Milk

Physical properties of milk

• Appearance

  The opacity of milk is due to its content suspending particles of fat, protein and certain minerals. Milk color varies from white to yellow according to the carotene content of fat. Homogenization increase in the number and total volume of fat globules this results in white color of the homogenized product.

•  Flavor

  The flavor of milk is a property difficult to define but there is no doubt that taste and aroma are critical to the assessment of milk. Milk flavor constitutes critical criteria of judging its quality by the consumer. It is a sensory property in which odor and taste interact. The sweet taste of lactose yeast balanced by the salty taste of chloride and both are some what moderated by proteins. Saltiness can be detected by sensory test. In sample contain 0.12% or more chloride iron and it become mark in samples containing 0.155 chloride iron. Milk has a clean pleasant sweet flavor but any off flavor can be readily identify off flavor development, when the balance of flavor compounds are described due to the microbiological activity or processing treatments or chemical or biochemical reaction during milk production processing and storage.

• Acidity and pH

  The pH of normal fresh sweet milk usually varies from 6.6-6.8, buffalo milk have slightly high pH than cow milk indicate udder infection- mastitis and lower values bacterial action. The acidity of milk is the titratable acidity which measure the amount of alkali required to change pH of milk from 6.8 to pH of color change of phenolphthalein is added and pH is 8.3. The normal range of acidity of milk is varies from 0.1-0.17% lactic acid any value is excess of 0.175 can regarded as developed lactic acid.

• Density and Specific Gravity

  The density of milk with 3-5% fat averages 1.032gm per centimeter cube accordingly the weight of 1 liter of milk is 1.032kg. The specific gravity of milk is the ratio of density of milk to that of water at the same temperature. The specific gravity lies in the range 1.030-1.035 with an average of 1.032, the specific gravity of milk fat is 0.93, SNF 1.614, skim milk 1.036 and whole milk 1.066.

The percentage of total solid or SNF in milk is calculated using the formula

Total solid %= 0.25D+0.22F+0.72

 Where

            D= 1000*(d-1)
            d= density of sample of milk at 20C
            F= fat percentage of sample

• Freezing point

  Milk freezes at a temperature slightly lower than water due to the presence of solute constituents such as lactose, soluble salts etc. The average freezing point of cow milk is -0.547C and buffalo milk is -0.549C. The freezing point of milk is used for detecting water adulteration, addition of water increase the freezing point.

• Boiling Point

  The milk constituent in the solution is responsible for the elevation of the boiling above 100C. The boiling point of buffalo milk is 100.55C and cow milk is 100.17C