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

Milk lactose – main roles in human body

Milk is an emulsion produced by mammary glands which characterise with white colour, mild taste and flavour.

The major constituent of milk is water, but milk contains varying levels of lipids, proteins, and carbohydrates which are synthesized within with mammal gland. Their composition is influenced by animal species, environmental conditions, nutrition of animals, their lactation state and others.

Lactose is the principal carbohydrate found in milk. It is virtually unique to milk, having been found elsewhere only in fruits of certain members of the Sapotaceae. Lactose is consumed through milk and other unfermented dairy products, such as ice cream.

Disaccharides lactose in milk imparts sweet profile and human milk has a major concentration of lactose (7.4%) compared to milk of other species. The main role of lactose includes:
*It provides galactose for the synthesis of the nerve structures of the growing infant
*In the intestine, it gets metabolized to lactic acid which eliminates harmful bacteria.

Lactase is a membrane-bound enzyme located in the brush border epithelial cells of the small intestine. Once lactose reaching the small intestine, where the hydrolytic enzyme lactase (β-galactosidase) is located, lactase catalyzes the hydrolysis of lactose into its constituent monosaccharides (glucose and galactose). Only monosaccharides among the carbohydrates are absorbed from the intestines.

Lactose accounts for ~30% of the caloric value of whole milk. Lactose is an important energy source and sometimes it is referred to simply as milk sugar, as it is present in high percentages in milk. Lactose-intolerance individuals have a lactase deficiency; therefore, lactose is not completely catabolized.
Milk lactose – main roles in human body

Characteristics of lactose

Lactose biosynthesis takes place in the mammary gland. Concentrations in milk vary strongly with species. It is known as milk sugar. Lactose content of cow milk is 4.9 percent.

Lactose is a disaccharide consisting of galactose and glucose, linked by a β-L-4 glycosidic bond. Its systematic name is β-0-D-galactopyranosyl-(1–4)- α-D-glucopyranose (α-lactose) or β-0-D-galactopyranosyl-(1–4)-β-D-glucopyranose (β-lactose).

Lactose is a disaccharide, composed of two molecules of monosaccharides; glucose, and galactose. Lactose is readily fermented by the lactic acid fermenting bacteria producing lactic acid and has significance in milk and milk products.

Lactose in solid form can either be in a crystalline state or in an amorphous state. Crystalline lactose can exist in a number of distinct forms. Most well-known are α-lactose monohydrate and β-lactose. Β form is more soluble than the α form in water.

Neither α-lactose hydrate nor β-lactose is hygroscopic. However, anhydrous α-lactose is strongly hygroscopic and can absorb moisture from the air, forming the hydrate that occupies more volume than the anhydrous form.

Lactose is not digested until it reaches the small intestine, where the hydrolytic enzyme lactase is located. Lactase (β-galactosidase), which is located in brush border epithelial cells of the small intestine, catalyzes the hydrolysis of lactose into its constituent monosaccharides. Only monosaccharides among the carbohydrates are absorbed from the intestines.
Characteristics of lactose

Lactose Intolerance

Lactose intolerance is the inability to digest significant amounts of lactose, the major sugar found in milk.

Normally upon the consumption of lactose, it is hydrolyzed by the intestinal brush-border enzyme, lactase, into absorbable sugars, namely glucose and galactose. Lactase is found in the small intestine and localized to the tips of the villi, a factor of clinical importance when considering the effect of diarrheal illness on the ability to tolerate milk.

Deficiency of lactase due to primary or secondary causes results in clinical symptoms. Lactase nonpersistence results in incomplete digestion of an ingested load of lactose; hence lactose is malabsorbed and reaches the colon. If sufficient lactose enters the colon, the subject may experience symptoms of abdominal pain, bloating, excess flatulence, and diarrhea, a condition known as lactose intolerance

There are 4 main causes of lactase deficiency:

*Primary Lactase Deficiency
It is the most common cause of lactase deficiency, also known as lactose non­persistence. There is a gradual decline in lactase enzyme activity with increasing age. Most people will not notice symptoms until they are much older.

*Secondary Lactase Deficiency
Secondary Lactase Deficiency occurs when injury to intestinal mucosa due to several infectious, inflammatory or other diseases can cause secondary lactase deficiency. These diseases include celiac disease, inflammatory bowel disease, and Crohn’s disease.

*Congenital Lactase Deficiency
Some people are born with a likelihood of developing primary lactase deficiency because it has been passed to them genetically.

*Developmental Lactase Deficiency
It is seen in premature infants born at 28 to 37 weeks of gestation. The intestine of the infant is underdeveloped resulting in an inability to hydrolyze lactose.

