Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen that provide energy. They are classified as monosaccharides, oligosaccharides, or polysaccharides based on their size. The main carbohydrates in food are starch, sucrose, lactose, and fiber. Carbohydrates are important for energy, structure, nutrient storage, and have many health benefits, but excess sugar intake can lead to issues like tooth decay, obesity, and diabetes.

1. CARBOHYDRATES
Sanjogta Thapa Magar
Food microbiology 3rd
sem

2. Introduction
Carbohydrates are defined as the as polyhydroxy aldehyde, ketones or acids and
their derivatives or compounds that yield these derivatives on hydrolysis.
Carbohydrates are the most abundant organic molecules in nature.
They are primarily composed of the elements carbon, hydrogen and oxygen.
Carbohydrates are one of the three major macronutrients found in food.
The formulas of many carbohydrates can be written as Cn(H2O)n.
The carbohydrates are a major source of metabolic energy, both for plants and for
animals that depend on plants for food

3. CLASSIFICATION OF CARBOHYDRATES

5. Monosaccharides
 They are simple sugars, or the compounds which possess a free aldehyde (CHO)
or ketone (C=O) group and two or more hydroxyl (OH) groups.
 They are the simplest sugars and cannot be hydrolysed further into smaller units.
 Monosaccharides contain a single carbon chain and are classified on the basis of
number of carbon atoms they possess, and as aldoses or ketoses depending upon
their groups.
 Aldoses : When the functional group carbonyl (CHO) in monosaccharides is
an aldehyde are known as aldoses e.g. Glyceraldehyde, glucose.
Ketoses : When the functional group carbonyl(C=O) is a keto group, they are
referred to as ketoses e.g. dihydroxyacetone, fructose.

7. Oligosaccharides
 These are compound sugars that yield 2 to 10 molecules of the same or different
monosaccharides on hydrolysis.
 Accordingly, an oligosaccharide yielding 2 molecules of monosaccharide on
hydrolysis is designated as a disaccharide, and the one yielding 3 molecules of
monosaccharide as a trisaccharide and so on.
 Disaccharides – Sucrose, Lactose, Maltose, Cellobiose, Trehalose, Gentiobiose,
Melibiose Trisaccharides – Rhamninose, Gentianose, Raffinose (= Melitose),
Rabinose, Melezitose Tetrasaccharides – Stachyose, Scorodose Pentasaccharide –
Verbascose

8. Disaccharides –
 Composed of 2 monosaccharides – cells can make disaccharides by joining two
monosaccharides by biosynthesis.
 Glucose + fructose = sucrose
• Table sugar.
• Found naturally in plants: sugar cane, sugar beets, honey, maple syrup
• Sucrose may be purified from plant sources into Brown, White and Powdered
Sugars.
 Glucose + galactose = lactose
• The primary sugar in milk and milk products.
• Many people have problems digesting large amounts of lactose (lactose intolerance)
 Glucose + glucose = Maltose
• Produced when starch breaks down. During germination of barley seeds, starch goes
through hydrolysis to form maltose.
• Used naturally in fermentation reactions of alcohol and beer manufacturing

9.  Among the oligosaccharides, disaccharides are the most common.
a disaccharide consists of two monosaccharide units (similar or dissimilar)
held together by a glycosidic bond.
 they are crystalline, water-soluble and sweet to taste.
 The disaccharides are of two types
1.Reducing disaccharides with free aldehyde or keto group e.g. maltose,
lactose.
2. Non-reducing disaccharides with no free aldehyde or keto group e.g.
sucrose, trehalose.

11.  Polysaccharides are polymers Containing 10 or more monosaccharide units
attached together.
 They are usually tasteless (non-sugars) and form colloids with water.
 They consist of repeat units of monosaccharides or their derivatives, held
together by glycosidic bonds.
 They are primarily concerned with two important functions-structural, and
storage of energy.
 Polysaccharides are linear as well as branched polymers.
 Examples:
1. Starch- digestible
2. Glycogen- digestible
3. Fiber- indigestible
• Cellulose gives structure to plants, fiber to our diet
• Glycogen is an energy storage sugar produced by animals
• Liver cells synthesize glycogen after a meal to maintain blood glucose levels

12.  Chemically, the polysaccharides may be distinguished into
• homopolysaccharides, which yield, on hydrolysis, a single monosaccharide
and
• heteropolysaccharides ,which produce a mixture of monosaccharides on
hydrolysis.
 Based on their functional aspect, the polysaccharides may be
grouped under two heads :
(a) Nutrient (or digestible) polysaccharides. These act as metabolic reserve of
monosaccharides in plants and animals.
e.g., starch, glycogen and inulin.
(b) Structural (or indigestible) polysaccharides. These serve as rigid mechanical
structures in plants and animals,
e.g.,cellulose, pectin and chitin and also hyaluronic acid and chondroitin

13. TYPES OF CARBOHYDRATESIN FOOD
Three main types :
• starch (complex carbohydrates)
• sucrose
• lactose
• fiber
Starch
 The major digestible polysaccharide in our diet.
 The storage form of carbohydrate in plants.
 Sources: Wheat, rice, corn, rye, barley, potatoes, tubers, yams, etc.
 Two types of plant starch:
1. Amylose
2. Amylopectin

14. 1. Amylose: is in the form of straight chain linked together with α- 1-
4,linkages indicating 300 – 5,500 glucose units per molecules, molecular
wt range from 105 to 106. Generally it is water soluble and gives blue
colour with iodine.
2. Amylopectins: It contain beside straight chain several branched chains,
which are arranged in α—1-4 and β-1-6 linkage units, one molecule of
amylopectin contains 50,000 to 5,00,000 glucose molecules, molecular wt.
range from 107 to 108, it is insoluble in water and gives purple colour with
iodine .

16. Sucrose
 Sucrose (cane sugar) is the sugar of commerce, mostly produced by sugar
cane.
 Sucrose is made up of α-D-glucose and β-D-fructose.
 The two monosaccharides are held together by a glycosidic bond (α1-β2),
between C1 of α-glucose and C2 of β-fructose.
 The reducing groups of glucose and fructose are binvolved in glycosidic bond,
hence sucrose is a non-reducing sugar.
 Sucrose is the major carbohydrate produced in photosynthesis.

17. Lactose
 Lactose is more commonlv known as milk sugar since it is the disaccharide
found in milk.
 Lactose is composed of β-D-galactose and β-D-glucose held together by β(1-4)
glycosidicbond.
 The anomeric carbon of C1 glucose is free, hence lactose exhibits reducing
properties.
 Lactose of milk is the most important carbohydrate in the nutrition of young
mammals.
 It is hydrolysed by the intestinal enzyme lactase to glucose and galactose.

18. Cellulose
 Cellulose occurs exclusively in plants and it is the most abundant
organic substance in plant kingdom.
 lt is a predominant constituent of plant cell wall.
 Cellulose is totally absent in animal body.
 Cellulose is composed of β-D-glucose units linked by β(1-4)
glycosidic bonds.
 Cellulose cannot be digested by mammals including man-due to
lack of the enzyme that cleaves β-glycosidic bonds (a amylase
breaks α bonds only).
 Certain ruminants and herbivorous animals contain microorganisms
in the gut which produce enzymes that can cleave β-glycosidic
bonds.
 Cellulose, though not digested, has great importance in human
nutrition.

19.  lt is a major constituent of fiber, the non-digestable carbohydrate.
 The functions of dietary fiber include decreasing the absorption of
glucose and cholesterol from the intestine.

21. FLAVOUR & COLOUR PRODUCTION BY CARBOHYDRATES
 Flavor & color reactions of carbohydrate constituents of foods may be
classified into:
Enzymatic browning reactions
Caramelization
Maillard reaction
Strecker degradation

22. 1
•Part of natural process of decay
•When food substances are deprived of the protection of water, they get oxidized
or chemically dehydrated to reactive intermediates, which polymerize to dull,
brown, humic substances.
•Two types:
Oxidative Browning:
 Oxidases are active & convert functional groups to reactive carbonyl
compounds which undergo further non-enzymatic oxidative browning
reactions.
Non-oxidative Browning:
 Glycosyl hydrolases initiate non-oxidative browning in natural products by the
release of reducing sugars.
 It is important in color & flavor development in dates,honey, maple syrup,
chocolate & vanilla processing.
 Reducing sugars undergo a series of reactions even in the absence of oxygen or
other oxidants to yield reactive carbonyl compounds.

23. •Involves a complex group of reactions that are the result of direct heating
of carbohydrates.
•Heat hastens the inversion of sucrose to yield reducing sugars which
condense to higher oligosaccharide & dextrins.
•When amino acids do not participate in the heat induced reactions, the
complex color & flavor forming reactions of carbohydrates are called
caramelization reactions.
•Brown pigments that characterize caramel & other foods are due to HMF
& its precursors.
•Three commercial types of caramel colors:
i. Acid fast caramel used in cola drinks, made using ammonium
bisulphite catalyst.
ii. Brewer’s color found in beer, made form sucrose in the presence of
ammonium ions.
iii. Baker’s color in baked goods, results from direct pyrolysis of sucrose
to give burnt sugar color.

24. •In the presence of amino compounds, the browning of sugars occurs more rapidly,
particularly in neutral or alkaline conditions in a sequence of reactions called
Maillard reaction.
•Browning & aroma formation during cooking, frying, baking or roasting are
caused by this reaction.
•Lysine is the most reactive amino acid followed by met, arg, trp & his.
•Chemical Mechanism:
-Carbonyl group of sugar reacts with amino group of the amino acid producing N
substituted glycosylamine & water.
-Unstable glycosylamine undergoes Amadori rearrangement, forming ketosamines.
-

25. •Involves transamination & decarboxylation reactions.
•It is the interaction of α-dicarbonyl compounds with α-amino acids at
elevated temperature.
•The reaction yields aldehydes, aminoketones & CO2.
•These aldehydes contribute to fruity, ester-like, malty green or honey like
aromas in foods.
•Aminoketones formed undergoes further reactions to yield pyrazine
derivatives. These compounds together with products obtained from
dimerization of sugar residues make a major contribution to the characteristic
aroma of baking.

