Meat and meat product's quality is one of the most important branches of veterinary medicine.
So, researchers do their best to get meat with high keeping quality in addition to its high palatability properties, including visual appearance, smell, firmness, juiciness, tenderness, and flavor.
Dr.provet decided to focus on many points in meat production using Q&A form.
This article includes:
- What's the use of the malachite green test? And How to perform it?
- Using nitrite in meat curing is considered a double-edged weapon, explain.
- White crystalline bloom (efflorescence) on the surface of fermented sausages is an undesired phenomenon, discuss the reasons.
- Enumerate the methods of meat preservation and discuss two of them.
- How to detect the antibiotic residues in my meat?
Q 1: What's the use of the malachite green test? And How to perform it?
It's a laboratory test used to determine whether the meat (the meat product) was from a dead animal or slaughtered animal.
This test depends mainly on the fact that a scientific abattoir practice ensures well bleeding with slaughtering.
Meat from a slaughtered animal has less blood content because more than 50% of blood is lost during bleeding as in the halal slaughtering method.
But if an animal is slaughtered after its death, the bleeding will be poor, so a high volume of blood will remain in the internal organs and blood vessels.
The procedure for the malachite green test
- Place 6 g of fat-free muscle cut in 14 ml water, and leave to stand for 15 min.
- Withdraw 0.7 ml of supernatant into an agglutination tube.
- Add 1 drop malachite green reagent, mix, add 1 drop H2O2, shake well, and allow standing for 20 min.
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Results
- In case of ill bleeding, a cloudy, green-colored solution is formed.
- But in case of well bleeding, a clear, blue-colored solution is formed.
Q 2: Using nitrite in meat curing is considered a double-edged weapon, explain.
Nitrite is used as a preservative for processed meat as it can:
- Prevent lipid oxidation.
- Remove moisture and reduce the water activity of the meat.
- Inhibit the action of Clostridium botulinum and so protect us from botulism.
- Preserve the characteristic color, texture, and flavor of cured meat products.
- Extend the shelf-life of the meat product.
But it has harmful effects on the human body, as N-nitrosamines formed after meat curing are carcinogenic to humans.
So, studies on the potential usage of plant-based alternatives for nitrites in meat products are performed.
Nitrite-free meat products such as salami have been prepared by using curing systems consisting of the preformed cooked cured-meat pigment, CCMP (an antioxidant, a sequestrated, and an antimicrobial agent).
The color, flavor, and oxidative stability of the cooked treated products, as determined by Hunter L, a, b values, sensory means, and 2-thiobarbituric acid (TBA) test respectively, were similar to those in nitrite-cured products.
Using a gas chromatography-thermal energy analyzer (GC-TEA) methodology confirms the absence of N-nitrosamines in the nitrite-free cooked products.
Q 3: White crystalline bloom (efflorescence) on the surface of fermented sausages is an undesired phenomenon, discuss the reasons.
The appearance of the efflorescence is mainly related to the water activities of the sausages in the range of 0.81- 0.88 during packing and storage conditions.
Different types of the crystal can be found in dry-fermented sausage, including:
- The major component of efflorescence on dry fermented sausages is magnesium-di-lactate which is mainly related to the presence of lactic acid bacteria (Pediococus pentosaceus and Lactobacillus Plantarum) and low pH.
- Sodium chloride (linked to fast dehydration and water activity below 0.75 on the surface. Salt concentration will be under the limit of solubility).
- Other types of crystals less common on the surface of the casing are creatine and tyrosine ones. Also, phosphate crystals are not uncommon (of course, only in case that phosphates have been used as additives and the pH is a bit higher than the common one in fermented sausages.
Q 4: Enumerate the methods of meat preservation and discuss two of them.
Meat can be preserved by many techniques, including :
- chilling
- freezing
- curing
- smocking
- Thermal processing
- canning
- dehydration
- irradiation
- chemical additives
- pressure processing
Meat chilling (flash Freezing)
It's the exposure of meat to rapidly chilling to reduce the Bacterial growth risk.
The chilling of meat occurs in cold chambers with specific properties, including:
Temperature:1 - 4 C degree for primary chilling, but generally it shouldn't be below -1 C degree to avoid
Ice crystals formation.
Airspeed: 0.25 - 3 m/s (0.75 - 1.5 m/s in the empty part of the chamber).
Relative humidity: 90 — 95%, but it's difficult to control this factor.
Advantages of the chilling:
Reducing bacterial growth, and so protects the meat from spoilage.