Common symptoms, which range from mild to severe, include nausea, cramps, bloating, gas, and diarrhea. Symptoms begin about 30 minutes to 2 hours after eating or drinking foods containing lactose.
Lactose Intolerance

Sugar milk: Lactose

Disaccharides are too large to move through cell membranes, so they must be digested via hydrolysis. Disaccharides found in food include sucrose, lactose, and maltose, a grain sugar, all of these contain glucose.

Lactose is a naturally occurring carbohydrate found in the milk of most mammals. The disaccharide lactose occurs in milk, mainly free with a small extent as a component of higher oligosaccharides. Its concentration in milk varies with the mammalian source from 2.0% to 8.5%. Cow and goat milks contain 4.5–4.8% and human milk about 7%. It is the primary carbohydrate for developing mammals.

Lactose production in nature is limited to the mammalian breast, which contains the enzyme system (lactose synthase) necessary to create this linkage.

Lactose is a disaccharide consisting of galactose and glucose, linked by a β -L-4 glycosidic bond.  In milk, lactose is normally found as either α-lactose or β -lactose or amorphous glass form (mixture of α- and β -forms).

Lactose is one of the lowest ranking in terms of sweetness, being about one-sixth as sweet as sucrose.
Sugar milk: Lactose

What are the causes and symptoms of hypolactasia?

Milk is the only source of lactose, a disaccharide. Lactose is hydrolyzed to its monosaccharides, glucose and galactose, by a specific enzyme, lactase, which is β-galactosidase and located in the brush border of small-intestinal microvillus epithelial cells.

Hypolactasia is defined as lactase deficiency inherited as an autosomal recessive trait. Lactose intolerance is defined as symptomatic hypolactasia.

There are five causes of hypolactasia
*Congenital loss and it is very rare
*Inherited loss on weaning (very common)
*Gut infections such as rotavirus and Giardia
*Damage to the villi in the small intestine caused by radiotherapy or bacterial overgrowth
*Hormonal disturbances, menopause and aging

The symptoms are the result of lactose absorbing water in the intestine through osmotic mechanism, which speeds intestinal transport. Lactose is then metabolized by colonic bacteria producing lactic acid, hydrogen and CO2.

Among hypolactasia symptoms:
*Flatulence and meteorism
*Ill-defined abdominal pain
*Diarrhea

The symptoms start 1-2 hours after a lactose-containing meal and its depend on the amount of ingested lactose.

In children hypolactasia rarely develops before the age of 5 years. School-aged children often have milk-induced complaints associated with hypolactasia.

Hypolactasia occurs in 17% of Northern European inhabitants. It is more common in the Mediterranean are and much more common in many tropical countries.
What are the causes and symptoms of hypolactasia? 

Sugar and Vitamins in Milk

Sugar
Lactose is the characteristics carbohydrate of milk, is a disaccharides with the formula
C12H22O11.H2O

The chemical reaction of sugar brown shows that it does not exist in the form of a chain but has a ring structure. With glucose and galactose, the ring forms from the C1 atom to the C5 atom via an oxygen bridge. Bonding takes place between the C4 atom of glucose and C1 atom galactose. The position of the OH group on the C1 atom is in the function of direction (alpha-position for the right and Beta-position for the left direction).

Lactose has technological importance during all acidification process involving milk (acidified products, creaming ripening), in which it serves as the substrate for the lactobacillus bacteria, as well as during its direct manufacture. In addition, lactose can participate in reactions during technological process, leading to the formation of lactulose and in Maillard reactions.

Vitamin
Vitamins are formed in plants through the influence of sunlight. They are essential reagents for men and animal for maintaining and growth of cell substances as well as to guarantee the normal functioning of the organs. They function with the minutest amounts and do not provide energy.
Vitamins are transferred onto the body via food or are made out of provitamins, if the level of vitamins contained in food is too low, then deficiencies (hypo and avitaminosis) can occur, which may result in death. In a few cases, the intake of too high levels of vitamins, e.g., through supplements can lead to disturbances (e.g., hypervitaminosis).

Milk contains all the essential vitamins, but in varying and sometimes insufficient amount. The vitamin content of raw milk is influenced mainly by the feeding and health of the animal. The vitamin content can be reduced further by treatment. Milk also contains the fat soluble vitamins E (tocopherol), F and K as well as the water soluble vitamins B1 (thiamin), B12, vitamin H, pantothenic acid, folic acid and nicotinic acid amide.
Sugar and Vitamins in Milk

Lactose Intolerance

Lactose Intolerance
Many individual demonstrate a permanent loss of the enzyme used to digest the principal milk sugar lactose; they are lactose intolerant.

Lactose intolerance may be due to the absence of or insufficient amount of lactase, a birth deficit, or physical impairment.

Caucasian are among the few population groups who can digest lactose.

