of the microflora, and for prints from deep
layers of meat — the average number of microbial bodies in 25 random fields of view
of the microscope.
The evaluation of the research results is carried out in accordance with the
“Rules for veterinary inspection of slaughter animals and veterinary and sanitary
examination of meat and meat products.”
Prints from fresh meat are weakly colored; in the field of view of a microscope,
microflora is absent or detected in prints from deep layers up to 10 microbial bodies,
mainly cocci.
Imprint preparations from meat of questionable freshness are colored more
clearly; in the field of view of the microscope, the imprint contains up to 30 microbes —
cocci and rods — from a deep layer.
Imprints from stale meat are intensely colored; in the field of view of a
microscope, in an imprint from deep layers there are more than 30 microbial bodies,
mostly rods.
Rationale for veterinary and sanitary assessment
of meat depending on freshness
According to the “Rules for veterinary inspection of slaughter animals and
veterinary and sanitary examination of meat and meat products,” veterinary and
sanitary assessment of fresh meat is carried out on a general basis.
Meat of questionable freshness, after preliminary cleaning (removal and
disposal of altered areas) and, if necessary, washing, is processed into boiled sausages
or boiled.
Stale meat is disposed of.
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Test questions and assignments
1. In what cases is the degree of freshness of meat determined?
2. What degrees of freshness of meat do you know?
3. What organoleptic indicators are determined when testing meat for
freshness?
4. Describe the organoleptic characteristics of meat of questionable freshness.
5. What do you do with meat if, based on the results of an organoleptic test, it
is found to be of questionable freshness?
6. What are the pH values of muscle tissue of meat of various degrees of
freshness?
7. What are the results of the reaction with copper sulfate in broth fresh and
stale meat?
8. How much amino-ammonia nitrogen is contained in meat of varying degrees
of freshness (mg per 10 cm3 of extract)?
9. How many microbial bodies are contained in prints from deep layers of meat
of varying degrees of freshness?
10. What is done with meat if, based on the results of laboratory tests, it is
found to be of questionable freshness?
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CHAPTER 3. VETERINARY AND SANITARY EXAMINATION
OF POULTRY MEAT
Rules for sampling poultry meat for freshness testing
Poultry meat is taken in batches. A batch is any quantity of poultry meat of the
same type and category, the same date of slaughter, produced at one facility, issued
with one document on quality and a veterinary certificate.
To check the compliance of the quality of poultry meat with the requirements of
regulatory and technical documentation, a sample is taken from different places in the
batch in the amount of 5 % of the transport container from the volume of the batch.
From the sampling boxes, 3 samples (carcasses) are taken for organoleptic,
chemical and microscopic analyses. Based on the results of the organoleptic
assessment, a conclusion is made about the degree of freshness of poultry meat.
Poultry meat classified as of questionable freshness based on the results of
organoleptic evaluation is subjected to chemical and microscopic examination.
If the results of the organoleptic assessment differ from the results of chemical
and microscopic analyses, the poultry meat is subjected to repeated chemical studies
on 5 newly selected samples.
If parts of a poultry carcass are packaged in consumer packaging, then at least
three packaging units are selected for laboratory research. An average sample
weighing at least 500 g is taken from the weight parts of poultry carcasses.
For bacteriological analyses, 3 samples (carcasses) are taken from the sampling
boxes.
Each selected sample is packaged in polyethylene, cellophane or parchment
paper. The samples are placed in a common container (box, bag), which is then sealed.
From the moment of collection to the start of analysis, samples are stored at a
temperature from 0 to +2 °C for no more than 24 hours.
Determining the degree of freshness of poultry meat according
to organoleptic indicators
When assessing the good quality of poultry meat, the appearance and color of
the surface of the carcass, subcutaneous and internal fatty tissue, and the serous
membrane of the abdominal cavity are determined. Determine the smell in the
abdominal cavity, the surface layer of carcasses and the layer of muscles adjacent to
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the bones, the consistency and condition of the muscles on the cut. Assess the
transparency and aroma of the broth after cooking the chopped meat.
Preparing samples for analysis
Unpackaged frozen carcasses or parts are thawed at room temperature until a
temperature of 0 to 4 °C is reached in the thickness of the muscles at least 5 mm deep.
Defrosting of poultry carcasses or their parts in consumer containers is carried
out in water at a temperature of (30 ± 2) °C for 2–3 hours or at room temperature
until a temperature of 0 to 4 °C is reached in the thickness of the muscles at least
5 mm deep. The water is constantly stirred.
Determination of the appearance and color of the surface of the carcass,
subcutaneous and internal adipose tissue,
serous membrane of the thoraco-abdominal cavity
The appearance and color of the surface of the carcass, subcutaneous and
internal fatty tissue, and the serous membrane of the thoraco-abdominal cavity are
determined visually on a sample taken in accordance with the regulatory document.
The results of the analysis are compared with the requirements of the regulatory and
technical document for a specific type of poultry meat.
Determination of the consistency and condition of the muscles on the cut
On the surface of a part of a bird or carcass, in the area of the pectoral and hip
muscles, with light finger pressure create a hole and ensure its alignment.
The pectoral and hip muscles are dissected across the direction of the muscle
fibers.
To determine muscle moisture, filter paper is applied to the surface of the
muscle section for 2 s.
To determine muscle stickiness, touch the surface of the muscle section with
your finger.
Odor detection
The smell of the surface of the carcass and the abdominal cavity or its parts is
determined organoleptically directly during sampling. To determine the smell of the
deep layers, a muscle incision is made with a clean knife. Particular attention is paid
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