Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen that serve as an important energy source. They include sugars (monosaccharides and disaccharides) and starches/fibers (polysaccharides). Monosaccharides like glucose cannot be broken down further, while disaccharides like sucrose break down into two monosaccharides. Polysaccharides provide structure or store energy and break down into many monosaccharides. Carbohydrates are found widely in plants and are produced through photosynthesis. They are classified based on their structure and whether they are digestible or provide structure. Identification tests can determine the type of unknown carbohydrate sample.

1. Carbohydrates
Carbohydrates are broadly defined as polyhydroxy aldehydes or ketones and their
derivatives or as a substances that yields one of these compounds.
 Composed of carbon, hydrogen, and oxygen
 Functional groups present include hydroxyl groups
 -ose indicates sugar
 Formula for carbon hydrates is Cn (H2O)n
Fig#01 depicts the carbohydrates contained in food eating items
Occurrence ofcarbohydrates
• Carbohydrates are widely distributed in plants and animals and also found in green
plants by the process of Photosynthesis.
• This process occurs with the presence of Chlorophyll Pigment.
• These carbohydrates utilized by the animals in the form of food.
• Well known carbohydrates are Glucose (C₆ H₁ ₂ O₆ ) , Sugar (C ₁ ₂
H₂ ₂ O₁ ₁ ),Starch (C ₆ H₁ ₀ O ₅ )
&Cellulose (C ₆ H₁ ₀ O ₅ )n used by human beings & animals.
• Animals can synthesize Carbohydrates from Fat& protein.
Carbohydrates are the most abundant ofall the organic compounds in
nature.
In plants, energy from the Sun is used to convert carbon dioxide and water into the
carbohydrate glucose.
 Many of the glucose molecules are made into long-chain polymers of starch that
store energy.
 About 65% of the foods in our diet consist of carbohydrates.
 Each day we utilize carbohydrates in foods such as bread, pasta, potatoes, and rice.
6CO₂ +6H₂O C₆ H ₁₂ O₆ + 6O₂
chlorophyll
sunlight

2.  Other carbohydrates called disaccharides include sucrose (table sugar) and
lactose in milk.
 During digestion and cellular metabolism, carbohydrates are converted into
glucose, which is oxidized further in our cells to provide our bodies with energy
and to provide the cells with carbon atoms for building molecules of protein, lipids,
and nucleic acids.
 In plants, a polymer of glucose called cellulose builds the structural framework.
Cellulose has other important uses, too.
 The wood in our furniture, the pages in your notebook, and the cotton in our
clothing are made of cellulose.
Classification of Carbohydrates
• Carbohydrates are classified according to the number of subunits that make them up
3 Types of Carbohydrates
 Monosaccharides
 Oligosaccharides
Disaccharides
Trisaccharides
Tetrasaccharides
 Polysaccharides
Monosaccharides are simple sugars, or the compounds which possess a free aldehyde
(CHO) or ketone (C=O) group and two or more hydroxyl (OH) groups. They are the
simplest sugars and cannot be hydrolyzed further into smaller units
Table#01 showsName ofsugar, structural formula and examples of
Aldoses and ketoses
Sugar Structural
formula
Aldose Ketose
trioses C3 Glyceraldehyde Dihydroxyacetone
tetroses C4 Erythrose,
Threose
Erythrulose
pentoses C5 Xylose, Ribose,
Arabinose
Ribulose
hexsoses C6 Glucose,
galactose,
mannose
fructose

3. Table#02 shows structure of different
carbohdrates
Steriochemistry
Optical isomers (= enantiomers) differ from each other in the disposition of the various
atoms or groups of atoms in space around the asymmetric carbon atom. These are, in fact,
the mirror image of each other. These may also be likened to left- and right-handed gloves.
One form in which H atom at carbon 2 is projected to the left side and OH group to the right
is designated as D-form and the other form where H atom is projected to the right side and
OH group to the left is called as L-form (note the use of small capital letters D and L)
For example, the glyceraldehyde has only one asymmetric carbon atom (numbered as 2) and
it can, therefore, exist in 2 isomeric forms :
Fig#02
depicts the
structure of D-
glyceraldehyde
and L-
glyceraldehyde
D-glucose
“dextrose”
Blood sugar
D-galactose D-fructose
“Levulose”
Fruit sugar

