Dairy Science
What is an antibiotic rapid test?
When there is a chance of antibiotic residues passing into milk it is important to be able to test for it quickly, since milk is a highly perishable product, so action is needed quickly. Milk can also not be worked into value added products like, yoghurt or cheese when it contains antibiotics, since the added lactic acid bacteria(LAB) will not grow in the presence of antibiotics. So for the producer of these products it not only limits the possibilities for the raw milk, but in case they miss the presence of the antibiotics, it could mean big losses.
It is thus of vital importance to be able to test for antibiotics as quickly as possible – even before the milk tanker is off loaded at the factory. When antibiotic milk received from one farmer is mixed with the mikl of other producers in the bulk tank, they will hold that farmer responsible for the loss of the entire bulk tank. It is thus in the interest of farmers to make sure that they do not supply antibiotic containing milk. This can easily happen through mis-management on the farm, in the case where a long-acting antibiotic is given in palce of a short acting antibiotic. The cow will be placed back into the milking sequence before all the antibiotic is out of the system and it will contaminate the entire batch.
Twinsensor that could test for tetracyclines and beta-lactames has evolved into the Trisensor.
Trisensor is brought to you by Unisensor Germany and is the latest rapid test that tests for Beta-Lactam, Sulfamides and Tetracycline in milk. This rapid test tests for 3 different families of antibiotics mainly used by farmers to control or prevent animal bacterial diseases.
Due to their human harmfulness and in respect to EU regulations, efficient controls of these antibiotics residues in food and especially in milk are needed.
The Trisensor test kit provides a multiplex dipstick test (Lateral Flow (LF) assay) that uses specific receptors and generic monoclonal antibodies. The results are visualized at the 3 specific capture lines by the use of colloidal gold-conjugates.
In this final version of the test, a fourth reagent line has been added to the dipstick, known as a “dynamic control line”. The intensity signal of this control line will proportionally increase with the sample/reagent flow migration. Therefore it reflects the correct use of the test, excludes potential invalid results and serves also to establish a threshold value limit for each test line result interpretation.
The test takes 6 minutes to run and does not require any cleaning or sample preparation. It is able to detect Limit of Detection(LoD) the 3 antibiotics at concentrations near their respective Maximum Residue Limit (MRL) values.
The results can be interpreted either through direct visual observation of the test and control or for a more “MRL-suitable” observation and result, an optical reader (Readsensor) can be used that suppresses any subjectivity from the operator and doesn’t need any calibration.
What makes this test different from the others is that it tests for Sulfamides. When ingested by humans side effects can include dizziness, drowsiness, nausea, vomiting, difficulty breathing etc. Unfortunately many South African farmers do not test for Sulfamides in milk samples and conform to EU principles regarding Sulfamides.
[audio:Antibiotic.mp3]
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If you are a commercial cheese maker and need help:
Go have a look at www.cheeseconsultants.com
Regards,
Leon the Milkman
Alizarol Test
1. ALIZAROL TEST
1.1 OBJECTIVE OF THE ALIZAROL TEST
The Alizarol test, due to its simplicity as well as its suitability to point out more than one defect of milk is a practical and well-suited procedure to test raw milk for acceptability, either on the farm or from the tanker at the factory. The main objective of the test is to indicate milk in which an unaccepted level of acidity has developed.
The stability of the protein complex in milk is destabilized by acid and therefore a positive alizarol test is also an indication of the heat stability of milk (i.e. the resistance of the protein complex against the denaturation by heat). The test is therefore also popular where the heat stability of milk proteins is of importance during processing, e.g. during the production of milk powder or UHT milk.
By adding the pH-indicator alizarine to the solution an indication of whether the milk is abnormally sour or alkaline can be obtained.
For an online training course on the alizarol test that you can use forever in your dairy business to re-train and train new employees at $45 go to:
1.2 FACTORS AFFECTING THE TEST
1.2.1 Acidity
The presence of lactic acid is the most important cause of a positive alizarol test. At the higher acid level (lower pH ) the protein suspension in milk will be less stable with the result that protein flocculation (coagulation) will occur when acid milk is mixed with alcohol.
Under normal circumstances and if the concentration of the alcohol is 68% (v/v), acidity will influence the test as indicated in Table 1.