Minimizing the weight loss that occurs as a result of evaporation.
Inhibition of hemoglobin oxidation and so it reduces the discoloration of the surface.
But on the other hand, the preservation of the meat by chilling has some disadvantages, the major one of them is cold shortening when the meat is chilled immediately after slaughtering before conversion of glycogen to lactic acid.
This undesirable phenomenon makes the meat tougher, and it's more common in beef and mutton.
Meat freezing
It's a technique that depends mainly on exposure of the meat to deep-freezing.
This technique is recommended when a very long preservation period is required, especially when preserved meat is intended for further processing or export.
It requires around -30c degree temperature, 150 - 300 m/s air circulation, and 95% relative humidity to avoid dehydration.
The advantages of meat freezing
This method of preservation is recommended as it has some advantages, including :
It's a technique with minimal preparations.
It keeps meat quality longer, which may reach 6 - 12 months for roasts and steak.
Likewise, it reduces the enzymatic activity and so it stops the growth of mold and bacteria.
Disadvantages of freezing
It neither causes' sterilization nor tenderization of the meat.
Formation of ice crystals with slow freezing.
It may cause freezer burn and loss of meat juices during thawing.
Q 5: How to detect the antibiotic residues in my meat?
When sick farm animals are treated with antibiotics, antibiotic residues are found in the animal’s tissue.
Human consumption of meat with antibiotic residues over the maximum residue limits (MRL) may have a risk for human health, including carcinogenic, toxic, or allergenic effects in addition to the antibiotic resistance which may be induced.
Detection of antibiotic residues in meat
- Microbial screening method
This method depends mainly on the microbial inhibition assay that can use only one test to cover an entire antibiotic spectrum.
The microbial inhibition assay can be performed either by the tube test or the plate test.
In the tube test, a tube containing a growth medium is used, then it's inoculated with spores of certain bacteria, and supplemented with a pH.and so, the acid produced by the growing bacteria leads to the presence of colored solution in the test tube.
The absence or change of this color indicates the presence of antibiotic residues.
In the plate test, the sample is spread on the layer of the plate containing inoculated nutrient agar and so, there is an opaque layer formed by bacterial growth.
The presence of antimicrobial residues is detected by a clear growth-inhibited area around the sample.
- CAST (Calf Antibiotics and sulfonamides test)
A microbial inhibition screening test is used to detect antibiotics and sulfonamides in calf carcasses.
The test uses Mueller Hinton agar as the growth medium and Bacillus megaterium ATCC 9885 as the indicator organism.
- Immunological technique
The immunological tests depend mainly on the principle of antigen-antibody interactions.
- ELISA test
The major immunological test is the ELISA test that allows accurate quantification of certain antibiotics.
- STOP (Swab test on Premises)
In this test, a population of bacteria is added to the sample. If the sample has antibiotic residues, there is no bacterial growth observed.
This test allows low-cost screening for a wide range of antibiotics residues.
This method is easy and can be performed directly on-site at the breeder, at the slaughterhouse.
The antibiotic residues can also be detected in both porcine and bovine urine regularly using the urine sample for this method.
- Chromatographic method
Chromatography is very effective in the qualitative and quantitative screening of antibiotic residues in food animals.
This method includes:
- The high-performance liquid chromatography (HPLC)
HPLC Is an effective method to analyze multiple residues in the meat sample within a short time.
A combination of HPLC with mass spectrometry (MS-MS) results in a great decrease of analysis time for confirmation in positive samples after initial screening.
- Thin-layer chromatography (TLC)
TLC is a separation technique that depends mainly on the differential partitioning of compounds between a solid surface, coated with a thin layer.
- Biosensors
This is a recent approach to detect residues in meat and ensure its quality and safety.
The instrument is made of a biological recognition element (bioreceptor), which recognizes the target antimicrobial residue, and a signal transduction element (transducer) which converts the recognition event into a measurable signal.
It is finally connected to data acquisition and processing systems.
A bioreceptor may be an organic molecular species such as an antibody, nucleic acid, enzyme, and protein. Or a living biological system such as cells, tissues, or whole organisms.
Types of biosensors
There are different types of biosensors, including:
- Enzymatic biosensors
They are commonly used for the analysis of herbicide contaminants.
It also was developed to detect penicillin.
- Cellular biosensors
They are used to detecting antibiotic residues such as tetracycline, quinolones, beta-lactam antibiotics, and chloramphenicol.
Written by: Dr. Mai Foda
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