Galactose: properties, functions in the body, benefits and harms

What is galactose?

As mentioned above, galactose is a monosaccharide of the hexose class, an isomer of glucose. It is contained in the disaccharide lactose, the substance can also be found in other polysaccharides. Although it is not an essential compound for humans, it still has an impact on the health and development of the body. Visually, the substance is a crystalline powder that dissolves in water at room temperature and is insoluble in an alcoholic environment.

Galactose can be found in large quantities in beets and some types of energy drinks. In addition, the substance is present in complex carbohydrates, which can be found in many fruits and vegetables: tomatoes, potatoes, celery, beets, kiwi and cherries. In the human body, the substance is present in brain tissue and many nerve tissues.

Galactose plays the role of a building protein, which a person receives from milk. The substance is especially important for young mothers who are breastfeeding.

In its chemical composition, galactose is close to glucose. The differences lie only in the atomic structure of the substances. Galactose can be found in many microorganisms and in almost all products of plant and animal origin. Its greatest amount is contained in lactose, that is, in dairy products.

There are two main types of galactose: L and D. The first is represented by a proportion of polysaccharides, a particularly large amount of which is found in red algae. The second is much more common - it can be found in many substances: glycosides, oligosaccharides, bacterial and plant polysaccharides, pectin substances and gums. During the oxidation process, the substance forms galacturonic and galactonic acids.

Galactose is most widespread in the medical field - it is used during ultrasound.

Genetic D-series of sugars

The founder of aldoses is glyceraldehyde. Let's consider the genetic relationship of D-series sugars with D-glyceraldehyde.

In organic chemistry, there is a method of increasing the carbon chain of monosaccharides by sequentially introducing a group

between a carbonyl group and an adjacent carbon atom. The introduction of this group into the D-glyceraldehyde molecule leads to two diastereomeric tetroses - D-erythrose and D-threose. This is explained by the fact that a new carbon atom introduced into the monosaccharide chain becomes asymmetric. For the same reason, each resulting tetrose, and then pentose, when one more carbon atom is introduced into their molecule, also gives two diastereomeric sugars. Diastereomers are stereoisomers that differ in the configuration of one or more asymmetric carbon atoms.

This is how the D-series of sugars was obtained from D-glyceraldehyde. As can be seen, all members of the above series, being obtained from D-glyceraldehyde, retained its asymmetric carbon atom. This is the last asymmetric carbon atom in the chain of carbon atoms of the presented monosaccharides.

Each aldose of the D-series corresponds to a stereoisomer of the L-series, the molecules of which are related to each other as an object and an incompatible mirror image. Such stereoisomers are called enantiomers.

It should be noted in conclusion that the given series of aldohexoses is not limited to the four depicted. In the manner presented above, two more pairs of diastereomeric sugars can be obtained from D-ribose and D-xylose. However, we focused only on aldohexoses, which are most widespread in nature.”

Galactose formula and its properties

The chemical formula of galactose is as follows:

C6H12O6

The substance belongs to the class of aldohexoses, that is, it is a polyhydroxyaldehyde. The molecule of the compound in question can be either cyclic or linear, and also exist in two different stereoisomeric forms: be an L-isomer or a D-isomer.

The D-isomer is most often found in nature as a component of oligosaccharides, glycosides and polysaccharides. The L-isomer is less common - it is a component of some types of polysaccharides and is also present in red algae.

The cyclic variety of galactose is represented by 4 isomers: two of them with a pyranose ring, and the remaining two with a furanose ring. Each cyclic form of a substance includes two anomers in its structure: the a-form and the b-form. In the case of galactose, they are spatial isomers, differing in the position of the hemiacetal hydroxyl relative to the plane of the ring.

Externally, galactose is a finely crystalline white powder with a pleasant sweet taste and odorless. The substance dissolves perfectly in ordinary water at room temperature. Thus, its solubility in water is 9.1 g per 100 g of water at a temperature of 0 degrees, and 40 g of galactose per 100 g of water at a liquid temperature of 25 degrees.

The powder melts at a temperature of 167 degrees. Galactose has a low glycemic index. The lower this indicator, the slower the blood sugar level changes.

In the human body, galactose serves as one of the main sources of energy. Once in the gastrointestinal tract as part of food, it turns into glucose, after which it undergoes the process of absorption.

Monosaccharide metabolism

Metabolism of galactose through glycolysis requires a continuous supply of UDP-glucose (the active form of glucose). Galactose is metabolized from milk sugar and, as a result of stepwise glycolysis, is converted into glucose-1-phosphate.

Most of the monosaccharide absorbed by the body goes to the liver, where it is converted into glucose, which is then used as a source of energy or converted into glycogen. Compared to glucose, galactose does not significantly increase blood sugar levels.

Functions of galactose in the body - what is it for?

