Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Veterinary and sanitary examination of meat and meat products. Study aid
.pdf
71
diagnosis. Therefore, trichinoscopy of the above material is carried out using
methods of special processing of sections.
Trichinelloscopy of corned beef
Since the muscle tissue of salted meat is usually denser, muscle cuts from
corned beef are made twice as thin as usual. The sections are crushed between the
glasses of the compressorium, after which the top glass is removed and a drop of
glycerin diluted in half with water or a drop of 5 % lactic acid solution is applied to
each section with a pipette. The sections are processed for 1 minute, after which the
top glass is applied and examined using the usual method. When the capsule or the
parasite itself is calcified (calcareous stones), trichinoscopy reveals granular opacities
of the capsule or dark masses of lime. To dissolve the latter, the sections are placed
for 2–3 hours in a 10 % solution of hydrochloric acid, after which living parasites or
the remains of their bodies can be detected. If the material being tested is very hard,
then the sections are made with a sharp knife (razor) or the muscle fibers are softened
by heating pieces of meat on a watch glass with a 5 % solution of caustic potassium
to a temperature not exceeding 45 °C for 10 minutes. After this, the preparations are
treated with glycerin according to the method described above.
Trichinelloscopy of frozen pork
Frozen pork is thawed before testing. Sections with a thickness of no more than
1.5–2 mm are prepared from it. They are placed on glass, covered with a second glass
on top and compressed in such a way that excess meat juice flows out. After this, the
top glass is removed and one drop of a 0.5 % solution of hydrochloric acid or a
solution of methylene blue (0.5 cm3 of a saturated alcohol solution of methylene blue
per 10 cm3 of distilled water) is applied to each section with a pipette. The processed
sections are covered with glass and examined with a trichinelloscope. Sections
treated with hydrochloric acid become transparent or acquire a gray color, and the
capsule looks like a silver rim. Sections treated with methylene blue are painted light
blue, the capsule is lilac-pink or blue, the larva is not painted.
Trichinelloscopy of smoked meat
(processing according to P.M. Yamshchikov)
The sections prepared in the usual way are crushed between the glasses of the
compressorium, after which the top glass is removed, and the sections are placed using
tweezers into a Petri dish or a small bath with a 1 % solution of red streptocide prepared
72
with a 5 % solution of sodium hydroxide solution, for 1–2 minutes. The solution of red
streptocide can be replaced with a 1 % solution of rivanol, quinacrine or tropiflamin.
After this, the sections are transferred for 1–2 minutes into a bath with a saturated
solution of methylene blue (15 g per 100 cm3 of 80 % acetic acid). Stained sections are
thoroughly washed in hot water (80–90 °C) until almost completely discolored and
placed in a compressorium. Trichinelloscopy is carried out using the usual method.
As a result of processing, muscle fibers are painted light yellow, Trichinella
capsules are bright green, and Trichinella are blue. In some cases, Trichinella is not
stained, but is clearly visible against the stained background of muscle tissue.
Using this method, you can also study salted and frozen meat.
To study sausages and smoked pork, sections are treated in Petri dishes with a
10 % solution of potassium hydroxide for 0.5–1 hour.
Trichinelloscopy of pork fat
Trichinella can be localized in subcutaneous adipose tissue, in which muscle
layers are not macroscopically visible. Lard without visible muscle layers is cut
through its entire thickness and sections are taken from the inner surface of the lard
along the line of its delamination (in areas of atrophied muscles).
A narrow sample 2–3 cm long is cut out from the separation line with a scalpel.
The same sample is taken from the surface of the back fat adjacent to the skeletal
muscles. From each sample, longitudinal sections 0.3–0.5 mm thick are made with a
razor. The sections are crushed between the glasses, then, removing the top glass,
1–2 drops of a 1 % solution of methylene blue are applied to the sections. The slides
are squeezed again, and the preparation is heated for 10–15 s on an alcohol or gas
burner until the sections clear (in this case, the connective tissue turns blue, and the
muscle tissue turns green-blue), after which they are examined.
Method of double staining of preparations. The sections flattened between the
glasses of the compressorium are removed and immersed for 1–2 minutes in a
saturated solution of sodium hydroxide, and then for 1–2 minutes in a saturated
solution of methylene blue. The stained sections are removed and washed in hot
water, after which they are examined microscopically using the usual method. With
this dyeing method, the tissues are painted light yellow, the Trichinella capsule is
painted bright green, and the Trichinella is colored intensely blue.
73
Biochemical research (trichinoscopy after artificial muscle digestion)
The method is based on the digestion of muscle tissue samples taken from a
batch of pork carcasses with artificial gastric juice and the detection of Trichinella
larvae in the sediment (digested mass).
