The Role and Properties of Lactose in Milk and Dairy Products

Lactose, commonly referred to as milk sugar, is the primary carbohydrate found in milk. As a disaccharide, lactose consists of two monosaccharides: glucose and galactose. This milk sugar is found in a true solution within milk, making it easily accessible for various biochemical processes. Besides lactose, milk also contains trace amounts of other sugars like glucose, galactose, and oligosaccharides.

Lactose plays a crucial role in dairy products due to its ability to be fermented by lactic acid bacteria, which convert it into lactic acid. This fermentation process is essential for the production of yogurt, cheese, and other fermented dairy products, as it influences texture, flavor, and preservation.

Lactose exists in two isomeric forms: α-lactose and β-lactose. The β-lactose form is more soluble in water than the α-lactose form, affecting the solubility and crystallization of lactose in dairy products. In cow's milk, lactose makes up approximately 4.9% of the milk's composition. Interestingly, the lactose content of milk is inversely related to its ash content, meaning higher ash content correlates with lower lactose levels.

Furthermore, udder infections can significantly impact milk composition. Such infections often lead to increased chloride levels in milk and a reduction in lactose secretion, highlighting the sensitivity of lactose production to the cow's health. Understanding these dynamics is crucial for dairy production and quality control.
The Role and Properties of Lactose in Milk and Dairy Products

Goat cheese

The cheese market has expanded, and strong cheese prices have resulted in an increase in dairy goat milk and cheese production in North America as well as in many other developed countries.

Goat cheese was originated in Mesopotamia. The milk was probably made into soft cheese and then hard, ripened goat cheeses were later developed in the Mediterranean Basin countries.

Goat cheese has a very tangy flavor, and it is most commonly found as a soft, yet crumbly cheese though firm, aged goat cheeses are available as well. Fresh goat cheese is a healthier option than cow’s milk cheese, due to the lower fat content.

The general procedures of cheese manufacturing are:
*Standardizing the milk
*Setting the temperature
*Adding starter cultures
*Adding rennet
*Cutting curds
*Cooking
*Draining whey
*Salting
*Hooping *Pressing
*Packaging
*Aging

Goat cheese should be sliced using un-waxed dental floss. Cross the ends of the string above the cheese and pull the string through the cheese to make slices.
Goat cheese

Chemical properties of milk

The processability and functionality of milk and milk products are determined by the properties and concentrations of its principal constituents: protein, lipids, lactose and salts.

Milk fat occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey). Milk fat is composed of approximately 400 fatty acids.

The fat globules (called cream) separate after prolonged storage or after centrifugation. The fat globules float on the skim milk.

Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not occur even after prolonged standing. The key attributes of milk flavor are influenced by its emulsion of fat globules in a colloidal protein solution, accompanied by a slight sweet and salty taste from lactose and minerals, primarily calcium.

The majority of milk proteins are synthesized from amino acids. Proteins of various sizes are dispersed in milk serum. They are called micelles and consist mostly of calcium slats of casein molecules.

Furthermore, milk contains lipoprotein particles, also called milk microsomes, which consist of the residues of cell membranes, microvilli, etc., as well as somatic cells, which are mainly leucocytes.

Various proteins, carbohydrate, minerals and other ingredients are solubilized in milk serum.

Milk contains many acidic and basic groups that result in buffering action over a wide pH range. The principal buffer components in milk are soluble phosphate, colloidal calcium phosphate, citrate, bicarbonate and casein.
Chemical properties of milk

Milk

The Holstein breed outnumbers all others used in the United States for the production of milk.

Jersey and Guernsey breeds tolerate hot weather better than Holsteins, hence may be the predominant types used for the production of milk in hot weather in certain areas.

Cow’s milk contains an average of 3.8% fat (called butter fat), 3.3% protein, 4.8% lactose (a 12-carbon sugar), 0.7% ash (minerals), and 87.4% water.

Milk also contains vitamin and other nutrients in small amounts, making it the most complete of foods.

The young of mammalians survive on it exclusively. However, components of milk from different species vary, and occasionally the young one species may be unable to tolerate the milk from other species, mainly because of differences in lactose contained therein.

The fat content of milk from Ayrshire and Brown Swiss, and especially form Guernsey and Jersey breed, is slightly higher than that form Holstein cow’s, but later breed generally produces much more milk than the others.

Most milk is produced on farms than deal primarily with the raising of dairy cattle.
Milk

Sensory properties of milk

The sensory properties of milk and milk products are a consequence of composition, which may be manifested in ways that relate to notions of quality.

Milk sensory properties of appearance texture and flavour are largely determined by the fat concentration on the product.

Fat molecules are too large to stimulate taste or smell, but do produce tactile sensations.

Many of the compounds identified as contributing to the flavour and aroma of milk are derived from the fat and the milk fat globule membrane.

The chemical and physical properties of milk products are influenced by raw milk quality, manufacturing processes, storage condition and associated process controls.

The bland mouth-feel if milk is a consequence of the emulsion structure, while the slightly sweet and salty taste results from the balance between lactose and milk minerals.

The whiteness of liquid milk is caused by the light scattering of milk-fat globules, colloidal caseinate and colloidal calcium phosphate though the presence of carotenes is importance to the yellow color of milk-fat.

Whole milks are whiter and more viscous that’s skimmed milk. Also, the flavour of whole milk is more intense due to the naturally occurring fat flavour compounds.
Sensory properties of milk

Physical and Chemical Properties of Milk

Physical and Chemical Properties of Milk
Milk is a white or yellow-white, opaque liquid. The color is influenced by scattering and absorption of light by milk globules and protein micelles.

Therefore, skim milk also retains its white color. A yellowish, i.e. yellow –green, color is derived from carotene (ingested primarily during pasture grazing) present in that fat phase and from riboflavin present in the aqueous phase.

Milk tastes mildly sweet, while its odor and flavor are normally quite faint.

Milk occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey).

The fat globules (called cream) separate after prolonged storage or after centrifugation.

The fat globules float on the skim milk. Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not not occur even after prolonged standing.

Proteins of various sizes are dispersed in milk serum. They are called micelles and consists mostly of calcium salts of casein molecules.

Furthermore, milk contains lipoprotein particles, also called milk microsomes, which consists of the residue of cell membranes, microvilli, etc, as well as somatic cells which are mainly leucocytes.

Various proteins, carbohydrates, minerals and other ingredients are solubilized in milk serum. The specific density of milk decreases with the increasing fat content, and increases with increasing amounts of protein, milk sugar and salts.

The specific density of cow’s milk ranges from 1.029 to 1.039 (15 degree C). Defatted (skim) milk has a higher specific density than whole milk.
Physical and Chemical Properties of Milk

Physical and Properties of Milk

Physical and Properties of Milk
Milk is a white or yellow, opaque liquid. The color is influenced by scattering and absorption of light by milk fat globules and protein micelles.

Therefore, skim milk also retains its white color.

A yellowish, i.e., yellow-green, color is derived from carotene (ingested primarily during pasture grazing) present in the fat phase and from riboflavin present in the aqueous phase.

Milk tastes mildly sweet, while its odor and flavor are normally quite faint.

Milk fat occurs in the form of droplets or globules, surrounded by a membrane and emulsified in milk serum (also called whey).

The fat globules (called cream) separate after prolonged storage or after centrifugation. The fat globules float on the skim milk.

Homogenization of milk so finely divides and emulsifies the fat globules that cream separation does not occur even after prolonged standing.

Proteins of various sizes are dispersed in milk serum. They are called micelles and consist mostly of calcium slats of casein molecules.

Furthermore, milk contains lipoprotein particles, also called milk microsomes, which consist of the residues of cell membranes, microvilli, etc., as well as somatic cells, which are mainly leucocytes.

Various proteins, carbohydrate, minerals and other ingredients are solubilized in milk serum.

The specific density of milk decreases with increasing fat content, and increases with increasing amounts of protein, milk sugar and salts.

The specific density of cow’s milk ranges from 1.029 to 1.039 (15 degree C).

Defatted (skim) milk has a higher specific density than whole milk.

The freezing point of milk is -0.53 to -0.55 degree C. This rather constant value is a suitable test for detection of watering of milk.
Physical and Properties of Milk