University of KentuckyCollege of Agriculture
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Regulatory Services Milk Lab

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Detailed Descriptions: Milk Component Analysis and Test Capabilities

Analyst performing milk component
and SCC testing with the CombiFoss™ FT+

Electronic instrumentation:
FOSS CombiFoss™ FT+
The CombiFoss™ FT+ is a combination instrument consisting of the MilkoScan™ FT+ and the Fossomatic™ FC. The MilkoScan™ is an infrared based milk analyzer that determines milk components (i.e. fat, protein, lactose, total solids and solids-non-fat) and provides screening for freezing point depression. The Fossomatic™ FC provides us with automatic counting of milk sample somatic cells. This combination electronic instrument gives us the capacity to analyze a large volume of milk samples for routine component and somatic cell count testing.


Analyst performing milk component
testing with the MilkoScan™ FT 120

Foss MilkoScan™ FT 120
This electronic instrument provides us the ability to quickly analyze milk samples for components (i.e. fat, protein, lactose, total solids and solids non-fat). MilkoScan ™ FT 120 employs the Fourier transform Infra-Red Spectrophotometer (FTIR) measuring principle. In basic terms, the instrument provides milk component results through infrared light measurement. The Foss MilkoScan ™ FT 120 can provide test results in about 30 seconds and can be calibrated for raw bovine and caprine milk, homogenized milks, cream, whey and other dairy products.


Analyst adding DI water to Babcock bottles
prior to centrifugation

Milk Component Chemistry
Babcock Method for Fat

This is relatively inexpensive test for fat that can be performed on raw milk and a limited number of dairy products. This procedure uses sulfuric acid to “burn everything in the milk sample” except for the fat.  The remaining fat in the sample is then centrifuged and determined graduated markings on specialized glassware. The procedure is limited in that individual samples can only be read to the 0.05% fat level.


Analyst preparing Gerber bottle
for centrifugation

Gerber Method for Fat
This is a test is close relative to the Babcock method. It is often referred to as Babcock’s European cousin as this test is most common in the European dairy industry.  Milk fat is separated from other milk components by adding sulfuric acid. The separation is facilitated by using amyl alcohol and centrifugation. The fat content is read directly via a special calibrated butyrometer. The procedure is limited in that individual samples can only be read to the 0.05% fat level.


Centrifugation of ether flasks.

Mojonnier (Ether Extract) Method
This is the chemical method of choice for total milk fat because of its inherent analytical capacity. It can provide a very precise measurement of milk fat.  Because of its precision, the ether extraction procedure is the preferred chemical reference method for milk fat. Ether and alcohol are used to extract the fat from milk.  The ether extract is decanted into a dry weighing dish and the ether is evaporated.  The extracted fat is then dried to a constant weight and is expressed as % fat by weight.


Regulatory Services utilizes the Foss
Tecator™ 2400 Kjeltec Analyzer Unit
to perform Kjeldahl analysis

Kjeldahl Method for Protein
This chemical method determines the nitrogen content of milk. Acid digestion of the milk sample occurs at high temperature. Nitrogen content is then converted by known formula to provide the milk protein%.

Direct Forced Air Oven Method for Total Solids
Total solids are determined by weighing milk, drying milk and weighing the dried milk residue.  The sample is dried in a forced air oven for 4 hours at 100 + 1°C.  The total solids content of milk is the weight of dried milk expressed as a percentage of the original milk weight.

Somatic Cell Counts

Electronic Somatic Cell Count (ESCC) with the FOSS Fossomatic™ FC
This electronic instrument is used in the detection of somatic cells in the milk. Its working principle is based on coloring the somatic cells followed by counting the cells. The instrument’s measuring principle is known as flow cytometry and is based on the principle of passing a very thin string of the milk sample under a counting unit. The diameter of the string is so small that it only allows one somatic cell to pass at a time. Prior to passing into the flow cell, the milk is mixed with a fluorescent dye which dyes the DNA molecules present in the somatic cells. As the sample passes under the counting unit, it is exposed to blue light. The light “excites” the dyed cells causing them to emit red light, thus making it possible for the instrument to count the cells.
(Note: see also FOSS CombiFoss™ FT+ at the top of this page.)