If lactase remains undigested by lactase in the intestine, it is fermented by microflora to short-chain fatty acids and gasses such as carbon dioxide, hydrogen, and in some individuals to methane.

Symptoms of lactose intolerance include flatulence, abdominal pain and diarrhea due to the high solute concentration of undigested lactose.

A correct understanding of tolerable dose is needed by the lactose intolerant individual and the food industry that develops lactose free food.

Lactose assists in the absorption of calcium, phosphorus, magnesium, zinc and other mineral from small intestine brush border.

Non-dairy “milk” such as soy or imitation milk contains no lactose; therefore, it may be consumed by individuals who milk allergies and by those who would otherwise not drink milk.

The loss of lactase activity in the intestine affects, to some extent, approximately 75% of the world’s population.

Individuals with lactase intolerance may compensate by consuming lactase treated milk (which reduces lactose by 70%) or purchase the lactase enzyme and administer it directly to milk prior to consumption.

It has been shown that small serving (120 ml = 6 g of lactose) of milk and hard cheeses (less than 2 g of lactose) may be consumed without an increase in intolerance symptoms.

Up to 12 g of lactose are tolerated, especially if the individual consumes other foods with the source of lactose.

Some fermented products, such as cheese, are tolerated if lactose has sufficiently been converted to lactic acid. Aged cheese is an example of such food.
Lactose Intolerance

Lactose (milk sugar)

Lactose (milk sugar)
The characteristics carbohydrate of milk is lactose, a disaccharides composed of one molecule of D-glucose and one of D-galactose, which is synthesized in the mammary gland.

The lactose content of cow’s milk is fairly constant, ranging from 4 to 5%. In contrast, milk from cows with mastitis have lactose contents as low as 2.7%.

The more lactose a milk contains, the sweeter its taste. Cow’s milk, with a mean lactose content of 4.6%, tastes faintly sweet.

It is interesting to note that although sweet (nonacid), whey has about the same concentration of lactose as the milk from which it is made, it is much sweeter than milk, due to undoubtedly to the removal of casein.

Lactose in milk is readily fermented by a number of bacteria to yield lactic acid. The changes that accompany the conversion of lactose into lactic acid is associated with the souring of milk. The odor of sour milk is not due to lactic acid but to other volatile products formed during fermentation.

Lactose, in common with other disaccharides, must be hydrolyzed by specific enzymes in the digestive tract into monosaccharide before absorption and utilization by the body.

Lactase the enzyme responsible for the hydrolysis of lactose to D-glucose and D-galactose occurs in the intestinal mucosa of mammals. When lactose intake exceeds the amount that lactose can hydrolyze, symptoms of lactose intolerance (flatulence, cramps, and diarrhea) may ensue.
Lactose (milk sugar)

Definition and Nutritional Values of Milk

Definition and Nutritional Values of Milk
Milk is the normal secretion of the mammary glands for the feeding of the young of mammals. In the United States, the primary milk in this food products rest primarily with the individual states rather than with the federal government. Consequently, legal definitions of milk are not uniform within the United States. The U.S Public Health Service has encouraged the adoption of adequate and uniform state and local control registration. The following definition from its Grade A Pasteurized Milk Ordinance (1965) has been adopted by a majority of the states.

“Milk is hereby defined to be the lacteal secretion, practically free from colostrum, obtained by the complete milking of one or more healthy cows, which contains not less than 8.25% milk solids not fat and not less than 3.25% milk fat.”

The composition of milk is rather complex. Of the major components of milk, the one that most readily distinguishes milk from other foods is lactose, which occurs naturally only in milk. Similarly, casein occurs in milk. The proteins of milk are great importance and contribute essential amino acids necessary for normal health and growth. Milk fat is a palatable mixture of glycerides of fatty acids. The components are in the complex equilibrium, and much is yet to be learned regarding the forms and combinations in which they exist. Lactose and some mineral salts are in the true solutions; the milk proteins as well as some of the calcium phosphate exist in colloidal solution; the fat exists in macroscopic dispersion in the milk plasma. Besides these major constituent, milk contains other constituents such as vitamin, enzymes, pigments and lactic acid.
Definition and Nutritional Values of Milk

Nutrients in Milk

Nutrients in Milk 

Lactose It is the principal and typical carbohydrate of milk, known as milk sugar. Glucose, galactose and other sugars such as oligosaccharides are also present in traces. Lactose exists in true solution in milk. It is a disaccharide, composed of two molecules of monosaccharides; glucose, and galactose. Lactose is readily fermented by the lactic acid fermenting bacteria producing lactic acid and has significance in milk and milk products. It exists in two isomeric forms, designated as α and β forms of which the β form is more soluble than the alpha form in water. Lactose content of cow milk is 4.9 percent. The lactose content of milk is inversely proportional to the ash content of the milk. Udder infection promotes an increased level of chloride in the milk and depresses the secretion of lactose.