For humans, galactose serves as an energy source. After entering the body, the substance is transformed into glucose and then absorbed.

Galactose is an extremely important component of food for newborns. It is part of the disaccharide lactose, which is the main carbohydrate in milk.

The result of the interaction of galactose with lipids is glycolipids, including those molecules that take part in the formation of blood group. When galactose combines with proteins, glycoproteins are formed, which play an important role in the formation of cell membranes.

In the human body, galactose performs the following functions:

• prevents the emergence and development of diseases of the nervous system;
• stabilizes the functioning of the gastrointestinal tract;
• participates in the formation of cell membranes;
• has a positive effect on the central nervous system;
• supports and stabilizes cell structure.

Galactose plays an important role in the production of lactose. In mammals, the mammary glands after pregnancy produce a large volume of lactose, which is necessary to provide nutrition to the young.

This process in women is controlled by a list of hormones that the body produces during gestation and after birth. UDP-galactose and glucose take part in the reactions. The two sugars mentioned above are combined with each other under the influence of the enzyme lactose synthetase.

Fructose and galactose

The absorption of fructose in the human body is carried out by transforming it into glucose. First, it is phosphorylated in the obligatory presence of ketohexokinase, followed by the formation of fructose phosphate, which is cleaved by aldolase to glyceraldehyde and dihydroxyacetone-3-phosphate. The latter is an intermediate product of glucose oxidation.

In the next step, glyceraldehyde is partially reduced to glycerol or oxidized to glycerate.

The process of breakdown and assimilation of fructose and galactose includes ways of using them for the synthesis of other compounds - heteropolysaccharides, lactose and other substances. Both galactose and fructose take an active part in supplying the body with sufficient energy. Fructose in this case is transformed into galactose: the process takes place in the liver - there galactose is transformed either into glucose or into intermediate products. So, as a result, fructose and galactose, just like glucose, are oxidized to carbon dioxide and water. They can also be used for the synthesis of glycogen and triacylglyderols.

The reason for the disruption of the absorption process of both substances may be the lack of enzymes necessary for this. Such disorders are quite rare, but can pose a serious danger to the human body, since the accumulated intermediate metabolites can be quite toxic.

Carbohydrates. Genetic D-series of sugars

“Carbohydrates are widespread in nature and perform various important functions in living organisms. They supply energy for biological processes and are also the starting material for the synthesis of other intermediate or final metabolites in the body. Carbohydrates have the general formula Cn(H2O)m, which is where the name of these natural compounds comes from.

Carbohydrates are divided into simple sugars or monosaccharides and polymers of these simple sugars or polysaccharides. Among the polysaccharides, a group of oligosaccharides containing from 2 to 10 monosaccharide residues per molecule should be distinguished. These include, in particular, disaccharides.

Monosaccharides are heterofunctional compounds. Their molecules simultaneously contain both carbonyl (aldehyde or ketone) and several hydroxyl groups, i.e. monosaccharides are polyhydroxycarbonyl compounds - polyhydroxyaldehydes and polyhydroxyketones. Depending on this, monosaccharides are divided into aldoses (the monosaccharide contains an aldehyde group) and ketoses (contains a keto group). For example, glucose is an aldose, and fructose is a ketose.

(glucose (aldose)) (fructose (ketose))

Depending on the number of carbon atoms in the molecule, the monosaccharide is called tetrose, pentose, hexose, etc. If we combine the last two types of classification, then glucose is aldohexose, and fructose is ketohexose. Most naturally occurring monosaccharides are pentoses and hexoses.

Monosaccharides are depicted in the form of Fischer projection formulas, i.e. in the form of a projection of the tetrahedral model of carbon atoms onto the drawing plane. The carbon chain in them is written vertically. In aldoses, an aldehyde group is placed at the top; in ketoses, a primary alcohol group is placed adjacent to the carbonyl group. The hydrogen atom and the hydroxyl group at the asymmetric carbon atom are placed on a horizontal line. The asymmetric carbon atom is located in the resulting crosshair of two straight lines and is not indicated by a symbol. The numbering of the carbon chain begins with the groups located at the top. (Let's define an asymmetric carbon atom: it is a carbon atom bonded to four different atoms or groups.)

Establishing an absolute configuration, i.e. the true spatial arrangement of substituents on an asymmetric carbon atom is a very labor-intensive task, and until some time it was even an impossible task. It is possible to characterize connections by comparing their configurations with those of reference connections, i.e. determine relative configurations.