4. Carbohydrates with free carbonyl groups or in hemiacetal form give positive tests to Benedict’s
and Fehling’s reagents. Without having been hydrolyzed are referred as ‘reducing’ sugars
others (i.e., the acetal types) are then ‘non-reducing’ sugars
Table#03 shows
the properties of
reducing and
non-reducing
sugar
Oligosaccharides
These are compound sugars that yield 2 to 10 molecules of the same or different
monosaccharides on hydrolysis.
Accordingly, an oligosaccharide yielding 2 molecules of monosaccharide on hydrolysis is
designated as a disaccharide.
Disaccharides(C₁₂H₂₂O1₁):
 On hydrolysis yields 2 molecules of Monosaccharide's. – e.g.
Sucrose, Lactose, Maltose, Cellobiose, Trehalose, Gentiobiose,
Melibiose
E.g.: Sucrose Glucose + Fructose.
Maltose Glucose + Glucose.
–cells can make disaccharides by joining two monosaccharides by biosynthesis.
Glucose + fructose = sucrose
 Table sugar
 Found naturally in plants: sugar cane, sugar beets, honey, maple syrup
 Sucrose may be purified from plant sources into Brown, White and Powdered Sugars.
Glucose + galactose = lactose
 The primary sugar in milk and milk products.
 Many people have
problems digesting large
amounts of lactose
(lactose intolerance)
Glucose + glucose = Maltose
 Produced when starch breaks down.
Used naturally in fermentation reactions of alcohol and been manufacturing.

5. FIG#03 Depicts the structure of sucrose,
lactose and maltose
Trisaccharides (C₁₈H₃₂O₁₆):
 On hydrolysis yields 3 molecules of Monosaccharide's. e.g.: Raffinose (Formed
by one mole of each i.e. glu, fruc, galac)
Eg: Raffinose Glucose + Fructose + Galactose.
Rhaminose Rham + Rhamnose + Gelactose.
Tetrasaccharides ( C₂₄H₄₂O₂₁):
 On hydrolysis yields 4 molecules of Monosaccharide's.
Eg: Stachyose Glucose + Fructose + Galactose + Galactose.
Fig#04 depicts the artificial sweetner

6. Table#04 relative sweetnessofsugars and artificial sweetners
POLYSACCHARIDES (C6H10O5)n:
Containing 10 or more monosaccharide units attached together
 On hydrolysis it produce Indefinite no. of Monosaccharide's molecules called as
Glycans.
 Common Polysaccharides of biological significance are Starch , Glycogen(Animal
starch),Cellulose , Inulin.
 Starch-Glucose units joined by α-1,4& α-1,6 linkages.
 Cellulose-Glucose units joined by β -1,4 linkages.
 Important derivatives-Gums & Mucilage's
 Gums- consists of Ca , K & Mg salts of complex substances called Polyuronides. on
prolonged boiling with dilute acids they yields sugar and uronic acids. Mucilage's –
Sulphuric acid esters.

7. • Examples
1. Starch- digestible
2. Glycogen- digestible
. Fiber- indigestible
Long chains of glucose units form these polysaccharides
• Cellulose gives structure to plants, fiber to our diet
• Glycogen is an energy storage sugar produced by animals
• Liver cells synthesize glycogen after a meal to maintain blood glucose levels
A great majority of carbohydrates of nature occur as polysaccharides
Chemically, the polysaccharides may be distinguished into
Homopolysaccharides,
 which yield, on hydrolysis, a single monosaccharide.
Heteropolysaccharides,
 which produce a mixture of monosaccharides on hydrolysis. Based on their
functional aspect, the polysaccharides may be grouped under two heads :
(a)Nutrient (or digestible) polysaccharides.
 These act as metabolic reserve of monosaccharides in plants and animals, e.g.,
starch, glycogen and inulin.
(b)Structural (or indigestible) polysaccharides.
 These serve as rigid mechanical structures in plants and animals, e.g., cellulose,
pectin and chitin and also hyaluronic acid and chondroitin.
Fig#05 flowsheetof carbohydrates
Types of Polysaccharides
1. Starch
o The major digestible polysaccharide in our diet.
o The storage form of carbohydrate in plants.

8. o Sources: Wheat, rice, corn, rye, barley, potatoes, tubers, yams, etc.
 – Two types of plant starch: 1. Amylose 2. Amylopectin
Fig#06 Structure of starch
Amylose:
It is in the form of straight chain linked together with α- 1-4, linkages indicating
300 – 5,500 glucose units per molecules, molecular wt range from 105 to 106.
Generally it is water soluble and gives blue colour with iodine.
Amylopectins:
It contain beside straight chain several branched chains, which are arranged in α—1-
4 and β-1-6 linkage units, one molecule of amylopectin contains 50,000 to 5,00,000
glucose molecules, molecular wt. range from 107 to 108, it is insoluble in water and
gives purple colour with iodine .
FIG#07 STRUCTUREOF AMYLOSE AND AMYLOPECTIN

9. Types of Polysaccharides
2. Cellulose
• form cell walls in plant cells
• also called fiber or ruffage
• indigestible by humans.
FIG#08 STRUCTURE OF CELLULOSE
Fig#09 the polysaccharide cellulose is composedofglucose units
connectedby B-1,4-glycosidic linkage
Types of Polysaccharides
3. Glycogen
• The storage form of glucose in the body.
• Stored in the liver and muscles.

10. • Found in tiny amounts in meat
sources. Not found in plants.
• Not a significant food source of
carbohydrate.
fig#10 structure of glycogen
Physical and chemical properties of
carbohydrates
 Monosaccharides:
• Crystalline compounds.
• Soluble in water.
• Sweet to taste .
• Needs digestion in-order to be absorbed in blood
stream.
 Disaccharides:
• Crystalline compounds.
• Soluble in water
• Sweet to taste.
• Must be digested to monosaccharide's before
absorbed and used for energy.
• Polysaccharides:
• Amorphous compounds.
• Not Soluble in water.
• Not Sweet to taste.
• They form colloidal suspensions instead of
solution & must be digested before being
absorbed.

11. Table#05 Classificationof carbohydrates
Table#07 Carbohydrates and their food resources

12. IDENTIFICATION OF AN UNKNOWN CARBOHYDRATE
Step1- Perform Molischtest
Observation-Reddish violet ring at the junction of two liquids.
Inference- Carbohydrate is confirmed.
Step-2- Perform Iodine test
Observation- No change in color
Inference- Mono or disaccharide
Note- Blue, brown or red color is given by starch, glycogen and dextrins respectively
Step-3- Perform Benedict’s test
Observation Positive reaction (green, yellow, orange or red colored ppt)
Inference- The given carbohydrate is reducing in nature, it could be glucose,
fructose, galactose, maltose or lactose. Note- Sucrose gives a negative reaction with
Benedict's reagent.
Step-4- Perform Barfoed’s test
Observation- A scanty red ppt at the bottom of the test tube
Inference- A reducing mono saccharide is present, it may be glucose, fructose,
mannose or galactose
Note- The test is negative for disaccharides like, lactose, maltose and sucrose as
well.
Step-5- Perform Seliwanofftest
Observation- A cherry red color is observed
Inference- Fructose is confirmed.
Note- Glucose, galactose and mannose give a negative result with seliwanoff test.
Sucrose gives a positive reaction with seliwanoff test.
Step-6- Perform osazone test (If fructose is confirmed, osazone test
is not required)
Observations-
Needle shaped crystals- Glucose, fructose or mannose
Sun flower shaped crystals- Maltose is confirmed
Powder puff/ hedge hog crystals- Lactose is confirmed
Step-7- Perform hydrolysis test
If the Benedict’s, Barfoed’s tests are negative and seliwanoff test is positive, the
carbohydrate is essentially sucrose, for confirmation proceed with
inversion/hydrolysis test
Observation- Benedict’s and Barfoed’s test react positively with hydrolytic products.
Inference- Sucrose is confirmed

13. REFERENCES:
 JAIN, J.L. (2005) Fundamentals of Biochemistry, S. Chand & Company Ltd. Ram
nagar, New Delhi, India
 KAREN C. TIMBERLAKE (2012) Chemistry : An Introduction to General,
Organic, and Biological Chemistry -11th ed.Publishing as Prentice Hall in the
United States of America.
 SATYANARAYANA, U. (2007) Biochemistry , Books and Allied (P) Ltd,
Kolkata, I
 C.k.KOKATE , A.PUROHIT, S.B GOKHALE ,Biochemistry Pg.no:7.1-7.20.
 T.E WALLIS ,Text book of Pharmacognosy , Pg.no:62-89.
 VINOD.D. RANGARI,Pharmacognosy and phytochemistry part-2 , Pg.no:195-
211.
 BELITZ.H.D.GROSCH,WSCHIEBERLE.P (2009) “Food chemistry”4th ed.
Springer.
 Nelson DL,CoxMM(2005).Lehning’s Priciples of biochemisrty (4th ed).New
york, W.H Freeman and company.
 Lodish, Harvey; Berk, A., Amon, A., Bretscher, A., Kaiser, C., Kriefer, M.; et al.
(2013).Molecular cell biology (7th ed.). New York: W.H. Freeman and Co.
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