Proteins Milk protein is a rich source of essential amino acids. Whey proteins are proteins that are passed along with the whey portion after the coagulation of milk. They contain 51% essential amino acids when compared to 45% in casein. The sulphur containing amino acids, which are considered essential and important, are found in higher concentration in whey protein than in casein. Usually the quality of egg proteins are regarded as very high. But the net protein utilization, biological value and the protein efficiency ratio of milk protein come neck in neck with the quality of egg protein. Lactalbumin, a whey protein , whose biological value, net protein utilization and protein efficiency ratio is considered superior when compared to the major milk protein, casein. Normally double the quantum of vegetable protein is required to meet the daily requirement of essential amino acids when compared to that obtained from the milk proteins.

Casein May be defined as the major protein, which is precipitated at pH 4.6 and is exclusive to milk. It is present in spherical bodies as micelles, which vary in size with negative surface charge. The caseins of milk may be sub-divided into five main classes, αs1, αs2, β, gamma and k-caseins. In milk, casein is present in combination with calcium in the form of calcium caseinate or more precisely calcium hydrogen caseinate.

Whey proteins Are those in the whey fraction, after the precipitation of casein at pH 4.6. These are the alpha-lactalbumin, beta-lactoglobulin, immunoglobulins, lactoferrin, transferrin, proteose-peptone fractions etc. Most of these are globular proteins subject to heat denaturation. α-lactalbumin exists in variants A and B forms and is susceptible to denaturation by unfolding of the tertiary structure. β-lactoglobulin is identical to blood globulin and insoluble in water and is responsible for the transfer of antibodies. Normal milk contains 0.1%, whereas colostrum contains 6 %.

Milk fat The digestibility of milk is comparatively higher than other oils and fats. This can be attributed to existence of fat globules in aqueous phase forming an emulsion. This facilitates its easy absorption through the intestinal tract when compared to other fats which have to be emulsified with bile salts, enzymes from pancreas and fat splitting lipases. Endowed with short and medium chain fatty acids, milk fat can be easily absorbed when compared to long chain fatty acids because of the ability of the lipases to split the ester bonds in the former. Supplementation of milk fat in the diet increases the energy density. When compared to human milk, the cow milk is low in essential fatty acids such as linoleic and linolenic acids. Short and medium chain fatty acids with 4-12 carbon atoms, which occur at comparatively higher concentration in milk fat, reported to have antibacterial and fungistatic activity. Milk fat plays another important role in preventing tooth decay by forming a protective coat over the surface of enamel. It is composed of triglycerides of fatty acids. A fatty acid molecule is composed of hydrocarbon chain and carboxyl group. Triglycerides are of two types, simple and complex. In simple, all the three fatty acids are of same nature, whereas complex triglycerides on hydrolysis give glycerol and different fatty acids. The milk fat exists in the form of small globules of sizes ranging from 2 to 10 microns with different glycerides of low melting points in suspension. Milk fat varies in amount and composition, according to the breed, species, feed and lactation time, of which, feed being a major factor. Fat is distributed in globules as triglycerides (98-99 %), fat globule membrane in combination with phospholipids and lipoprotein (0.2 to 1.0 %) and also as free fatty acids, cholesterol and phospholipids in the serum.

Phospholipids These contain phosphorus in their molecules in addition to the fatty acids and glycerol; they also contain a nitrogenous base. Principally milk phospholipids are the Lecithin, Cephalin and Sphingomyelin. Though fat-soluble, they are hydrophilic and imbibe large quantity of water and swell. They are used as antioxidants for fat rich dairy products.

Vitamins Various vitamins present in milk are as follows. Fat Soluble Vitamins - include vitamins A, D, E and K. Water-soluble vitamins are the, B1 (thiamine), B2 (riboflavin), B6 (pyridoxine), Biotin, Niacin (nicotinic acid), Pantothenic Acid, Para-amino benzoic acid, Inositol, Choline, Folic acid, B12, and Ascorbic acid. Fat rich milk products contain large quantities of fat soluble vitamins, whereas whole milk, skim milk, buttermilk and whey are a good source of water soluble vitamins.

Minerals The portion left after ashing of milk at 150ºC is known as the 'ash of milk' and is composed of various inorganic constituents. Ash forms about 0.75 % of milk and plays a very important role in milk and is basic in character. The minerals in milk consist principally of the chlorides, citrates and bicarbonates of calcium, magnesium, potassium and sodium.

Nutrients in Milk Article Source: http://EzineArticles.com By Thenmozhi Kathirvelu