D-(+)-Glucose
known as grape sugar or starch sugar or dextrose;
it is an aldohexose;
CHO
H
OH
it is found in fruit, in honey, in ripe grape. It is found in blood and in
urine in case of diabetes;
HO
H
H
OH
H
OH
CH2OH
"monomer" of starch, cellulose and glycogen;
physical aspect: white crystals;
taste: sweet, but less than sucrose (1 : 1.5);
it gives mutarotation (it is fast when warming or adding alkali);
it is reducing;
soluble in water, little in alcohol, almost insoluble in ether;
fermentable.
D-(-)-Fructose
CH2OH
O
HO
H
or Laevulose;
it is a ketohexose (one of the few which are known);
it is found in sweet fruits, in the inversion liquid of sucrose;
"monomer" of inulin;
H
OH
H
OH
CH2OH
physical aspect: white crystals;
taste: sweet, more than glucose;
in nature the furanosic form is widespread, in solid state it is
found in pyranosic form;
in water it gives mutarotation;
it is reducing;
soluble in water and alcohol, almost insoluble in ether;
fermentable with more difficulty with respect to glucose.
D-(+)-Galactose
CHO
or milk sugar;
H
OH
it is an aldohexose;
HO
H
it is found in lactose together with glucose;
HO
H
it is found in galactans (supply material of seeds and constituents of
OH
many gums);
H
CH2OH
physical aspect: crystals;
taste: sweet;
HNO3
in nature it is found in furanosic form, in solid state it is found in
pyranosic form;
COOH
in water it gives mutarotation;
OH
it is reducing;
HO
H
soluble in water;
HO
H
its oxidation with HNO3, as all galactans, gives mucic acid, compound
OH
with low solubility, from the determination of which, galactose can be
H
H
COOH
Mucic acid
quantitated.
fermentable, but with difficulties.
D-(+)-Mannose
It is an aldohexose;
it is obtained by hydrolytic break of mannans or by moderate
CHO
oxidation of mannite (mannitol);
HO
H
HO
H
taste: sweet;
H
OH
in nature the furanosic form is spread, at solid state it is found in
H
OH
pyranosic form;
CH2OH
physical aspect: amorphous substance;
in water it gives mutarotation;
It is reducing;
It is highly soluble in water;
fermentable.
L-(-)-Sorbose
It is a ketohexose;
It is found in sorbs, in figs, in carob pods where it is obtained
from the oxidation of sorbite (sorbitol);
It is obtained in large amount by bacterial oxidation of sorbite.
PENTOSES and PENTOSANS
The oligo and polysaccharides are mainly found in bran, cereals flour,
leaves, wood, gums.
pentoses are not fermentable.
L-(+)-Arabinose
• It is obtained by hydrolysis
contained in gums and mucilage.
D-(+)-Xylose
• “Wood sugar”;
of
hemicellulose
• it is very sweet;
• it is obtained by bran, by wood, leaves and gums.
D-(-)-Ribose
• It is found in animal and vegetable cells as
component of nucleoprotids.
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Disaccharids
They contain a glycosidic bond α or β between the hemiacetalic hydroxyl of a monose
and the alcoholic or hemiacetalic (diglycosidic bond) hydroxyl of another monose; in this
last case, the resulting disaccharide is no more reducing, while in the first case it is still
reducing since it has a free hemiacetal (or hemiketal) moiety (lactol);
CH2 OH
Maltose
(α-D-glucopyranosyl1,4-D-glucopyranose)
O
OH
OH
O
OH
OH
O
OH
Threalose (α-Dglucopyranosyl-1,1-α-Dglucopyranosyde)
CH2 OH
OH
nomenclature: the first monose (having the hemiacetalic function engaged in the
bond) has ending «-yl», the second monose has ending «-yde» if it is bonded to the first
one engaging its hemiacetalic function, otherwise its ending will be «-ose» (if it is bound
through one of its alcoholic hydroxyls);
they can be released by hydrolysis (acidic or enzymatic).
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SACCHAROSE (or SUCROSE)
HO
H
H
O
α
HO
HO
H
OH
O
H
H
CH2OH
H
O
β
H
OH
CH2OH
HO
H
(+)-α
α-D-glucopyranosyl-1,2-β
β-Dfructofuranosyde
-D-Gluco, D-fructo indicate D-glucose, D-fructose;
-α
α, β indicate the configuration of the two anomeric carbons;
-syl, -syde indicate that hemiacetalic and the hemiketalic OH is engaged
in the glycosydic bond;
-Pyrano-, -furano- indicate the pyranosic or furanosic form of the monose.
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sugar cane (or beet), it is the common “sugar” («table sugar»);
it is found in high amount in photosynthetic plants (as an energy
supply);
it is extracted from beet in Europe and from sugar cane in tropical
countries;
it is constituted by a molecule of glucose and one of fructose by a
diglycosydic bond;
it is not reducing;
it doesn’t give mutarotation;
it is dextrorotatory [α]D=+66.5°;
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it melts at 160°C;
at temperatures higher than 200°C it becomes caramel, used as colorant
in liquor, alcoholic and analcoholic beverages, etc.
with bases it forms saccharates, salts with low solubility.
QUANTITATIVE DETERMINATION
Measure of the rotatory angle;
measure of the density (saccharometer);
with Fehling, after its hydrolysis.
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INDUSTRIAL PREPARATION
Beets (usually containing about 15-20% of sucrose) are washed and cut, then put
in a series of diffusers at different temperatures where pure water passes.
H2O
35°C
50°C
50°C
70°C
75°C
Filtration
Extracted beets
Fresh beets
Brown juices are filtered and treated with milk of lime (suspension of CaOH) for
stopping fermentation processes and precipitating albuminoid and pectic
substances.
CaOH in excess is precipitated with CO2 (carbonatation).
The filtrate is concentrated at reduced pressure and saccharose precipitates. A syrup
remains (molasse) containing still 70-80 % of sugar. By evaporation of molasse and
subsequent centrifugation sugar is still obtained while the remaining liquid is used to
produce ethyl alcohol.
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LACTOSE (OR LACTOBIOSE)
OH OH
H OH
H
O
H
H
HO
H
H
OH
β
O
β
O
HO
H
H
H
OH
OH
H
(+)-β
β-D-galactopyranosyl-1,4-β
β-D-glucopyranose
“Milk sugar” (found in milk, it is the only disaccharide with animal
origin);
by hydrolysis it gives galactose and glucose;
lactobacillus
fermentable: lactic ferm. ⇒ Lactic acid (Yogurt, cheese)
alcoholic ferm. ⇒
ethyl alcohol
butyric ferm. ⇒ butyric acid
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It is obtained by milk whey: albumine is separated by boiling and
filtration; the filtered liquid is concentrated obtaining a syrup (5%
lactose), from which the sugar crystallizes.
it is dextrorotatory;
it is hydrolized by lactasis, enzyme which is often lacking in adults (⇒
intollerance);
It gives mutarotation;
it is used in pharmacy as laxative, as eccipient in tootpaste.
QUANTITATIVE DETERMINATION
oxidation to mucic acid from galactose;
with Fehling reactive (it has an hemiacetalic bond).
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MALTOSE
H
OH
H
O
α
HO
HO
H
H
H OH
H
OH
H
O
O
β
HO
H
H
OH
OH
H
α-D-(+)-glucopyranosyl-1,4-β
β-D-glucopyranose
“Malt sugar” (found in malt or in barley after hydrolysis of starch due
to amylase);
its hydrolysis (maltase enzyme) gives glucose;
it is reducing;
the anomeric C which is not engaged in the glycosidic bond can be
present in both the configurations (α or β).
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