26. Function and health benefits of carbohydrates
 The most abundant dietary source of energy(4.1kcal/g)
 Precursors for many organic compound i.e. fats, amino acids etc.
 Structural components such as cellulose of plants, exo-skeleton(chitin) of insects:
contains cell wall of microorganism(n-acetyl glucosamine and n-acetyl muramic
acid), ground substances of cartilage and bone i.e. synovial fluid contains
hyaluronic acid which helps in lubrications, promotes wound healing, shock
absorber
 Are glycoproteins and glycolipid participate in structure of cell membrane and
cell function such as cell growth, adhesion and fertilization(i.e. follicles
stimulating hormones(FSH), leutinizing hormones(LH), thyroid stimulating
hormone(TSH), lacta-albumin (glycoprotein)
 Every cell carbohydrates on its surface which help to recognize other substance.
In gram negative bacteria, the outer membrane is made up of LPS, which is again
composed of core polysaccharides and O-antigens. Polysaccharides contain diff
sugar which confers cell specificity
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27.  Also serves as the storage from of energy(i.e. glycogen in animal and starch
in plants) to meet the immediate energy demands
 Plays an important role in defense mechanism.ie. Immunoglobins formed
in response to the antigens in the body.
 Heparin is polysaccharide in our body prevents clotting in the bloodstream
 Osmotic regulation
 Blood grouping is based on the carbohydrates molecule ABO blood
markers of blood(RBC) which is clinically very important to distinguish
blood type & during blood transfusion
 Improve immune system function
 Streptomycin is a glycoside employed in the treatment of tuberculosis
 Contain keratin sulfate( glycosaminoglycan) keeps cornea transparent.
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28. fibers
 Soluble fiber(oligosaccharides), viscous, fermentable
Easily digested by bacteria in colon, hence enhances the health of large
intestine. Associated with protection against heart disease and diabetes
Lower cholesterol by binding the bile and slow glucose absorption
Improve glucose metabolism
 Insoluble fibers(polysaccharides) and not easily fermented
Promote bowel movements
Alleviate constipation by holding moisture in stool, softening them, speed
fecal passage through colon
 Reduces the risk of type 2 diabetes by improving the sensitivity of insulin
 also can promote weight loss
 Lower risk of diverticulosis, hemorrhoids and appendicitis
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29. Carbohydrates found in food
Sweeteners
Whole foods that act as natural sweeteners are the richest sources of the
monosaccharides fructose and glucose, usually in combination. In addition to
table sugar, which is made from either cane or beets, natural sweeteners
such as honey and molasses are high in simple sugars. Honey is mostly
fructose. Corn syrup -- the regular kind, not high-fructose -- and maple syrup
are mostly glucose.
Fruits
Fruits, especially apples, cherries, grapes, guavas, lichees, honeydew melon,
watermelon, mangoes, papayas, pears, persimmons and pineapple, are the
richest whole-food sources of the monosaccharide fructose. simple sugars
from whole fruits, which contain fiber that slows down body’s absorption of
sugars, as well as healthful vitamins, minerals and antioxidants. Dried fruits
and fruit juices are more concentrated sources of fructose.
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30. Dairy Products and Meat
Dairy products are the richest food sources of galactose. Milk, butter, sour
cream, ice cream, yogurt and other dairy products don’t contain actual
galactose, but they do have a sugar called lactose, which the body breaks
down into glucose and galactose. Ingredients derived from dairy products,
such as whey protein, dry milk solids and casein, can also contribute
galactose . While meats generally contribute little in the way of sugars, organ
meats such as liver are the exception. They’re rich in galactose.
Vegetables and Legumes
Generally, vegetables contain much less sugar than fruits, and don’t
contribute many simple sugars to the diet. Vegetables that tend to contain
more fructose and soluble and insoluble fibers include asparagus, beans,
broccoli, cabbage, onions and leeks, peanuts, tomatoes and zucchini. Beans,
lentils, chickpeas and sugar beets also provide galactose
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31. HEALTH PROBLEMS
 Excess of sugar leads to nutrient deficiency and tooth decay
 Consuming high amount of sucrose or fructose may cause obesity by
supply calories
 Diabetes: after food intake, blood glucose rises and is not regulated
because of inadequate insulin. These high glucose levels are believed to be
at least one cause of the serious long-term consequences of untreated
diabetes—kidney failure, cardiovascular disease, blindness, and impaired
wound healing
 Hypoglycemia: blood glucose drops dramatically, too much insulin, activity
inadequate food intake, illness
 Lactose intolerance: an intolerance to lactose can occur in people who
inherit or lose the ability to produce the enzyme lactase that hydrolyses
lactose into its monosaccharide units leads to diarrhea and flatulence
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32. HEALTH PROBLEMS
 Galatosemia: failure in converting glucose to galactose
 Glycogen storage disease
 Glucose is the principal fuel for the brain. When the amount of glucose
reaching the brain is too low, the consequences can be dire: lethargy,
coma, permanent brain damage, and death
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