The relative configuration of monosaccharides is determined by the configuration standard - glyceraldehyde, to which at the end of the last century certain configurations, designated as D- and L-glyceraldehydes, were arbitrarily assigned. The configuration of the asymmetric carbon atom of the monosaccharide farthest from the carbonyl group is compared with the configuration of their asymmetric carbon atoms. In pentoses, this atom is the fourth carbon atom (C4), in hexoses it is the fifth (C5), i.e. penultimate in a chain of carbon atoms. If the configuration of these carbon atoms coincides with the configuration of D-glyceraldehyde, the monosaccharide is classified as a D-series. And, conversely, if it matches the configuration of L-glyceraldehyde, the monosaccharide is considered to belong to the L-series. The symbol D means that the hydroxyl group at the corresponding asymmetric carbon atom in the Fischer projection is located to the right of the vertical line, and the symbol L means that the hydroxyl group is located to the left.

Beneficial properties of galactose

Galactose takes an active part in the creation of cell walls; it is also responsible for tissue elasticity. In addition, the substance in question is part of the lipids of the brain, blood and connective tissues.

Galactose is essential for proper functioning of the brain and nervous system. A normalized level of galactose prevents the development of senile dementia and also avoids nervous disorders. The substance helps prevent the onset and development of Alzheimer's disease.

The compound has a positive effect on the condition of the gastrointestinal tract. In addition, it takes part in the synthesis of hemicellulose, which is very important for cell development.

Galactose helps prevent the occurrence of nervous disorders.

Galactosemia

Galactosemia is a disease that is inherited. With this disorder, the organs of the digestive system stop producing enzymes that are necessary for processing galactose.

Galactosemia is most dangerous for infants. If such a diagnosis was made to the baby in the first days of life, breast milk is contraindicated for him - it will lead to serious consequences for the child.

It is worth noting that the baby also cannot be fed with cow's milk; goat's milk and adapted milk formula are also not suitable. Any milk can bring not just a deterioration in well-being, but a real mortal danger. This is due to the fact that galactose, accumulating in the blood, gradually begins to poison the body. It causes health problems: the nervous system is the first to suffer; liver cells and visual organs also experience negative consequences.

But everything is not as bad as it might seem at first glance: there is a high probability that the baby will outgrow his existing health problems. The likelihood of such healing is especially high if the level of galactose in the blood was slightly exceeded.

Why does galactosemia occur?

It has been established that the gene responsible for the production of the enzyme that breaks down galactose is inherited in a recessive manner. This means that one in 4 children of a gene parent will be diagnosed with galactosemia.

Early diagnosis and adherence to a strict diet that limits the amount of lactose consumed are extremely important - they will help prevent the child from developing mental retardation, liver failure and even death. There are two types of the disease: classic galactosemia and clinical galactosemia - both of them can lead to unpleasant consequences for the child.

In adults, galactosemia can occur due to disturbances in the GALT gene - this leads to a deficiency of the enzyme galactose-1-phosphate uridyltransferase. The enzyme is extremely important for the proper breakdown of milk sugar. Its deficiency leads to the accumulation of toxic products in the body.

Symptoms of galactosemia

The main symptom of galactosemia is decreased appetite, which can result in anorexia. An invariable companion of galactosemia is vomiting. Yellowing of the skin, changes in the color of the mucous membranes and whites of the eyes, an increase in the size of the liver, an increase in amino acids and protein in the urine, and fluid accumulation and swelling in the abdominal cavity may also occur. In advanced cases, depletion of body tissues and severe weight loss occur.

To avoid the consequences described above, it is important to follow a diet that excludes lactose from the diet.

Children with galactosemia who are not treated early may experience delayed physical and mental development. They are especially susceptible to cataracts. In advanced cases, any infection (especially in infancy) can lead to life-threatening complications. In mild cases, when receiving the necessary medical care, serious violations are not observed.

In order to avoid the consequences of galactosemia, including liver failure and kidney dysfunction, brain damage, cataracts and other ailments, it is important to promptly eliminate lactose from the diet. Patients on a special diet usually demonstrate better general health. Children with galactosemia who do not eat dairy may make greater intellectual progress and are less likely to have speech and learning problems and some behavioral problems. Girls with classic galactosemia often experience disturbances in the functioning of the ovaries - this is associated with an increase in the level of the hormone gonadotropin.

All of the above complications accompany exclusively classical galactosemia. They were not found in patients suffering from Duarte galactosemia. They also do not need to follow a strict diet.

Population groups susceptible to galactosemia

The classic form of the disease is diagnosed in a range from 1 case in 16,000 to 1 case in 48,000 births. Galactosemia is common among representatives of all ethnic groups. The disease is especially common among the Irish. But the clinical variant of the disease is most widespread among African Americans and indigenous Africans.

Disorders with similar symptoms

Experts name the following disorders, which in their symptoms may be close to galactosemia:

• galactokinase deficiency – the disease is associated with cataracts, increased levels of galactose in the blood and increased concentrations of galactitol in the urine. The latter accumulates in the lens of the eye, causing swelling of the latter, protein deposition and cataracts;
• deficiency of uridine diphosphate-galactose-4-epimerase - similar to the disease described above and manifests itself in the first months of life;
• Lactose intolerance is a metabolic disorder in which a person is unable to properly digest lactose;
• Neonatal hepatitis is a term used to describe liver dysfunction that occurs in the first months of life.