Artificial gastric juice (AGF) is prepared according to the following recipe: tap
water at a temperature of 41–42 °C — 1 000 cm3; concentrated hydrochloric acid —
10 cm3; Edible pork pepsin (TU 10.02.01.111-89) when studying fresh meat and meat
products — 2.0 g, when studying salted, smoked meat and meat products, bacon —
10.0 g. When using medical pepsin, the dose is increased to 20.0 g.
Artificial gastric juice is suitable for use within 8 hours from the moment of
preparation.
When examining meat in carcasses, half-carcasses, quarters, blocks, as well as
smoked meats (during random control) and other types of products, the number of
cuts (weight of the sample) is determined in accordance with the general rules (see
p. 76 of this publication).
The sample is ground in a meat grinder with a grid diameter of 3–4 mm,
transferred to a conical flask of appropriate capacity and filled with ILS in a ratio of
1:15. The flask is placed in a thermostat at a temperature of 41–42 °C and kept for
5–7 hours, being stirred occasionally. 10 minutes before the end of digestion, stirring is
stopped.
After digestion is completed, brown or dark brown flakes remain in the sediment.
⅔ of the supernatant liquid is carefully drained from the flask, the sediment is
poured onto a hemispherical nylon sieve with a cell diameter of 400 microns,
installed in a glass funnel with a diameter of 90–120 mm, connected by a rubber tube
to a test tube with a capacity of 5 cm3.
The poured sediment is left to settle for 15–20 minutes, then the rubber tube is
closed with a clamp and the test tube is disconnected. The contents of the test tube
(sediment) are transferred in parts to a watch glass and examined under low (8 × 10)
magnification of a microscope or in a trichinelloscope.
To isolate trichinella larvae, the group digestion method in AVT-type
apparatus can be used.
Method of group testing of pork for trichinosis in the AVT apparatus
The research is carried out using an apparatus for isolating trichinella larvae
(AVT). It is a thermostated chamber with eight reactors built into it, designed to
74
digest muscle tissue with a special liquid. Each reactor has a stirrer driven by an
electric motor and a settling tank for collecting sediment.
To examine carcasses for trichinosis, muscle samples are taken using a group
method from the cruses of the diaphragm at the border of the transition of muscle
tissue into tendon. When examining pork carcasses obtained from animals from areas
where trichinosis is recorded, prepare a group sample with a total weight of up to
100 g — 5 g from 20 carcasses or less (2.5 g from each of the two cruses of the
diaphragm of one carcass). From pork carcasses coming from areas where trichinosis
has not been recorded over the past 8–10 years, prepare a group sample with a total
weight of up to 100 g — 1 g from 100 carcasses or less (0.5 g from each of the two
cruses of the diaphragm of one carcasses). The group sample is ground in a meat
grinder, and the minced meat is collected in a glass with a serial number
corresponding to the reactor number.
Tap water with a temperature of 40–42 °C is poured into the thermostatic
chamber of the device to the marked level and the electric heating element is
connected.
Warm (40–42 °C) water (2.5 dm3) is poured into each reactor. Immediately
before filling the reactor with minced group sample, 6 g of food-grade pepsin with an
activity of 100 thousand units and 30 cm3 of concentrated hydrochloric acid are added
to it. To mix the mixture, turn on the stirrer for 1 minute. Then add the crushed group
sample and turn on the mixer for 45 minutes. The duration of digestion is controlled
using a time relay. The remaining reactors are loaded in the same sequence.
At the end of digestion, the time relay automatically turns off the stirrer. After
settling the liquid in the reactor (for 15–20 minutes), open the clamp covering the
elastic settling tube, pour 1–1.5 cm3 of liquid with sediment onto a watch glass and
examine the sediment for the presence of trichinella under a microscope, magnifying
glass or in a trichinelloscope.
After each study, the spent liquid is drained through a settling tube, the reactor
is washed with hot (80 °C) water and prepared for subsequent work. At the end of the
shift, the reactors are washed with a detergent solution.
If one or more trichinella larvae are detected in the sediment, the test group of
pork carcasses is transferred to an alternate overhead track, divided into 8 groups of
12–13 carcasses (initial group sample from 100 carcasses) or 2–3 carcasses each
(initial group sample from 20 carcasses), samples are taken again and a repeat
trichinoscopy is performed using the group method.
Carcasses from the group that gave a positive result during repeated
trichinoscopy are examined individually in an AVT apparatus, identifying the carcass
affected by trichinella larvae.
75
Differential diagnosis of trichinosis
Capsule-forming trichinella must be differentiated from sarcocysts (micher
sacs) and microfinns, which are most often found in meat and meat products, as well
as from air bubbles and calculi. Differentiation is based on the morphology of the
pathogen and the structure of the capsule.
