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