Scope of Food Science ……..

10. Use of biotechnology in foods. • Pest and disease resistance

• Weed control

• Improve functionality

• Improve nutritional value

• Health foods

• Improve yield

11. Food Safety concerns: • Microbial safety

• Pesticide residues

• Industrial chemicals

• Genetically modified foods

Scope of Food Science ……..

12. National /International food standards to

promote and facilitate local /world food

trade

Constituents of Foods

• Foods are edible bio-chemicals from plants and

animals.

Major constituents in food: Carbohydrates

Proteins

Fats

and their derivatives

Constituents in Food ……..

• Minor constituents in food:

• inorganic substances - minerals

• organic substances:

• vitamins

• enzymes

• acids

• emulsifiers

• stabilizers

• oxidants and antioxidants

• pigments and colours

• flavors

Constituents in Food ……..

• In addition, a very important constituent, water,

is always present.

• Some food may contain substances that can be

toxic if consumed in large quantities.

• Above substances are arranged in different

foods to give their structure, texture, flavour,

color and nutritive properties.

• You may also find some constituents added to

food.

CARBOHYDRATES

• Contain the elements C, H and O.

• Hydrates of carbon

• Basic structure: Cx (H2O)y

• Types of carbohydrates:

– Sugars

– Starches

– Dextrins

– Cellulose

– Hemicellulose

– Pectins

– