Phyto 1
Lecture 7
Carbohydrates Part
Lecture 7
Non-reducing disaccharides
Sucrose
Name
Structure
Methods of
Preparation
Trehalose
(Glc-1α-1α-Glc)
Two glucose attached together
(Saccharose, Table sugar, Cane Sugar,
Beet sugar)
- Anomeric Carbon-1 of glucose is linked to the anomeric carbon-2 of
fructose.
-Thus, BOTH anomeric carbons are involved in glycoside bonds.
-Therefore, sucrose is not a reducing sugar( not contain free hemiacetal gp both aldehydic gp and ketonic gp involved in linkage )
The linkage between the two anomeric carbons of the two
glucose units (C1- C1) therefore, none reducing (for same
reason of sucrose )
Preparation of Sucrose:
A) From sugar-cane (Saccharumofficinarum)
B) From sugar beet (Beta vulgaris)
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Uses
Chemical Test
A) Preparation from sugar-cane(Saccharumofficinarum):
● Alkalinize the juice of sugar cane with Ca(OH)2 (to neutralize the
plant acids & avoid hydrolysis)
● Heat to coagulate proteins, which are skimmed
● Filter & concentrate
● Leave to crystallize raw sugar. (repeat crystallization)
● The dark syrup left after second crystallization is called molasses OR
blackstrap after third crystallization
● The raw sugar is refined by decolorization with charcoal & is
recrystallized after concentration under vacuum.
■ Nutrients and demulcent
As sweetener and stabilizer in food industry.
■In the preparation of syrups and molasses (sweeting agent )
Stabilizing cell membranes and has a suppressive effect on
■ In moderate aqueoussolution, sucrose is bacteriostatic (stop growth
osteoporosis development
of bacteria) & used as preservative (66%w/v).
■It masks disagreeable taste in tablets & pills
■It retards oxidation in certain preparations.
■It is used as excipient for tablets
■In preparation of dextran (a polysaccharide used as plasma substitute)
by action of certain bacteria
1) Sucrose + heat
(200-2500C) amorphous brown substance as
caramel (used as flavouring and colouring matter).
2) Sucrose + cobalt nitrate + NaOH
violte color (special test of
sucrose)
3) Sucrose + HCl /resorcinol
Red Color (seliwanoof's test rapid
furfural{special test of fructose})
4) Sucrose + Fehling's solution
-ve (non-reducing)
5) Sucrose + osazone test
-ve (non-reducing)
6) Sucrose solution doesn't undergo mutarotation (aldehydic gp of c1 in
glucose attached to beta ketonic gp of fructose can’t mutarotate)
7) –ve with barfoed’s
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Others
Hydrolysis of sucrose
-The enzymatic (α-glucosidase&invertase) or dil acid hydrolysis of
sucrose is called “inversion” due to the fact that:
In mushrooms: contains up to 10-25 %.
The sign of rotation being changed from (+) in the original solution of
sucrose into (-) {sign of fructose }in the hydrolyzed solution, the process
is called inversion
Molasses:
Molasses is a thick, brown to deep black or dark brown, honey-like
substance made when cane or beet sugar is processed by boiling to
crystallize sucrose. It is used as a sweetener and food supplement in
many countries.
- Nutritional Profile
-Molasses (from second crystallization_ is an excellent source of
manganese, copper, iron, calcium, potassium and magnesium.
-blackstrap molasses (from third crystallization) is a good source of
vitamin B6 and selenium.
Nutrients in Blackstrap Molasses of 2 tsp (13.67 grams) Nutrient % Daily
Value
Mg 18%, Cu 14%, Fe 13.2%, Ca 11.7%, K 9.7%,Mn 7.3%,
vit B 65%, Se 3.4%, Calories (32) 1% ( ) االرقام مش حفظ
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Reducing disaccharides
The reducing properties of disaccharides are due to the presence of free hemi-acetal gp in their molecule
Reducing dihexoses are classified according to the site (position) of the linkage into
C1-C3 / C1-C4 / C1-C6 dihexoses
The most common are those of the C1-C4 gp e.g. maltose & lactose
Reducing C4 Dihexoses Reducing disaccharides
Name
Maltose
Lactose
malt sugar
Glc-α1-4-Glcmaltase 2 glucose
milk sugar , Gal-β1-4 Glc
Glcβ 1- 4Glc
It consists of two glucose units,
linked by β linkage
Structure
Source
Cellobiose
In malt and germinating cereals
Lactose is the principal sugar of mammalian
milk.
cellulose (cotton fibre or filter paper)
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Properties
and
Reactions
Methods of
Preparation
• Reduction: + ve Fehling’s soln and –ve Barfoed’s
soln.
• It forms osazone (rosettes of plates or broad
needles).
By partial acid hydrolysis of starch or dextrin or by
action of b-maltase enzyme.
Gal-β1-4 Glc + β- galactosidases
β-Galactose + α-Glucose
+ve Fehling’s but –ve Barfoed’s
solution.
Characteristic osazone (needles
aggregated in clusters or tufts).
Obtained from whey (a by-product of cheese
manufacture) after concentration, upon
which deposits of lactose crystallize out.
Glcβ 1- 4Glc + β -glucosidases (emulsin)
β-Glc + Glc
Obtained from cellulose (cotton fibre
or filter paper) by either careful acid
hydrolysis or by the action of cellulase
enzyme.
Nutrient in infant foods, since it is less
Sweet than sucrose and more easily
digested.
Inert diluent for other drugs.
Uses
Others
It exists in two anomeric forms α-maltose and βmaltose, which undergo mutarotation.
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Name
Structure
Source
Properties
Methods of
Preparation
Reducing C3 Dihexoses Reducing disaccharides
Reducing C5 Dihexoses Reducing disaccharides
Turanose
Gentiobiose
(Glc-α1-3β-Frc)
(Glc- β1-6-Glu)
tri saccharide melezitose
Glcα-1- 3 β-Frc + β–glucosidases(emulsin)
α-Glc + β-Frc
It is obtained from the tri saccharide melezitose by careful acid
hydrolysis
trisaccharidegentianose
Glcα-1- 6 βGlc+ β–glucosidases(emulsin)
β-Glc + Glc
It is obtained from the trisaccharidegentianose, but also occurs in
someglycosides, e.g. amygdalin.
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Trisaccharides & Tetrasaccharides
Trisaccharides) Gentianose – Raffinose)
Tetrasaccharides
Raffinose
Stachyose
Names
Structure
melitriose or gossypose
Source
Properties
Found in beet, cottonseed & soybean
Raffinose is a non-reducing trisaccharide
In the tubers of Stachystuberifera (Japanese artichoke) and soybean
On complete acid hydrolysis it yields D-fructose, D-glucose and two
molecules of D-galactose.
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