Classification of carbohydrates.ppt

Carbohydrates are generally classified into monosaccharides (simple sugars), oligosaccharides (containing few sugar units) and polysaccharides (containing many sugar units).
Monosaccharides are sugar molecules containing short chain of carbon atoms, one aldehydic or ketonic group and hydroxyl groups attached to remaining Carbon atoms.
Oligosaccharides are formed by polymerisation of monosaccharide molecules by elimination of water molecules.
Polysaccharides are high molecular weight substances composed of large number of moosaccharide units combined to form one large polymer molecule. They may be straight chain or branched chain polymers.

1. CLASSIFICATIONOFCARBOHYDRATES
Mrs. R.Subha, M.Sc., M.Phil., D.C.T.,
Assistant Professor of Home Science

2. INTRODUCTION
Carbohydratesaregenerallyclassifiedinto
monosaccharides(simplesugars),oligosaccharides
(containingfewsugarunits)andpolysaccharides
(containingmanysugarunits).

3. MONOSACCHARIDES
Monosaccharides are sugar molecules containing short
chain of carbon atoms, one aldehydic or ketonic group
and hydroxyl groups attached to remaining Carbon
atoms.
If they contain aldehyde group, they are named as
aldoses and if they contain ketone group they are
named as ketoses.
Depending on number of Carbon atoms,
monosaccharides are named astrioses (3 C atoms),
tetroses (4 C atoms), pentoses (5 C atoms), Hexoses (6
C atoms) and so on.

4. MONOSACCHARIDES -EXAMPLES
1. Trioses, C
3H
6O
3, e.g. glyceraldehydes and dihydroxy
acetone
2. Tetroses, C
4H
8O
4, e.g. erythrose, threose
3. Pentoses, C
5H
10O
5, e.g. arabinose, xylose, ribose,
deoxyribose
4. Hexoses, C
6H
12O
6, e.g. glucose, galactose, fructose,
mannose

5. IMPORTANTMONOSACCHARIDES
1. D-glucose or Dextose: It is the building block of
starch and cellulose, source of energy for the
animals.
2. Fructose: It is found in fruits and honey.
Alongwith glucose, it is present in cane sugar
(sucrose).
3. Galactose: It is not found in free state in foods
but it is component of milk sugar (lactose) and
agar-agar.
4. Arabinose and xylose : They are pentoses and
found in plant gums.

6. PROPERTIESOFMONOSACCHARIDES
1. They are called as reducing sugars because they
reduce Cu
2+
and Fe(CN)
6
3+
ions.
2. The reducing sugars are oxidized to sugar acids. E.g.,
Glucose is oxidized to gluconic acid (monocarboxylic
acid) and glucaric acid (dicarboxylic acid).
3. Reduction of monosaccharides yield sugar alcohols.

7. OLIGOSACCHARIDES
Oligosaccharidesareformedbypolymerisationof
monosaccharidemoleculesbyeliminationofwater
molecules.
Dependingonnumberofmonosaccharideunits,
oligosaccharidesareclassifiedasdi-,tri-tetra-
saccharidesetc.
Thelinkagebetweenmonosaccharideunitsin
oligosaccharideunitsisglycosidiclinkage.

8. IMPORTANTOLIGOSACCHARIDES
Sucrose:Itismostabundantinsugarcaneand
sugarbeet.Itconsistsofonemoleculeofglucoseand
onemoleculeoffructose,joinedtogetherbyglycosidic
linkagebetweentheiranomeric–OHgroups.Sucrose
isthusnon-reducingsugar.
Maltose:Itistheintermediateproductofstarch
hydrolysis.Itconsistsoftwomoleculesofglucoseunits
withglycosidiclinkagebetweenanomericCofone
moleculeand–OHmoleculeonC-4oftheother.
Maltoseisreducingsugar.
Lactose:Itisfoundonlyinmammalianmilk.Itconsists
ofonemoleculeofglucoseandonemoleculeof
galactose.

9. POLYSACCHARIDES
They are high molecular weight substances composed
of large number of monosaccharide units combined to
form one large polymer molecule.
They may be straight chain or branched chain
polymers.

10. IMPORTANTPOLYSACCHARIDES
Starch:Itoccursincerealgrains,pulses,tubers,fruitsetc.It
isthemajorsourceofenergyindietofman.Starchisa
polymerofglucose.Starchisamixtureoftwosubstances,
about25%amylose(straight-chainpolymer)and75%
amylopectin(branchedchainpolymer).Becauseofthe
structuraldifferencesbetweenamyloseandamylopectin,
theyexhibitdifferentproperties.Amylosecontributestogel-
formationwhileamylopectinisresponsibleforthickness
propertiesoffoodscontainingstarch.
Dextrin:Itistheproductofpartialhydrolysisofstarch.Their
propertiesareintermediatebetweenthoseofsugarsand
starch.Theyareproducedwhenstarchissubjectedtodry
heat.E.g.duringtoastingofbread.
Glycogen:Glucoseisstoredintheformofglycogenin
animaltissues.Itismainlyfoundinliverandmuscles.Itis
similarinstructuretoamylopectinbutismorebranchedthan
amylopectin.

11. IMPORTANTPOLYSACCHARIDES
Cellulose:Itisastraightchainpolymerofglucose
molecules.Theglycosidiclinkagesaredifferentincellulose
andamylose.Celluloseisinsolubleinwater.Itisnot
digestedinhumantract.Modifiedcelluloseisusedinfood
industries.Carboxymethylcelluloseisusedinicecream.
Pecticsubstances:Theyareconstituentsofplantcell
wall.Theyaremixturesofpolysaccharidesformedfrom
galactose,arabinoseandgalacturonicacid.Pectin,awater
solublecomponentispresentinfruitsandformsgelwith
sugarandacid.
Gums:Theyarehydrophilicsubstancesthatgiveaviscous
solutionordispersionwhentreatedwithhotorcoldwater.
Starches,pectcicsubstancesandderivativesofstarchand
celluloseareincludedinthiscategory.Theyactas
thickeners,moistureretainers,emulsionstabilizers,foam
stabilizers,clarifyingagents,etc.Importantgumsinclude
Gumarabic(obtainedfromAcaciaplant),Agar(obtained
fromred-brownalgae)andalgin(obtainedfrombrown
algae).

12. REFERENCES
Satyanarayana U. & Chakrapani U. (2011),
“Biochemistry”. Books and Allied (P) Ltd.
N. Shakuntala Manay & M. Shadaksharaswamy (2001),
“Foods: Facts and Principles”. New Age International
Publishers.