Post on 31-Dec-2015
CARBOHYDRATES
KRAUSE'S FOOD & THE NUTRITIONCARE PROCESS(THIRTEENTH EDITION,
2012,chapter3)
Presentation by:Dr. M. EkramzadehPhD in Nutrition ScienceDepartment of NutritionShiraz University of Medical
Sciences
گیاهان با اضافه کردنهیدروژن به مولکول
دی اکسیدکربن کم انرژی ، انرژی را در
میان پیوند های کربنی ذخیره میکند.
در خالل این فرآیندگیاه اولین
کربوهیدرات پایدار را که سه کربنی است
می سازد
کربوهیدرات های ، درشت مغذی های هستند که از اتم های اکسیژن ، هیدروژن و
.کربن تشکیل شده اند
کربو هیدارت ها با واحد گرم اندازه گیری کیلو کالری 4می شوند و هر گرم آنها ،
.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 ofpolyhydroxy (more than one -OH group) alcohols, orcompoundsThe term carbohydrate refers to hydrates of
carbon and isderived from the observation that the empirical
formulasfor these compounds contain approximately onemolecule 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:
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
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
DisaccharidesThree 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.
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
مولکول 20-3ترکیباتی هستند که دارای برای مثال :. مونوساکارید می باشند
رافینوز ، چغندرموجود در تری ساکارید ) می باشد.گاالکتوز+گلوکز+فروکتوز(
حبوبات و کدو موجود در تترا ساکارید ، گاالکتوز+گاالکتوز+گلوکز + ( استاکیوز
) می باشد.فروکتوز
Thanks