Trichinella has a lemon-shaped, round capsule, inside there is a spirally coiled
larva (or several larvae).
Sarcocysts have their own shell of a cylindrical or irregular shape; the cyst is
enclosed in its own thin shell and consists of chambers containing merozoites.
Microfinns, unlike trichinella, are located between muscle fibers and have a
diameter of up to 2 mm (much larger than trichinella). Calcified small Finns that died
at an early age have a round or oval shape and are distinguished by the presence of a
layered connective tissue membrane around the crushed parasite (Fig. 9).
Calcified misher sacs can be confused with calcified trichinella. Unlike the
latter, they come in different sizes, and their calcification begins from the center,
while sporocysts can be seen at the periphery of the sacs. Calcified misher sacs, in
addition to skeletal muscles, are also found in the heart muscle, while trichinella
never develops there.
а b
Fig. 9. Differential diagnosis of trichinella:
a — sarcocysts in muscles; b – microfinna
Lime stones can be of different sizes. Sometimes a dense connective tissue
membrane forms around the stones. When solid calcareous stones form, it is
impossible to detect Trichinella using compressor trichinoscopy.
Round or oval-shaped air bubbles with a sharp black edge around them blur or
disappear when the compressor glass is compressed.
To differentiate calcified trichinella from calcified sarcocysts and stones of nontrichinosis nature, sections are stained using the Yamshchikov method with additional
treatment on a glass slide with a 15 % solution of hydrochloric acid for 1–2 minutes
76
and rinsing with water. Sections are viewed under low anterior magnification of a
microscope.
Veterinary and sanitary assessment
of slaughter products with trichinosis
In accordance with the “Rules for the veterinary examination of slaughter
animals and the veterinary and sanitary examination of meat and meat products,” if at
least one trichinella is detected in 24 sections in the compressorium (regardless of its
viability), the carcass and offal having muscle tissue, esophagus, rectum, as well as
unidentifiable meat products, are sent for technical disposal. External fat (lard) is
removed and reheated for 20–25 minutes at a temperature of 100 °C. Internal fat is
released without restriction. Intestines (except rectum) after usual processing are
released without restrictions. The skins are released after the muscle tissue is
removed from them. The muscle tissue removed from the skins is subject to technical
disposal.
All cases of detection of trichinosis in pigs must be reported to the veterinary
and medical authorities of the areas from which the infected animal came.
Control questions
1. What types of animals suffer from trichinosis?
2. How are muscle tissue samples taken from animal carcasses for testing for
trichinosis?
3. What research methods for trichinosis do you know?
4. How is compressor microscopy of muscle tissue performed?
5. What is the essence of the group method of testing meat for trichinosis?
6. What to do if Trichinella larvae are found when examining pork carcasses
using the group method?
7. How does the Trichinella larva in muscles differ from Sarcocyst and
Microfinna?
8. How is the veterinary and sanitary assessment of slaughter products carried
out when Trichinella larvae are detected?
77
CHAPTER 8. VETERINARY AND SANITARY EXAMINATION
OF EDIBLE ANIMAL FATS
Rules for sampling edible animal fats for research
Spot samples are taken from different layers of each packaging unit using a
clean, dry sampler, probe, knife, or spatula. Sampling of fat from transport containers
is carried out at a depth of at least 50 cm from the surface.
From a batch of fat in briquettes, cups, jars and other consumer packaging, spot
samples are taken in quantities up to 50 g after opening or removing the packaging.
Point samples placed in a clean, dry jar constitute a pooled sample. The mass
of the combined sample must be at least 600 g.
The combined sample is sent to the laboratory, where the fat is melted to a
paste-like consistency by placing the jar in hot water and mixing thoroughly.
Determination of the quality of edible animal fats according
to organoleptic indicators
Organoleptic evaluation of fats is carried out no later than 24 hours from the
moment of sampling. Before testing, the sample is stored in a refrigerator at a
temperature of 0...+4 °C.
Smell and taste are determined in an average fat sample at a temperature of
20 °C. When determining taste, samples are not swallowed.
The consistency is determined by pressing the fat with a spatula at a
temperature of 15–20 °C.
The color of the fat is determined in reflected daylight scattered light. The fat
is placed on a plate of milk glass or a glass slide and spread in an even layer about
5 mm thick, after which the color and shade are determined.
To determine transparency, fat is placed in a test tube made of transparent
colorless glass so that after melting it occupies at least half of the test tube. The test
tube is placed in a water bath with a temperature of 60–70 °C, the fat is melted and
examined in daylight, diffused transmitted light.
If there are air bubbles in the fat, the test tube is allowed to stand in a water
bath at the above temperature for 2–3 minutes, after which the transparency is
determined.
Benign beef fat has a solid consistency and is light yellow or yellow in color.