TABLE 1 THE ALIZAROL TEST
TYPE OF MILK |
PH | %TA | FLOCCULATIONPROPERTIES | COLOUR |
| Fresh milk | 6.60 – 6.45 | 0.14 – 0.16 | None | Light purple |
| Slightly sour | 6.30 – 6.50 | 0.17 | Possibly small flakes | Brownish-pink |
| Sour | 6.00 – 6.20 | 0.18 – 0.19 | Small flakes | Brownish-pink |
| Very Sour | <6.00 | 0.20 + | Big flakes | Yellow |
| Sweet coagulation | 6.60 – 6.75 | 0.14 – 0.16 | Big flakes | Light purple |
| Mastitis | 6.80 + | N/A | Small flakes | Violet |
| Added alkaline | 6.80 + | N/A | None | Violet |
1.2.2 Mastitis
Mastitic milk differs from normal milk as regards, amongst others, the protein and mineral composition. These differences cause the casein (protein) to flocculate more readily in mastitic milk. As the pH of mastitic milk is normally higher than that of normal milk the alizarine colour will turn violet if such milk is tested.
1.2.3 Sweet curdling
Certain contaminating bacteria are capable of producing rennin like enzymes, which increase the viscosity of the milk and even flocculate casein in the absence of acid. This phenomenon is known as sweet curdling. Such milk can be identified by inoculating aseptically a small quantity there-off into sterilised milk and incubating the inoculated milk at room temperature for a day or more on which the viscosity of the milk will increase at the normal pH of fresh milk.
Large numbers of these bacteria e,g. 800,000 /ml milk was found to create a positive reaction in previously sterilised milk.
1.2.4 Mineral imbalance
Too high or to low a concentration of minerals such as calcium, phosphate and citrate will increase the ease with which casein will flocculate in the presence of alcohol.
This aspect is complex and not well define. It is well known that the addition of very small amounts of Calcium (0.2 ml M/4 Ca-acetate / 25 ml milk = 0.6g / 1 l melk ) and Magnesium (0.1 mlM/4 MgCl2 / /25 mlmilk = 0.95 g / 1l melk ) will normally result in a positive test while the addition of phosphate and citrate salts may alleviate the situation. In more extreme cases excess phosphate and citrate may however be the cause of a positive test.
Small variation e.g. 0.01% in the normal Calcium content of milk may influence the test.
It is claimed that in some instances supplementing a cows ration with mono-calcium phosphate e.g. 20 – 40 g /day / cow may improve the situation.
If a positive reaction is due to mineral imbalance a very slight souring of the milk, causing a portion of the colloidal fraction of the minerals to become soluble, may result in a negative test.
Heating of alizarol positive milk to 60°C for 30 minutes will cause partial precipitation of Ca3(PO4 ) and as result the test may turn negative.
1.2.5 Stage of laction;
The chemical composition of early and late lactation milk differs from that of normal milk
in the sense that it is characterised e,g. by higher levels of albumin, globulin and chloride.
Due to these differences the protein suspension in such milk is usually very
unstable against alcohol
Milk is normally very unstable to alcohol in early lactation, thereafter gradually becoming more stable and remaining at a fairly constant level of stability which is specific for each cow. Towards the end of lactation milks from some cows become more stable but a decrease in stability is more common.
1.2.6. Other factors that may cause alizarol positive reactions include;
- Irritation of the udder tisue.
- Infected uterus and vagina
- Aborsion
For an online training course on the alizarol test that you can use forever in your dairy business to re-train and train new employees at $45 go to:
1.3 PRINCIPLES OF THE TEST
The stability of the protein dispersion in milk is maintained by hydration (combining with water) and by the negative electrical charges on the protein particles. If either of these two factors under goes a change, the proteins will flocculate. Alcohol is a dehydrator and therefore destablises the protein. If the protein is already slightly unstable due to souring of the milk, dehydration with alcohol will lead to the precipitation of the protein in the form of flakes.
1.4 REAGENTS AND APPARATUS:
- Measuring equipment: E.g. 2 – 5ml pippettes, siringes or automatic measuring apparatus for measuring milk and alizarol.
- Test tubes, small containers or other apparatus for mixing milk and alizarol.
- Alizarol-solution: Either 68 % (v/v%) or other specified concentration (see Table 2) of ethanol with alizarin powder dissolved in the alcohol.
Alizarol must be kept in a brown bottle in a cool place.
Either methyl (white spirits ) or ethyl alcohol, standardized with water to specified concentration and containing 0.4g alizarin powder (1.2 – dioxy-anthrquinone – C14H8O4, MM 240.22, colour code: CI 58000, pH-reeks: 11.0 – 13.0). The pH of the mixture should be neutralized to 6.7 and checked regularly.
