Milk Sampling

Milk sampling is a critical process in assessing and ensuring milk quality, whether for safety, composition, or regulatory compliance. It involves collecting representative portions of milk at various stages—farm, transport, or processing—to analyze for microbial content, chemical composition, contaminants, and physical properties. Here’s a detailed overview of milk sampling, including methods, purposes, and best practices:

Purposes of Milk Sampling

1. Quality Control:

   • Monitor microbial load (e.g., total bacterial count, pathogens).

   • Check somatic cell count (SCC) for cow health.

   • Assess fat, protein, and lactose levels for nutritional and payment purposes.

2. Safety Assurance:

   • Detect contaminants like antibiotics, aflatoxins, or pesticides.

   • Ensure compliance with food safety standards (e.g., FDA, EU regulations).

3. Process Optimization:

   • Evaluate milk suitability for products like cheese or yogurt.

   • Identify spoilage or flavor defects early.

4. Regulatory Compliance:

   • Meet standards for raw or pasteurized milk (e.g., Grade A requirements).

Sampling Points

• Farm Level: From individual cows, bulk tanks, or milking parlors.

• Transport: During collection from farms or delivery to processors.

• Processing Plant: Raw milk intake, post-pasteurization, or final product.

Sampling Methods

1. Manual Sampling:

   • Tools: Sterile dippers, pipettes, or ladles.

   • Process: Collect from well-mixed milk (e.g., after agitation in a bulk tank) to ensure uniformity.

   • Use Case: Common on small farms or for spot checks.

2. Automatic Sampling:

   • Tools: In-line samplers integrated into milking machines or pipelines.

   • Process: Continuously or periodically draws small amounts during milking or transfer.

   • Use Case: Large-scale operations for consistent, representative samples.

3. Composite Sampling:

   • Process: Combine samples from multiple milkings or cows over a period (e.g., a day or week).

   • Use Case: Assess average quality for payment or herd health monitoring.

4. Spot Sampling:

   • Process: Take a single sample at a specific time or from a specific cow.

   • Use Case: Diagnose issues (e.g., mastitis in an individual cow).

Best Practices for Milk Sampling

1. Representative Sampling:

   • Agitate milk thoroughly (e.g., 5-10 minutes in a bulk tank) to mix fat and solids, as they separate naturally.

   • Avoid sampling from the top (fat-rich) or bottom (sediment) without mixing.

2. Sterility:

   • Use sterile containers (e.g., plastic vials, glass bottles) and tools to prevent contamination.

   • Clean and sanitize sampling equipment between uses.

3. Timing:

   • Sample raw milk soon after milking, before significant bacterial growth.

   • For transport or processing, sample at key transition points (e.g., tanker loading).

4. Temperature Control:

   • Keep samples cold (0-4°C/32-39°F) immediately after collection to halt microbial activity.

   • Use ice packs or refrigerated transport; avoid freezing unless specified (e.g., for some compositional tests).

5. Labeling:

   • Record date, time, source (e.g., cow ID, tank number), and purpose to ensure traceability.

6. Volume:

   • Collect enough for analysis (e.g., 50-100 mL for microbial tests, 250 mL for composition), per lab requirements.

Common Analyses Performed on Samples

• Microbial: Total plate count, coliform count, pathogen screening (e.g., Listeria, Salmonella).

• Somatic Cell Count: Via flow cytometry or microscopy.

• Composition: Infrared spectroscopy for fat, protein, lactose.

• Contaminants: Chromatography (e.g., HPLC) for antibiotics, ELISA for aflatoxins.

• Physical: Freezing point, pH, titratable acidity.

Challenges in Milk Sampling

• Non-Uniformity: Fat separation or sediment can skew results if not mixed properly.

• Contamination: Poor hygiene introduces false positives in microbial tests.

• Degradation: Delays or improper cooling alter bacterial counts or composition.

• Variability: Milk from different cows, times, or seasons may differ, requiring careful sampling strategies.

Standards and Guidelines

• U.S.: The Pasteurized Milk Ordinance (PMO) outlines sampling protocols for Grade A milk, emphasizing frequency (e.g., monthly farm samples) and handling.

• EU: Regulation (EC) No 853/2004 specifies raw milk sampling for bacterial and SCC limits.

• IDF/ISO: International Dairy Federation and ISO standards (e.g., ISO 707) provide detailed methods for sampling and analysis.

Practical Example

• Farm Bulk Tank:

  1. Agitate tank for 5 minutes.

  2. Use a sterile dipper to collect 100 mL from the middle of the tank.

  3. Transfer to a sterile bottle, seal, and cool to 4°C.

  4. Label with farm ID, date, and time; send to lab within 24 hours.

• Result: Tests might show TBC <50,000 CFU/mL and SCC <200,000 cells/mL, indicating high quality.

IMPORTANT POINTS TO BE KEPT IN MIND WHILE SAMPLING MILK 

1. Make sure that all the glassware’s, equipments and instruments are cleaned, sterilized and dry.

2. Label sample bottles/tubes prior to sampling (temperature, date, farm, cow, quarter etc). 

3. Sampling of milk should be done at 90°F to 104 °F (about 32°C to 40°C). 

4. If you have to transport the milk over long distances, chill and transport it using insulated containers/refrigerated trucks.

5. Ensure that you examine the samples as soon as you draw them since chemical and microbiological changes may affect the results obtained.

6. Avoid violent mixing of the milk since the viscosity of milk will not allow air bubbles to rise to the top. The fat globules will also take place.

7. Unfreeze (thaw) milk (in case of frozen milk) before sampling begins.     

8. Ensure you have a uniform mix of the milk from which you intend to draw the sample.

9. Fat is the most variable constituent of a standing milk sample therefore do not allow the milk to stand for longer than five minutes after mixing and take required quantity of milk with the help of a dipper. 

10. You should only used chemically preserved milk for a chemical analysis. 

Depending upon the type of container used for milk transportation, there may be some variations in methodology followed for sampling of milk. Usually sampling of fresh milk consists of the following:

1. Sampling of milk from pail/bucket:

Most effective way of mixing is pouring the milk from one pail to another atleast three times and then immidiatly withdraw the milk sample.

2. Sampling of milk from individual animal (directly): Wash the flak area with warm water. Dry the udder and its teats and its orifice with a piece of cotton soaked in 70% ethyl alcohol. Take the milk sample from each quarter separately. This way of collecting sample is of paramount importance for microbiological analysis specifically for identification of mastitis pathogens. Aseptic technique is an absolute necessity when collecting milk samples to prevent contamination by organisms found on the cows' skin, udder, and teats; hands of the sampler; and in the barn environment.

3. Sampling of milk from the herd ( several animals): Collect samples from each animal as above, mix appropriate proportion of all samples together by plunger for 30 seconds then take the universal sample.

4. Sampling of milk from single can: Take sample with the help of dipper after well mixing the milk by plunger. 

5. Sampling of milk from several cans: Take samples from each can as above and take universal sample after mixing appropriate proportion of all samples together.

6. Sampling of milk from bulk tanker: Milk should be agitated for at least 5 minutes prior to sampling. Usually mechanical agitators are used for big milk tankers for homogenous mixing before obtaining sample.