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Components of Food. Chemistry Project 2005-2006. Carbohydrates. Chemistry and Food. What is Carbohydrates ?. Compounds composed of carbon and water General formula C x H 2y O y H:O = 2 : 1 Divided into 3 types ---Monosaccharides ---Disaccharides ---Polysaccharides. Monosaccharides.

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Components of food

Components of Food

Chemistry Project 2005-2006



Chemistry and Food

What is carbohydrates
What is Carbohydrates ?

  • Compounds composed of carbon and water

  • General formula CxH2yOy

  • H:O = 2 : 1

  • Divided into 3 types

  • ---Monosaccharides

  • ---Disaccharides

  • ---Polysaccharides


  • Eg.---Glucose

  • Eg.---Fructose

  • Basic unit of carbohydrates

  • Sweet in taste, soluble in water

  • General formula C6H12O6


  • Formed from 2 monosaccharides

  • 2C6H12O6 -----C12H22O11 + H2O

  • Condensation




  • Condensation polymer of monosaccharides

  • nC6H12O6--(C6H10O5)n + n(H2O)

  • Condensation

  • Example:

  • ---Starch

  • ---Cellulose

Glycosidic linkage in carbohydrates
Glycosidic Linkage in Carbohydrates

  • Bond formed between 2 monosaccharides

  • Condensation---2 OH group

  • Removal of H2O

Hydrolysis of sucrose
Hydrolysis of Sucrose

  • Add water

  • 2 simple sugars

  • Dilute mineral acids

Hydrolysis of starch 1
Hydrolysis of starch (1)

  • With enzymes

  • To maltose

Hydrolysis of starch 2
Hydrolysis of Starch (2)

  • Boiled with dilute H2SO4

  • To glucose

  • (C6H10O5)n + nH2O-- nC6H12O6

Reducing and non reducing sugars
Reducing and Non-reducing Sugars

  • Reduces basic solution of Cu2+(aq)or Ag+(aq)

  • Sugar converted to acid

  • Aldehyde group

  • Keto group

Fehling’s test

Physical properties of proteins
Physical properties of proteins

  • Large Molecular mass ,typically several thousands.

    eg. hemoglobin :64 500

    viral proteins :40 000 000

  • Not truly soluble on water,but form colloidal suspension

  • Constituent element: C,H,O,N may contain S and P

  • Limitless type of protein

    e.g. E.coli :800 types

    human:10 000 types

Components of food

Components of food

Structure of amino acids

  • A group of over a hundred members

  • The commonest are the 20 essential ones,which cannot be synthesized by our bodies.While the rest are non-essential,and can be synthesized from the essential ones.

Components of food

Zwitterions formation

  • Basic amino group : -NH2

  • Acidic carboxyl group : -COOH

  • Neutral Amino Acid:

    no of amino group = no of carboxyl group

  • Basic Amino Acid:

    no of amino group > no of carboxyl group

  • Acidic Amino Acid:

    no of amino group < no of carboxyl group

Components of food

  • Dipolar : with both positive and negative pole

  • Form zwitterions

  • Soluble in water but not in organic solvent

  • Non-volatile, crystalline organic compound with high melting point

  • Amphoteric : with both acidic and alkaline properties


  • Biological significance : Constant Ph for enzymatic reaction

Components of food

Polypeptide Formation

  • Amino acid (condensation)dipeptidepolypeptide

Components of food

Structure of polypeptide

  • Three dimension

  • Four types of bonding:

    a) disulphide bond

    b) hydrogen bond

    c) hydrophobic interaction

    d) ionic bond (broken by alternation in pH)

Components of food


  • Change in shape but not the sequence

  • Factors:

    - Heat

    - Acid

    - Alkali

    - high electropositive eg.Ag+ Hg +

    - high electronegative eg. CN-

    - organic solvent

    - Mechanical force

Components of food

Function of proteins

1.cytoskeleton : cytoplasm consists of a network of fibrous


2. Membrane protein

3. Raw material for growth

4. Formation of enzymes, hormones, antibodies

5. Fibrous proteins for support and protection

6. Osmotic balance and buffering

7. Energy source

Components of food

Source of proteins

  • Egg

  • Milk

  • Daily products

  • Soya bean

  • meat

  • fish


Components of food

Site for protein digestion


Protease in gastric juice and pancreatic juice

Stomach & duodenum


Protease in intestinal juice


Amino Acid

Components of food

Absorption of amino acids

Amino acids

Capillaries in villi of small intestine


Components of food








Kidney for excretion

Components of food

Deficient disease


Symptoms of Kwashiorkor:

a) Inflammation of skin

b) Anaemia

c) Swelling of abdomen

Components of food

Test for Proteins

  • Protein Turns Yellow Albustix paper green

  • Biuret test:

  • Protein + NaOH + CuSO4  purple colouration

  • (blue)

  • Identification

  • Paper chomatography

  • 2 dimensioned 3 dimenstioned

What are fats and oils
What are fats and oils?

  • Fats and Oils are different lipids.

  • Lipids are rather diverse class of organic compounds of organic compounds that include triglycerides, phospholipids, steriods, etc.

  • insoluble in water, soluble in organic solvents.

  • They are mainly composed of C, H, O but with a very low proportion of oxygen in the molecules.

Structure of fats and oils
Structure of fats and oils:

  • Most natural fats and oils are mixed glycerides.

  • Glycerides are esters formed from propane-1,2,3-triol (glycerol) and a mixture of different long chain carboxylic acids.

  • The carboxylic acids(fatty acids) making up fats and oils are usually unbranched, having 14 to 18 carbons.

  • There are three ester groups per glycerol and the three R groups are usually different, fats and oils are often called triglycerides.

Components of food



A fatty acid

Animal fats and vegetable oils
Animal fats and Vegetable oils:

  • Fats and Oils are found in animals and plants.

