Transcript Carbohydrates

B.SC Ist SEMESTER
INTRODUCTION TO FOOD AND NUTRITION
INTRODUCTION
CARBOHYDRATES:
A carbohydrate is a biological molecule consisting of carbon (C),
hydrogen (H) and oxygen (O) atoms, usually with hydrogen: oxygen
atom ratio of 2:1 (as in water).
Carbohydrates are one of the main types of nutrients. They are the most
important source of energy for your body. Your digestive system changes
carbohydrates into glucose (blood sugar). Your body uses this sugar for
energy for your cells, tissues and organs.
SOURCES
CHO
•FREE SUGARS
Monosaccharide
glucose
fructose
Disaccharides
sucrose
lactose
Sugar alcohols
sorbitol
•Polysaccharides
Digestible
Rapidly digestible starch
Slowly digestible starch
Resistance starch
Physically inaccessible
Resistant granules
retrograded amylase
Indigestible
cellulose
Hemicelluloses
SOURCES
fruit
fruit
cane & beet sugars
milk & milk product
cherries
processed food
legumes , pasta
whole grain
unpripre banana
cooked starch
bran
stalks & leaves of veg, outer covering of seed
FUNCTIONS OF CARBOHYDRATES
•SOURCES OF ENERGY : Carbohydrates are least expensive source of energy to the
body. Every grounds of carbohydrates, sugar or starch when oxidized yields on an average 4
Kilo calories. Since Indians consume large quantity of cereals, most of the requirement of
energy is met by carbohydrates.
•PROTEIN SPARING ACTION : The body uses carbohydrates as a source of energy,
when they are adequately supplied in the diet, sparing protein for tissue building. If diet
does not supply adequate calories from carbohydrates, the dietary is oxidized as a source of
energy.
•OXIDATION OF FATS : In oxidation of fats the acetyl CoA formed from the oxidation of
fatty acids reacts with oxaloacetic acid from carbohydrates and amino acid metabolism to
form citric acid which is oxidized for the TCA cycle back to the oxaloacetic acid through a
series of reaction.
•INDISPENSABILITY FOR NERVOUS SYSTEM: The main source of energy for
central nervous is glucose. Prolonged hypoglycemia can lead to irreversible damage to the
brain tissue.
•ROLE IN MUSCLE : Carbohydrates are the major source of energy for muscular work.
During muscular contraction, glycogen is broken down to lactic acid through glycolysis.
During the recovery period, lactic acid is first oxidized to pyruvic acid and acetyl CoA
which is then oxidised to CO2and H2O, thus producing energy for muscular work.
•ROLE IN LIVER : These include detoxifying action and regulating influence of protein and fats
metabolism. Liver is rich in glycogen and is more resistant to certain poison such as carbon tetra
chloride, alcohol, aesenic and toxins of bacteria. The rate of oxidation of amino acid in liver is
diminished if abundant supply of carbohydrates are available.
•SOURCE OF ENERGY FOR HEART MUSCLE : The heart muscle is mainly uses glucose as
source of energy. In hypoglycemia a definite adverse change in the working of the heart has been
observed.
•SYNTHESIS OF RIBOSE FROM GLUCOSE : The pentose ribose is present in RNA and in
many nucleotides. It is formed in the body from glucose by Hexose Mono Phosphate pathway.
•CONVERSION TO FAT : Excess of calories fed in diet in the form of carbohydrate is stored as
fat in adipose tissue. When the body is in need of energy it can be realized from the adipose tissue.
•PROMOTES GROWTH OF DESIRABLE BACTERIA : Lactose has several functions in the
gastrointestinal tract. It promotes the growth of desirable bacteria, some of which are useful in the
synthesis of B-complex vitamins. Lactose also enhances the absorption of calcium.
•CONTRIBUTION OF DIETARY FIBRE : A small amount of energy is produced from the
release of short chain fatty acids in the large intestine. Fiber stimulates the peristaltic movement. It
helps in preventing many degenerative disease.
•BIOSYNTHESIS OF AMINO ACIDS : The carbon skeleton for the synthesis of alanine, aspartic
acid and glutamic acid are provided by glucose during its oxidation, from pyruvic acid, oxale acetic
acid and α-ketoglutaric acid respectively.
•STRUCTURAL COMPONENT : Carbohydrates are precursors for many organic compounds. As
glycoproteins and glycolipids participate in the structure of cell membrane and cellular functions
such as cell growth adhesion and fertilization.
RECOMMENDED ALLOWANCES AND REQUIREMENT OF
CARBOHYDRATE
• CHO usually supply the largest proportion of energy to the body. Any
excess of CHO is converted by the body into fat & stored in tissue.
• CHO should be eaten only in sufficient quantity to satisfy hunger ,
after the need for other nutrition in the diet is satisfied.
• The minimum requirement of CHO is 100g. This is desirable to
prevent ketosis.
• However in a balanced diet 60% of total calories is recommended for
CHO. In a 2000 kcal diet 275-300g of CHO is recommended, only
10% should be from sugar & rest should come from complex CHO.
•A general recommendation of most dietary guidelines suggests that
complex carbohydrates and simpler carbohydrates, which are
“nutrition rich”, should make up the majority of carbohydrate
consumption. Examples are fruits (glucose and fructose), milk, and
milk products (lactose)
IMPORTANCE OF LACTOSE
LACTOSE
•Lactose is a milk sugar and is made exclusively in mammary gland of most
lactating animals and is very important.
•Lactose is less soluble than other disaccharides and is only 1/6 as sweet as
glucose.
•Lactose a disaccharide plays a great role. In absence of lactose in human body,
person suffer from lactose intolerance problem.
•This problem occurs as most of mammals do not consume milk after weaning
and mainly lactose intolerance is caused by deficiency of enzyme lactase which
hydrolyze lactose.
•In absence of this enzyme, lactose is not hydrolyzed into glucose and galactose
and these disaccharide's remain in gut for some time and act osmotically.
•Due to this, colonic bacteria ferment undigested lactose generating short chain
fatty acid, carbon dioxide, hydrogen which results in bloating, diarrhoea, and
other intestinal problems.
•Hence we can say lactose is very important in our life, if lactose is not present
it can lead to no. of problems as mentioned above.
IMPORTANCE OF STARCHStarch is a storage form of carbohydrate in plant and is a great contributor to
energy content of diet.
Starch is of great importance. When starch is cooked in moist heat, starch granules absorb water and swell
up and the cell wall gets rupture thus more accessible to digestive enzymes, due to
this food can be easily digested. Plant stores carbohydrates in the form of starch .
Cereals grains ,seeds, roots like potato contains a considerable amount of starch .
Maize starch and corn flour are better “thickening agent” than rice or wheat
starch. All starch are broken down into glucose in the digestive system.
 It is the storage form of carbohydrates in plants and comprised the primary
source of energy in the diet.
Cereals, grains, seeds, tubers such as potatoes contain large quantities of starch.
Starch on partial hydrolysis gives dextrin.
Starch consist of two polysaccharides components water soluble amylose {1520%} and a water insoluble amylopectin{80-85%}.