TABLE 2 APPLICATION OF DIFFERENT ALIZAROL CONCENTRATIONS
| Purpose of test | Concentration of alcohol | % Lactic acid for milk to curdle |
| To determine if milk will curdle without boiling. | 44 | 0.25 – 0.28 |
| Ordinary alcohol test. | 68 | 0.18 – 0.21 |
| More sensitive alcohol test. | 70 | 0.16 – 0.18 |
| To determine if milk can withstand high temperatures of condensing. | 75 | Milk will endure temperature treatment of 100 °C – 112 °C without curdling. |
1.5 THE PROCEDURE FOR DETERMINING PROTEIN STABILITY (ALIZAROL TEST)
(i) Equal volumes e.g. 2 or 5 ml of milk and alizarol of prescribe concentration, e.g. 70%, is mixed in a suitable container e.g. a test tube. (Equal volumes is critical for the accuracy of the test).
(ii) Mix carefully by inverting the tube once of twice.
(iii) Evaluate: – degree of flocculation, if any
– colour change
(iv) Interpretation
– If the colour remains light purple and no flocculation occurs, accept the milk.
– If the colour remains light purple and slight flocculation occurs, confirm acidity/ bacterial activity by performing one or more of the following tests:
- Clot-on-boiling
- pH and/or titratable acidity
- Resazurin test
– If the colour turns brownish-pink and flocculation occurs, reject the milk.
– If the milk has a brownish-pink colour but no flocculation occurs, determine the pH or %TA. If the results are unacceptable, that is, if they do not fall within the prescribed limits, reject the milk.
– If the colour of the milk varies from brownish-yellow to yellow, reject the milk.
– If the colour of the milk is violet but no flocculation occurs, determine the pH or %TA. If the results are unacceptable, that is, if they do not fall within the prescribed limits, reject the milk.
– NB! Take care not to interpret fat granules in cold milk for protein flocculation.
For an online training course on the alizarol test that you can use forever in your dairy business to re-train and train new employees at $45 go to:
Alizarol Test Kit Video
What is good about this alizarol test kit?
- Very small and handy
- only 400 microlitres of alizarol used per test
- Spring-loaded syringe makes sample taking easy
- Flip-cap bottle, so that cap cannot fall into milk or onto floor
- Can be washed and re-used few times to lower cost
Mozzarella stretching pH
The usual pH for stretching mozzarella curd is between 5 and 5.6, for buffalo mozz aim for 4.8 to 4.9(because of buffer efect from higher protein) and for artificially acidified mozz(like with citric acid) aim for 5.6-5.8
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Acidifying feta brine
Hi, Cheese fans
Most of the Feta brine recipes I have seen use citric acid to acidify the brine, but you can use any other household acid :-)Â , well like vinegar.
The first time I used the vinegar I thought that it would give a taste to the feta, but it did not – maybe you are more sensitive to the taste.
Also remember to test the acidity of the brine – if it is too alkaline your feta will dissolve in time. I use methyl red indicator to test the acidity. If it turns pink it is acid enough and if it turns yellow, you need more acid.
Drink your milk and eat your cheese 😉
Leon the Milkman
Enzymes in milk
Hi, Milk Fans
Milk contains a number of enzymes, that include lipase, protease, alkaline phosphatase, acid phosphatase, esterase, xanthine oxidase, lactoperoxidase, catalase, aldolase and lysozyme.
Remember to drink your milk,
Leon the Milkman
Link to Meetse-Tech Labs
Hi, Milk Fans
I have just linked to www.meetse.co.za, the home of Meetse-Tech Labs in South Africa. They are a lab specialising in dairy, water and soil analysis near Benoni, South Africa. They also import fine Funke Gerber dairy science equipment.
Check them out while you are drinking your milk,
Leon the Milkman
Curd Cooking?
Hi, Cheese Fans
The expulsion of whey during the cheese making process is hastened by heating and stirring. This heating is called “Cooking the Curd” by cheese makers. This is usually a gradual process that ranges from 33°C(91.4°F) to 80°C(176°F). If the heating takes place too fast the curd particles become overfirm on the outside – known as “case hardening” – preventing moisture and lactose to be released. This could give an over-acid cheese.
Remember: Drink milk!
Kind regards,
Leon the Milkman
Whipping Cream
Hi, Dairy Fans
Cream will whip if the fat content exceeds 30% and if the cream is cold, because the fat has to be in a solid state. The cream must have been cold for some time to allow complete crystallization of the fat.
Remember: Drink Milk!
Kind regards,
Leon the Milkman
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