Direct Microscopic Somatic Cell Count
The SCC is determined by viewing stained somatic cells under a microscope under oil immersion. The analysts’ estimated counts are determined by using a microscopic factor based on the field of view of the microscope. 

Cryoscope Instrument

Other Tests of Milk Quality

Freezing Point Depression (FPD) of Milk with the Cryoscope
This test is used to detect the adulteration of water in milk. Due to the soluble components of milk (i.e. lactose and salts), normal milk freezes slightly below the “freezing point” of pure water.  The cryoscope instrument is used to determine the freezing point of milk.  Small amounts of added water dilute the soluble components of milk causing the freezing point to move upward toward that of pure water.

Interpretations of cryoscope readings can be awkward. The first thing you need to recognize is the scale to which the cryoscope is calibrated. Cryoscopes can be calibrated to either the Hortvet scale (°H) or Centigrade (°C) scale. In most dairy laboratories, cryoscopes are calibrated to Hortvet. Normal commingled loads of milk typically have cryoscope values between -0.540 and -0.550 °H (-0517 and -0.527 °C). However, normal single herd results may vary depending on a variety of conditions including (but not limited to) herd health, season of the year, mineral content of the herd’s diet, animal breed and herd stress. Because of these factors, the concerns implicating adulteration of milk with water usually are noted at -0.525 °H (-0.503 °C). If a herd’s cryoscope results consistently show concern, an evaluation of the herd’s milk should be conducted to determine a “baseline” for that specific herd’s normal cryoscope reading.

Note: The cryoscope at Regulatory Services’ milk lab is calibrated in °H and all test results are reported in °H.

Note: Many dairy labs have infrared instruments that are primarily used to analyze milk samples for components. Some infrared instruments can also be calibrated to provide a FPD value for milk samples. These infrared FPD values are typically used for screening purposes. Samples determined to be suspect for added water using the infrared FPD values are typically confirmed with a cryoscope reading.


Petrifilm® Plate

Standard Plate Count Bacteria (SPC) with Petrifilm®
The Petrifilm® plate is an all-in-one plating system method that provides for the Standard Plate Count (SPC) of aerobic bacteria in milk. Pre-made films of agar are inoculated with 1:100 and 1:1000 dilutions of milk. The inoculated Petrifilm® is incubated for 48 hours and the bacteria colonies are counted by the analyst.


Charm SL

Antibiotic Test with Charm SL®
Detection of antibiotics or other growth inhibitors in raw milk is made possible by validated growth inhibitor assays or by rapid receptor based screening processes.  Acceptable test methods have been validated and approved by FDA are identified in PMO related documents.  The Charm SL® is approved  for the determination of antibiotics in raw cow and goat milk. The Charm SL® is a receptor assay utilizing rapid one step assay lateral flow technology. The procedure detects Beta- Lactam drugs (Amoxicillin, Ampicillin, Ceftiofor, Cephapicin, Penicillin G) at or below safe level/tolerance.


Sediment
The sediment test determines the level of particulates present in milk and is an indicator of milk production practices and cleanliness.  Sediment is determined by filtering a portion of milk by suction through a fine fiber filter.  The filter is then visually examined to determine the milligrams of sediment present per gallon.  In years past, the sediment test was quite common throughout the dairy industry.  Improvements in farm production practices and in milk quality have diminished the need for routine sediment testing in most parts of the US.

Other Tests
The milk laboratory at Regulatory Services has the capacity to perform the milk analyses identified above.  Periodically we may add new procedures.  Please feel free to contact us for milk testing inquiries not identified in this document.