Benign lamb fat has a solid consistency, white or slightly yellow in color. Benign
78
pork fat has a pasty consistency, white or yellowish in color. Fats have a specific
smell and taste and are transparent when melted.
If the freshness is questionable, fats acquire a gray color, sometimes with a
brown tint, a musty, rancid or stearic odor, and a sharp-bitter taste. When melted they
are cloudy.
Spoiled fats are dark gray in color, sometimes with a brown tint, and have a
pronounced musty or rancid odor. The surface of the fat is sticky; when melted, the
fat is cloudy.
Benign badger fat is light yellow in color, with a specific odor. Transparent
when melted.
Benign marmot fat is light yellow in color with a specific odor, liquid at room
temperature, transparent.
Spoiled badger and marmot fats are cloudy, with a pronounced rancid odor.
Laboratory methods for researching edible animal fats
Determination of acid number of fat
The method for determining the acid number of fat is described on pp. 34–35
of this book. The degree of freshness of animal fat, depending on the value of the
acid number, is assessed as follows: fresh, good-quality beef fat has an acid number
of 1.2–1.5; pork — no more than 3.0; lamb — no more than 3.5; fat of questionable
freshness — no more than 5.0; stale fat — more than 5.0.
Method for determining the peroxide value of fat
The method for determining the peroxide value of fat is described on pp. 35–36
of this publication. The degree of oxidative deterioration of fat, depending on the
peroxide value, is assessed as follows: fresh fat — up to 0.03; fresh, not subject to
storage — from 0.03 to 0.06 inclusive; questionable freshness — from 0.06 to 0.10;
stale — more than 0.10.
Reaction of fat with neutral red
Neutral red is an acid-base and redox indicator, the color of which is red in an
acidic environment, yellow in an alkaline environment, red-violet in an oxidized
state, and colorless in a reduced state.
79
In the process of fat spoilage, volatile fatty acids and carbon dioxide
accumulate in them, resulting in a shift in the pH environment to the acidic side. In
addition, compounds are formed that have strong oxidizing properties — peroxides,
hydroperoxides, free radicals, atomic oxygen, which oxidize neutral red, causing a
corresponding change in its color.
Analysis procedure
A sample of rendered fat weighing from 0.5 to 1.0 g is placed in a porcelain
mortar, filled with a neutral red solution, ground with a pestle for 1 minute and the
neutral red solution is drained. The remaining drops of liquid, if they interfere with
observation, are washed off with water and the color of the fat is observed. The
degree of oxidative spoilage of fat is determined according to the table 7.
Table 7
Assessing the freshness of animal fats depending on the results
of the reaction with neutral red
Fat coloring
Freshness level
pork and lamb
beef
From yellow with a greenish
tint to yellow
Yellow to brown
Fresh
Dark yellow to brown
Brown to brown-pink
Fresh, cannot be stored
Brown to pink
Brown-pink to pink
Of questionable freshness
From pink to red
From pink to red
Stale
Determination of moisture and volatile matter content in fat
The content of moisture and volatile substances in rendered fats is determined
by drying a sample of fat.
Analysis procedure
The glass cup is dried for 30 minutes at a temperature of (103 ± 2) °C, cooled
in a desiccator and weighed.
2–3 g of the test fat are added to a weighed glass, weighed and dried at a
temperature of (103 ± 2) °C to constant weight.
80
The first weighing is carried out after an hour, subsequent weighings after
30 minutes. Constant mass is considered achieved when the difference between the
last two weighings does not exceed 0.0002 g.
The mass fraction of moisture and volatile substances (X) as a percentage is
calculated using formula (5):
m0 — m1
Х = × 100 , (5)
m
where:
m0 is the mass of the cup with fat before drying, g;
m1 is the mass of the cup with fat after drying, g;
m is the mass of the test fat sample, g.
The final test result is taken as the arithmetic mean value of the results (X) of
two parallel determinations, the permissible discrepancy between which should not
exceed 23 % in relation to the arithmetic mean value.
Rationale for veterinary and sanitary assessment of edible animal fats
depending on the degree of goodness
Fresh, benign fats are released for sale without restrictions. They may be
stored for a period of time specified by the relevant standards or regulations.
Fats of questionable freshness are melted down and re-examined. The results
of the repeat study are considered final.
Stale fats are disposed of.
Test questions and assignments
1. What types of spoilage of edible animal fats do you know?
2. How are fat samples taken from shipping containers?
3. What indicators are determined during organoleptic examination of fats?
4. What chemical indicators are standardized by the scientific and technical
documentation for edible animal fats?
5. Describe the procedure for the reaction of fat with neutral red.
6. Describe the organoleptic and chemical characteristics of fat of questionable
freshness.
7. How do you deal with edible animal fats that are of questionable freshness
or stale?
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]