3. DISACCHARIDES
• When two monosaccharides units joined covalently by O- glycosidic
linkage, a disaccharide is formed.
• The important disaccharides are:
• 1. Sucrose
• 2. Maltose and isomaltose
• 3. Lactose
4. Sucrose
• It is the sweetening agent known as cane sugar/table sugar. It is
present in sugarcane and various fruits.On hydrolysis,it yields 1 mol of
D-glucose and 1 mol of D-fructose.
5. Sucrose
• Sucrose is non- reducing sugar; so it gives negative benedicts test,no
mutarotation and will not form osazone. This is because the linkage
involves first carbon of glucose and second carbon of fructose, and
free reducing groups (anomeric C) are not available.
Structure of sucrose (1–2 linkage)
6. Sucrose
• When sucrose is hydrolyzed, the products have reducing action.
• A sugar solution which is originally non-reducing, but becomes
reducing after hydrolysis, is inferred as sucrose.
Benedict's test is positive for glucose.
Test is negative for sucrose; but when
sucrose is hydrolyzed, the test becomes
positive.
7. Sucrose
• Sucrose is dexorotatory ,+66.5 (because glucose is dextrorotatory (52.5) and fructose in
furanose form is also dextrorotatory).
• On Hydrolysis of sucrose ,its fructose released in furanose form is unstable,immediately
changes to pyranose form,which is levorotatory(-92),levorotatory activity of fructose is
more than dextrorotatory activity of glucose. Therefore, the products will change the
dextrorotation to levorotation, or the plane of rotation is inverted.
• Equimolecular mixture of glucose and fructose thus formed is called invert sugar. The
enzyme producing hydrolysis of sucrose is called sucrase pesent in intestine.
• Honey contains enzyme invertase which convert sucrose to invert sugar.
• Invert sugar is sweeter than sucrose.
8. SUCROSE
• Sucrose like other disacharides ,can be utilized in body if taken by
mouth because specific enzyme,sucrase ,present only in intestine
which hydrolyses it to glucose & fructose,which are absorbed,
• If given by i/v inj……….?
• Excreted as such in urine
9. Lactose
• It is the sugar present in milk.
• It is a reducing disaccharide.
• On hydrolysis lactose yields glucose and galactose.
• Beta glycosidic linkage is present in lactose.
Lactose
10. Lactose
• The structure is given in Figure. The anomeric carbon atom of beta-
galactose is attached to the 4th hydroxyl group of glucose through
beta-1,4 glycosidic linkage.
• The lactose may be alpha or beta variety, depending on the
configuration of 1st carbon of glucose moiety.
Lactose
11. Lactose
• Lactose forms osazone which resembles "pincushion with pins" or
"hedgehog" or flower of "touch-me-not“ plant.
13. LACTULOSE
• It is synthatic disacharide made up of Galactose &Fructose.It is not
digested in GIT but act as osmolar laxative used to treat constipation.
15. Lactose
• Lactose is a disaccharide of β-D-galactose and β-D-glucose in β(1,4)
linkage.
• Human milk contains 200mmol/lit of lactose.
• It is digested by enzyme lactase to form glucose and galactose in the
brush border of the intestine.
16. Lactose containing food stuffs
• Fresh, skimmed , non fat and condensed milk.
• Cream
• Cheese
• Processed foods
• Stuffings
• Salad dressings etc.
17. Lactose intolerance
• Lactose intolerance, also called lactase deficiency or hypolactasia, is
the inability to digest and metabolize lactose, a sugar found in milk.
• Lactose intolerance is not an allergy because it is not an immune
response but caused by lactase deficiency.
18. Lactose intolerance
• Lactose intolerance can occur in any age group or population.
• However, people of African, Jewish, Hispanic, Asian, Middle Eastern
and Native American descent, Caucasians are at risk for developing
lactose intolerance.
19.
20. Symptoms
• Abdominal bloating and cramps
• Flatulence
• Diarrhoea
• Nausea
• Borborygmi (audible sounds by intestinal movements-gurr-gurr)
• Vomiting (particularly in adolescents).
21. Types of lactase deficiency
• Primary lactase deficiency is a genetically determined absence or
decrease in the enzyme is noted.
• Jejunal morphology is normal.
22. Secondary lactase deficiency
• Secondary, acquired, or transient lactase deficiency is due to the
small intestinal mucosal disease, abnormalities of brush border cells
and transport processes.
• It is often associated with celiac sprue(gluten allergy).
23. Diagnosis
• Dietary history of the patient who are complaining flatulance ,
abdominal pain , diarrhoea.
• Familial history of the patient.
• Check whether the patient has underwent partial gastrectomy and
other related procedures.
• Tests – stool acidity test, hydrogen breath tests (equipment -not in
pak).
24. Management
• Avoiding lactose-containing products
• Alternative products such as Plant-based milks and derivatives are
inherently lactose free: soy milk, rice milk, almond milk, hazelnut
milk, oat milk, peanut milk-not available in pak-costly
• Tab Lactase-not in pak
Lactose free formula milk now available-NL-33,AL 110,etc.
25. Maltose
• Maltose contains two glucose residues.
• There is alpha-1,4 linkage, i.e. the anomeric 1st carbon atom of one
glucose is combined with 4th hydroxyl group of another glucose
through alpha-glycosidic linkage. Structure is shown in Figure.
Maltose
26. Maltose
• Maltose may be alpha or beta depending on the configuration at the
free anomeric carbon atom.
• It is a reducing disaccharide. It forms petal-shaped crystals of
maltose-osazone.
27. Isomaltose
• It is also a reducing sugar. It contains 2 glucose units combined in
alpha-1, 6 linkage. Thus first carbon of one glucose residue is attached
to the sixth carbon of another glucose through a glycosidic linkage.
Isomaltose
28. Isomaltose
• Partial hydrolysis of glycogen and starch produces isomaltose.
• The enzyme oligo-1,6-glucosidase present in intestinal juice can
hydrolyze isomaltose into glucose units.