Diagnostics

Galactosemia can be diagnosed using a blood test. The first test is performed as part of standard screening immediately after the baby is born. The risk of a child developing the disease if both parents are carriers of the gene is 1 in 4.

Galactosemia can also be diagnosed in a patient using a urine test.

Treatment methods for galactosemia

The first and main method of treating the disease in question is a strict diet that completely excludes dairy products.

In especially severe cases, hormonal therapy is required. Specialists may also prescribe antibiotics.

Links[edit]

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Daily norm of galactose

The level of galactose in the blood should be kept at around 5 mg/dl of blood. The daily requirement of the substance can be easily reached if you consume enough dairy products and celery. Despite the fairly wide distribution of galactose, it is not found in food products in its pure form. Galactose in products must be determined by the presence of lactose in them.

A particularly strong need for galactose is experienced by:

• infants;
• women during breastfeeding;
• people actively involved in sports;
• people whose professional activities involve intense mental workload;
• people experiencing great stress;
• people who are often overtired.

The need for galactose may also be reduced in the following cases:

• in old age;
• if you are allergic to galactose or lactose;
• for diseases of the gastrointestinal tract;
• in the presence of inflammatory diseases of the female reproductive system;
• when establishing heart failure;
• with galactosemia.

II. Reactions based on hydroxyl groups

Reactions at the hydroxyl groups of monosaccharides are carried out, as a rule, in hemiacetal (cyclic) form.

1. Alkylation (formation of ethers).

When methyl alcohol acts in the presence of hydrogen chloride gas, the hydrogen atom of the glycosidic hydroxyl is replaced by a methyl group.

When using stronger alkylating agents, such as methyl iodide or dimethyl sulfate, such a transformation affects all hydroxyl groups of the monosaccharide.

2. Acylation (formation of esters).

When acetic anhydride acts on glucose, an ester is formed - pentaacetylglucose.

3. Like all polyhydric alcohols, glucose with copper (II) hydroxide gives an intense blue color (qualitative reaction).

Sources of galactose

Features of the use of galactose

The substance is very popular in the following areas:

• in medicine;
• in microbiology;
• in the preparation of sports nutrition;
• in the creation of gum food additives.

From a chemical point of view, the substance in question belongs to the class of reducing carbohydrates, capable of donating electrons by breaking its own oxygen bond.

The substance is most widespread in the food industry - it is added to create gum. Galactose is also valued by athletes - they take products containing the substance in question during intense physical activity.

Galactose in powder form

In medicine, galactose is used as a contrast agent for ultrasound diagnostics. Microbiologists use galactose as a means to help determine the type of microorganisms.

I. Reactions on the carbonyl group

1. Oxidation.

a) As with all aldehydes, oxidation of monosaccharides leads to the corresponding acids. Thus, when glucose is oxidized with an ammonia solution of silver oxide hydrate, gluconic acid is formed (the “silver mirror” reaction).

b) The reaction of monosaccharides with copper hydroxide when heated also leads to aldonic acids.

c) Stronger oxidizing agents oxidize not only the aldehyde group, but also the primary alcohol group into the carboxyl group, leading to dibasic sugar (aldaric) acids. Typically, concentrated nitric acid is used for such oxidation.

2. Recovery.

Reduction of sugars leads to polyhydric alcohols. Hydrogen in the presence of nickel, lithium aluminum hydride, etc. are used as a reducing agent.

3. Despite the similarity of the chemical properties of monosaccharides with aldehydes, glucose does not react with sodium hydrosulfite (NaHSO3).

Interesting facts about galactose

Galactose, unlike other chemical compounds, is practically insoluble in ordinary water.

The monosaccharide in question is not suitable for cooking.

Brain cells have the greatest need for galactose. Other organs also require the presence of the substance in the body.

Galactose is present even in lactose-free milk.

A person needs galactose from the first days of life. The first and main source of the substance in infancy is mother's milk. With age, the need for galactose decreases.

Biochemical characteristics

The formula of galactose is C6H12O6. A monosaccharide contains 6 carbon, 12 hydrogen and 6 oxygen molecules.

Galactose is a white crystalline powder. It dissolves very poorly in ethanol, and in water only at a temperature of +25 °C. Melting begins at +165-170 °C.

1 gram of galactose contains only 4 kcal. The glycemic index of the monosaccharide is 23 units. Thanks to these indicators, galactose is often called “smart sugar”. This is due to the fact that even a small amount provides a person with huge reserves of energy. In the body of mammals, the substance is synthesized from lactose.