1 / 21

Milk Hygiene

Milk Hygiene. Learning Objectives. Understand the public health aspects of milk hygiene, with an emphasis on pasteurization Learn the standards for Grade A milk Gain a general overview of the processing of milk from dairy farm to consumer. Composition of Cow Milk.

eben
Download Presentation

Milk Hygiene

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Milk Hygiene

  2. Learning Objectives • Understand the public health aspects of milk hygiene, with an emphasis on pasteurization • Learn the standards for Grade A milk • Gain a general overview of the processing of milk from dairy farm to consumer

  3. Composition of Cow Milk • Complex mixture of fats, proteins, carbohydrates, minerals, vitamins, and water • Cow milk: 13% solids (proteins, carbohydrates, fat, minerals, and vitamins) and 87% water

  4. Milk—Fresh Squeezed Daily • Grade A milk is defined and regulated by the Pasteurized Milk Ordinance. • Grade A milk is milk for liquid consumption and any milk in interstate commerce. • There is also a manufacturing grade (Grade B) milk classification—more lax. • Most cheese, butter, ice cream, and other dairy products are made from Grade A. • The PMO is revised every 2 years at the National Conference on Interstate Milk Shipments (NCIMS). • The following are represented at the NCIMS: • FDA • USDA • State & local governments • Dairy industry • Academia

  5. Hazards • Milk is not bacteriologically sterile. • Mastitis organisms • Bacteria in teat canal • Bacteria on the skin of the teat • Post- harvest contamination

  6. Pasteurized Milk Ordinance—PMO Grade A Milk leaving the farm: • Cooled to 7C (45F) within 2 hours • Somatic Cell Count <750,000/ml • Bacterial count < 100,000 ml • No positive drug residue test

  7. Causes of high bacterial counts • Milking dirty cows • Cleaning water temperature and volume • Cracked rubber parts • Dirty gaskets • Biofilm, particularly in bulk tank • Inadequate cleaning of bulk tank • Mastitis bacteria

  8. Sanitation • Sanitation starts with the premises • Milking parlor, and all equipment inside of the parlor, should be easy to clean. • Yard and pasture for cows has no standing pools of water or feces. • Appropriate bedding for resting cows. • Sanitation also applies to cows • Udder, flanks, bellies, and tails should be clean and dry. • Sanitize (teat dip) and dry teats before milking. • And to personnel (toilets, hand washing)

  9. Storage and Transport of Milk • Milk is stored on the farm in refrigerated, usually stainless steel, bulk milk tanks • Under the PMO, milk may be stored for up to 4 days in this tank. • Transport is via insulated tanker trucks • The tanker load is tested for antibiotic residues before it is unloaded. The tanker may pick up from more than one farm. • Milk receiving station • Milk is analyzed for bacteria, somatic cell counts, and composition (fat and other components).

  10. Sorting out the liquid • Clarifier = remove sediment • Milk is pumped through a centrifugal device to remove large particulate matter. • It removes dirt, straw, blood, somatic cells, and manure. • It does not remove bacteria. • Separator = separate milk with different amounts of fat • Also based upon centrifugation • Separates: skim milk, 1% milk, 2% milk, cream

  11. Pasteurization of Milk • Brief heating is used to kill common pathogens in milk; milk is not sterile. • Destroys pathogens and many of the other microbes • Inactivates enzymes in milk (e.g., lipase) • Enhances the shelf life • Pasteurization is currently based on the thermal death of Coxiella burnetii • Of all microbes found in milk, this is the most difficult pathogen to kill with heat—standards set in the 1950s. • Some debate about M. paratuberculosis—can survive some modern HTST pasteurization processes.

  12. Pasteurization: Time and Temperature • Batch pasteurization • Entire vat is heated and held at temperature for the appropriate length of time • Continuous-flow pasteurization (e.g. HTST) • Milk flows through a heated tube, with a carefully monitored transit time and temperature • Less of a cooked flavor than seen with batch methods

  13. Pasteurization • In the diagram, the homogenizer and the pasteurizer are in a sense a unit. The milk enters the pasteurizer at the heat regeneration section, where it gets heated by the hot milk emerging from the holding section. The warmed milk is now piped to the homogenizer. After homogenization, it is piped back into the pasteurizer where it enters the high heat section, that also serves as the holding section (80°C/30sec). From the holding section, the milk enters the heat regeneration side, where it is used to warm the incoming milk. Finally, it is sent through the cooling side to emerge as cold, homogenized, pasteurized milk.

  14. Standards for Grade A Pasteurized Milk:The End Product • After pasteurization • Cooled to < 45°F and maintained as such • <20,000 bacteria / mL • <10 coliform bacteria / mL • Phosphatase test must be negative • For cheese or cottage cheese—no bacterial limit, coliform < 10/ml

  15. Milk and Microbes

  16. Sources of Microbes in Milk • Udder: infections of the udder • Mastitis • Some systemic infections • Exterior of animal: dirt/mud, feces, hair, and so forth • Air: dusts, aerosol, and so forth • Milking equipment • Personnel • Water

  17. Mastitic Milk • Mastitis—inflammatory reaction of the udder • Caused by: S. aureus, Streptococcus spp., E. coli, Klebsiella, Mycoplasma spp., Serratia, and so forth • Increased blood proteins and leukocytes in milk • Decreased milk yield • In a dairy, 5–10% of cows may produce abnormal milk at any one time • Many cases are subclinical • Economic cost: $185/cow/year (1996 estimate), or 10% of the value of total milk sales for the farm

  18. Mastitis and Somatic Cell Count • Somatic cells (leukocytes) per mL of milk • Automated machine counter • Healthy milk <100,000 / mL • Mastitis cases = high SCC and low production • SCC >200,000 may be a subclinical case • Dairies with low production can have <40% of cows with subclinical mastitis • Top-producing dairies have <5% • Clinical mastitis  SCC in the millions, 30% loss in milk production per day

  19. Somatic Cell Count • 750,000 cells/mL in bulk milk tank is the legal maximum for Grade A cow’s milk in the U.S. • Most dairies in the U.S. are well below this. • Mean for U.S. ~230,000 cells/mL (2009) • Lower in winter than in summer, in the western U.S., and in large dairy herds • Only 4% of ~540,000 herd-test days had SCC >750,000 • Limits for Grade A milk are lower in the EU (400,000) and in Canada (500,000) • 17% of U.S. herd-test days were >500,000 Norman HD et al. 2000. Herd and State Means for Somatic Cell Count from Dairy Herd Improvement. J. Dairy Sci. 83:2782-2788.

  20. Sales of Unpasteurized Milk • Belief that nutrients are lost by pasteurization • Belief that pasteurization causes milk allergies“Present day milk intolerance and milk allergy is the result of denatured milk that has been heat-treated (pasteurized).” Homeopathy and Milk Intolerance, Steve Olsen, CCH • Illegal in most states • Cow shares

  21. USA Disease Outbreaks from Raw Milk

More Related