DRAMIŃSKI - Milk mastitis

From the time the milk is secreted from the cow, it undergoes a series of cooling and heating steps. Milk straight from the cow is about 101 degrees F, but it is quickly cooled to 40 degrees F and is maintained at that temperature until it goes through processing steps.

Pasteurization of milk is done to kill bacterial contaminants while not substantially altering the milk characteristics.

* Heating at 74 C for 15 seconds (low pasteurization) results in killing most organisms and inactivates some enzymes, but does not otherwise alter the milk.
* Heating at 90 C for 15 seconds (high pasteurization) results in killing all vegetative microorganisms, inactivating most enzymes, but also rendering some whey proteins insoluble.
* Heating at 118 C for 20 seconds sterilizes the milk, killing all microorganisms, including spores, inactivating all enzyme activities, but also causes changes to the milk such as the browning reaction involving the proteins and sugars.
* Ultra-high temperature (UHT) pasteurization of milk at 145 C for a few seconds sterilizes milk while minimizing the chemical changes. UHT milk which is properly stored has a long shelf life, even at room temperature.

• (0)

Freezing point of milk: Freezing point of a solution depends on the number of particles in the solvent (water phase of milk), rather than the kind of particles. Water without solutes will freeze at zero degrees C. The presence of any solutes will depress freezing point below zero degrees C. The freezing point of milk depends upon the concentration of water-soluble components.

As milk is more diluted, the freezing point will raise closer to zero. The current official freezing point limit (-0.525 degrees Horvet or -0.505 degrees C; see Sherbon 1988 for discussion of Horvet vs Centigrade) was designed for whole-herd, bulk-tank samples or processed milk samples, and not for samples from individual cows or individual quarters. The value of -0.525 degrees Horvet is considered the upper limit which statistically is suppose to be a cut-off for most, but not absolutely all, samples to be considered “water-free” (that is, no added water).

Why would someone want to measure milk freezing point? Producers have been known to add water to their bulk tank to increase the volume of milk that they ship. They are paid in part on the total mass of milk that they ship to the processing plant. Obviously, those paying for the milk do not want to pay for added water and the freezing point of milk has ben used as a means of detecting these types of infractions.

However, freezing point of milk as a regulatory standard is really only valid for milk pooled form many cows (bulk tank milk). Many factors may affect freezing point of milk from individual cows. High producing cows might be expected to have higher freezing points than lower producing cows. Diet, and how and when the diet is fed relative to collecting the milk sample, also may affect freezing point from individual cows. Little work has been done in recent years to define freezing point on milk from modern high producing dairy cattle. [see Sherbon JW, Physical Properties of Milk, Chapter 8 in Wong et al, 1988]

• (0)

More properties of milk :

The density of milk (g/L) changes with temperature.
For example, the denisty of milk = 1.003073 - 0.000179t - 0.000368F + 0.00374N,
where t = temperature in degrees C; F = percent fat; and N = percent nonfat solids

Question: If you collected milk from a Jersey cow (5.5% milk fat; 15% milk solids) and stored the sample at 4 C, how would the density of that milk compare with the density of milk from you collected from a Holstein cow (3.5% milk fat; 12.2% solids) and stored at 4 C? What if your milk samples were stored at room temperature (22 C)?

Specific gravity of whole cow milk (ratio of density of milk to density of water) varies among breeds and among cows within breed. For example, mean specific gravity of Holstein milk at 20 C/20 C is 1.0330 (range 1.0268 to 1.0385) and for Ayrshire milk is 1.0317 (range 1.0231 to 1.0357), while Jersey milk also has a mean of 1.0330 (range 1.0240 to 1.0369). [see Sherbon JW, Physical Properties of Milk, Chapter 8 in Wong et al, 1988]

Viscosity is measured in poise, defined as the force in dynes per square cm required to maintain a relative velocity of 1 cm/sec between two parallel planes 1 cm apart. At 20 C, whole milk is about 20 centipoise, skim milk about 1.5 centipoise, and whey about 1.2 centipoise. [see Sherbon JW, Physical Properties of Milk, Chapter 8 in Wong et al, 1988]

• (0)

Some other physicochemical characteristics of cow milk:

* pH of normal milk is about 6.6 - 6.9 (milk of carnivores is about 6.2; human milk is about 7.0; cow colostrum as low as 6.0; milk from cows with mastitis as high as 7.5)
* osmolality is about 0.3 M (osmotic pressure ~ 700 kPa)
* ionic strength is about 0.08 molar
* water activity is about 0.993

• (0)

Physicochemical Properties of Milk:

At first , milk might seem to be a simple white liquid. But in fact, it is a complex mixture of a wide range of compounds imprortant to the neonate. The gross properties of milk include:

* Milk is an emulsion of fat globules, and
* a suspension of casein micelles (casein, calcium, phosphorous),
* all of which are suspended in an aqueous phase,
* that contains solublized lactose, whey proteins, and some minerals.
* Leukocytes in milk are part of the suspended phase.

• (0)

Milk composition receives a great deal of interest from a range of sciences, industries and applications. This is because the individual milk components can be considered from a number of perspectives, as indicated in the list below. In addition, the complex interactions of the milk components provide the basis for much of dairy chemistry or dairy food products manufacturing.

Views of milk components :

# The biochemistry of each component
# The mechanisms of synthesis of each component
# The role of each component in defining the physicochemical properties of milk
# The function of each component in the mammary gland
# The importance of each component to the nursing young
# The importance of each component in milk and milk products as foods for humans
# The factors that affect variability of milk component composition

• (0)

Sometimes can transmit what is called summer mastitis which is caused by Actinomyces pyogenes; this is gram positive and an environmental organism. It causes abscesses and purulent mastitis in dry cows and heifers. Also, Staph. aureus mastitis in heifers often occurs before calving and may be transmitted by flies.

• (0)

Calves suckling results in opening the teat canal, predisposing to IMI. Feeding calves with milk from cows that have mastitis may expose the calf (tonsils), although this is controversial; suckling may cause this type of mastitis, again this is controversial. The organisms associated with this mode of transmission are Strep. agalactiae and Staph. aureus, again these are controversial.

• (0)

This is usually cause by Coagulase negative Staphylococci or Corynebacterium bovis. These are considered minor pathogens which cause streak canal infections. Their presence may provide protection against major pathogens, however this is still controversial. Germicidal teat dips and dry cow antibiotic treat are effective control measures.

• (0)