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CARBOHYDRATES
KRAUSE'S FOOD & THE NUTRITION
CARE PROCESS(THIRTEENTH EDITION,
2012,chapter3)
Presentation by:
Dr. M. Ekramzadeh
PhD in Nutrition Science
Department of Nutrition
Shiraz University of Medical Sciences
‫‪‬‬
‫‪‬‬
‫گیاهان با اضافه کردن هیدروژن به‬
‫مولکول دی اکسیدکربن کم انرژی ‪،‬‬
‫انرژی را درمیان پیوند های کربنی‬
‫ذخیره میکند‪.‬‬
‫درخالل این فرآیند گیاه اولین‬
‫کربوهیدرات پایداررا که سه کربنی‬
‫است می سازد‬
‫کربوهیدرات های ‪ ،‬درشت مغذی های هستند که ازاتم های اکسیژن ‪،‬‬
‫هیدروژن و کربن تشکیل شده اند‪.‬‬
‫کربو هیدارت ها با واحد گرم اندازه گیری می شوند و هرگرم آنها ‪ 4 ،‬کیلو‬
‫کالری انرژی تولید می کنند‪.‬‬
Carbohydrates, including sugar and starch, are
widely distributed in plants and animals.
They perform multiple functions, ranging from being
structural components of deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA) (ribose and deoxyribose sugars) to
serving as sources of energy (glucose)
Glucose is derived from the breakdown of carbohydrates in
the diet (grains, starchy vegetables, and legumes) and in body
stores (glycogen), and by endogenous synthesis from protein
or the glycerol moiety of triglycerides
When energy intake exceeds expenditure, the excess
is converted to fat and glycogen for storage in adipose
tissue and liver or muscle, respectively
When energy expenditure exceeds calorie intake,
endogenous glucose formation occurs from the
breakdown of carbohydrate stores and from
noncarbohydrate sources (e.g., amino acids, lactate, and
glycerol)
CHEMISTRY OF CARBOHYDRATES
Carbohydrates are aldehyde or ketone derivatives of
polyhydroxy (more than one -OH group) alcohols, or
compounds
The term carbohydrate refers to hydrates of carbon and is
derived from the observation that the empirical formulas
for these compounds contain approximately one
molecule of water per carbon atom
glucose, C6H1206 : C6(H20)6
 lactose, C12H22011: C12(H20)11

 Major
source of energy
 Half the total calories in the diet
 composed of carbon, hydrogen, and oxygen in a ratio
of C: 0: H2
 Important dietary carbohydrates:
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
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monosaccharides
disaccharides and oligosaccharides
polysaccharides
MONOSACCHARIDES

Monosaccharides, or simple sugars, consist of a single
polyhydroxy aldehyde or ketone unit and cannot be
hydrolyzed to a simpler form

The backbone is made up of a number of carbon atoms

Sugars containing three, four, five, six, and seven
carbon atoms are known as trioses, tetroses, pentoses,
hexoses, and heptoses
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Monosaccharidesare termed aldose or ketose, according
to the position of the carbonyl group
Compounds that are identical in composition and differ
only in spatial configuration are called stereoisomers
The designation D or L refers to the position of the
hydroxyl group on the carbon atom adjacent to the last
(bottom) CH20H group
The D-sugars are written with the hydroxyl group on
the right and the L-sugars are written with the hydroxyl
group on the left
Most sugars in the human body are of the D-configuration
Hydroxyl groups inposition1 are then below the plane (α configuration) or above the plane (β-configuration)
Monosaccharides
 Do not normally occur as free molecules in nature but
as basic components of disaccharides and
polysaccharides
 Only a small number of the many monosaccharides
found in nature can be absorbed and used by humans
 Three to seven carbons
The most important are the six-carbon
hexoses: glucose, galactose, and fructose
These differences result from small but
significant differences in their chemical
structure, some resulting from the presence of
chiral carbons with four different atoms or
groups attached. These groups can occur in
different positions (isomers): glucose and
galactose (Figure 3-1)
The most important monosaccharide is
D . glucose = Blood sugar
The brain depends on a regular, predictable
supply, the body has highly adapted
physiologic mechanisms to maintain adequate
blood glucose levels
Fructose is the sweetest of all monosaccharides
Epidemiologic evidence suggests that high-fructose
diets (including intake from sweetened beverages)
may contribute to obesity and other health conditions,
such as the metabolic syndrome
Both galactose and fructose are metabolized in the
liver by incorporation into metabolic pathways for
glucose, but fructose bypasses a major control
enzyme in the glycolytic pathway
Galactose is produced from lactose by
hydrolysis during the digestive process
Infants born with an inability to metabolize
galactose have galactosemia
Disaccharides
Three most important disaccharides in
human nutrition are:
sucrose, lactose, and maltose
These sugars are formed from
monosaccharides joined by a glycosidic
linkage between the active aldehyde or ketone
carbon and a specific hydroxyl on another
sugar
FIGURE 3-3 Disaccharides of importance in humans: sucrose (glucose
and fructose) and lactose (glucose and galactose)
Sucrose occurs naturally in many foods and is also
an additive in commercially processed items
Invert sugar is also a natural form of sugar (unlinked
glucose and fructose in a 1: 1 ratio) that is used
commercially because it is sweeter than equal
concentrations of sucrose
Invert sugar forms smaller crystals than sucrose and
is preferred in the preparation of candies and icings
Honey is an invert sugar.
Invert Sugar
Inverted or invert sugar syrup is a mixture of glucose and
fructose; it is obtained by splitting sucrose into these two
components. Compared with its precursor, sucrose, inverted
sugar is sweeter and its products tend to retain moisture and
are less prone to crystallization. Inverted sugar is therefore
valued by bakers, who refer to the syrup as invert syrup.
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Notable uses
Honey is a mixture (principally) of glucose and
fructose, giving it similar properties to invert syrup.
This gives it the ability to remain liquid for long
periods of time.
Jam, when made, produces invert sugar during
extensive heating under the action of the acid in the
fruit.
Cigarettes use inverted sugar as a casing to add
flavour
Lactose is made almost exclusively in the
mammary glands of lactating animals.
Maltose is seldom found naturally in the food
supply but is formed by hydrolysis of starch
polymers during digestion and is also
consumed as an additive in numerous food
products.
Oligosaccharides are small (3-10 monosaccharide
units), readily water soluble, and often sweet
Enzymes found in the brush border of the intestine
break bonds between molecules in disaccharides and
are specific to the particular bond
Larger molecules with linkages that are different are
not digestible and are classified as dietary fiber
‫اولیگوساکاریدها ‪:‬‬
‫‪‬ترکیباتی هستند که دارای ‪ 20-3‬مولکول مونوساکارید می باشند‪ .‬برای مثال ‪:‬‬
‫‪‬تری ساکارید موجود درچغندر ‪ ،‬رافینوز (گاالکتوز‪+‬گلوکز‪+‬فروکتوز) می باشد‪.‬‬
‫‪‬تترا ساکارید موجود درحبوبات و کدو ‪ ،‬استاکیوز (گاالکتوز‪+‬گاالکتوز‪+‬گلوکز ‪+‬‬
‫فروکتوز) می باشد‪.‬‬
Thanks