  • Animal fats, such as lard and butter, are composed of glycerides rich in heavy chain, saturated fatty acids, Therefore they are solids at room temperatures.

  • Vegetable oils are liquids because of their high content of glycerides composed of light chain unsaturated fatty acids.

Hydrolytic and oxidative rancidity
Hydrolytic and Oxidative Rancidity

  • Fats and Oils develop an unpleasant smell if they are kept for too long.

  • They are liable to spoilage that produces an ‘off’ odour and a flavour described as rancidity.

  • Rancidity :

    -> (1) Hydrolytic (2) Oxidative

    -> Both of which release foul smelling aldehydes and carboxylic acids.

Hydrolytic rancidity
Hydrolytic rancidity

  • Presence of moisture in oils, which hydrolyzes the glyceride molecules into propane-1,2,3-triol and free carboxylic acids.

Components of food

  • This reaction is speeded up in the presence of certainmicro-organisms or in the presence of some enzymes.

  • Over a period of time, more molecules of carboxylic acids are liberated which may be volatile and have extremely unpleasant odours and flavours.

  • At room temperature, hydrolysis proceeds rapidly so that butter soon turns rancid.

  • So, to duel with, butter is usually covered and refrigerated.

Oxidative rancidity
Oxidative Rancidity

  • Oxidative spoilage occurs when fats/oils are exposed to air and undergo oxidation.

  • It results in the production of flavours such as ‘tallowy’,

    A taste of fatty according to “yahoo dictionary”.

  • Fats and oils with a high degree of unsaturation are more susceptible to oxidation.

  • The oxidation has a free radical mechanism and is accelerated by trace metals, light and free radical initiators.


  • It is flavourless and odourless

  • It easily decomposes to form highly reactive hydroperoxide free radicals


  • Can be contolled, But not be eliminated

  • Can be slow down by antioxidants.

  • Examples :

    butylated hydroxyanisole (BHA)

    butylated hydroxytoluene (BHT)

    carotene (Pro-Vitamin A)

    Vitamin E

Hydrolysis of fats and oils
Hydrolysis of Fats and oils

Hydrolysis is a chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water.

Fats can be hydrolysed into carboxylic acids and glycerol in an alkaline medium (NaOH).

It is a reversible reaction.

Hardening of unsaturated fat
Hardening of unsaturated fat

An unsaturated fat is a fat in which there is one or more double bond between carbon atoms of the fatty acid chain.

Such fat molecules are monounsaturated if each contains one double bond, and polyunsaturated if each contain more than one.

Unsaturated fat cannot pack together closely, because of their bent structure. As a result, unsaturated oils exist as a liquid at room temperature.


  • Hydrogenation is a chemical reaction which can convert an oil to a semisolid fat by adding hydrogen to some of the carboxylic acid C=C double bond , thus decreasing the degree of unsaturation.

  • As a result , they can pack together closer and has a higher melting point .

  • It is an important reaction to produce margarine.

  • Soft spread margarine are prepared by the catalytic partial hydrogenation of vegetable oil .

Catalytic hydrogenation
Catalytic Hydrogenation


  • An unsaturated fats

  • Solid forms of vegetable oil

  • Widely used as a substitute for butter

  • It is healthier than butter. (Why?)

    Use your brain to think…

  • Examples:

    Corn oil

    Soy bean oil

    Cottonseed oil

Iodine value
Iodine value:

Iodine value is used to measure the degree of unsaturation in fats and oils.

It is determined by reacting fats or oils with excess iodine which adds on across the double bonds in the carboxylic acid side chains .

The degree of unsaturation is defined as the number of grams of iodine needed to react with 100 grams of fats/oils.

The greater the value is , the greater the degree of unsaturation in the fat or oil.

Energy source
Energy Source

  • The energy yield of lipids is more than twice those of carbohydrates and proteins, as shown in the below table.

  • On average, around 20-30% of the daily energy requirement of the human body comes from oxidation of lipids

Energy reserve
Energy Reserve

Triglycerides are common energy reserve in the adipose tissue of animals. They are an excellent storage form of energy because of the followings:

  • They provide much more energy per gramme than carbohydrates and proteins.

  • They are insoluble in water so that they do not diffuse out of the cells and do not upset the osmotic balance of the cells.

  • They can be stored in the animal body in almost unlimited amount.

Component of cell membrane
Component of cell membrane

  • The cell membrane is formed by two layers (bilayers) of phospholipids, with the lipophilic hydrocarbon ends facing each other and the hydrophilic phosphate ends pointing outward to the aqueous environment.

  • Cholesterol in the cell membrane helps to limit the leakage of small molecules, and hold the hydrocarbon chains of the phospholipids together but not changing them into a solid form.

Regulatory components
Regulatory components

  • Cholesterol is also the precursor for the synthesis of steroid hormones. Some of them are sex hormones that stimulate the development and maintenance of secondary sexual characteristics.

  • Vitamin D, which regulates the absorption of calcium inside the intestine, is derived from cholesterol.

Component of digestive juice
Component of digestive juice

  • Bile salts are made in the liver with cholesterol as a raw materials. They emulsify dietary lipids into small oil droplets which increase the surface area for the enzymes to work.

Heat insulation
Heat insulation

  • Being a poor heat conductor, fats effectively reduce heat loss from the bodies of many animals, such as human beings, polar bears and penguins.


  • Fats, being soft, light and shock-absorbent, protect many internal organs such as the kidneys and the eyeball from the mechanical injury by cushioning them.

Oils on BunBun's face has protective function.


  • Ngo Yu Hin

  • Chung Man Chuen

  • Fung Ho On

  • Yim Pui Kin

  • Yeung Sheung Yai

  • Chan Kai Hung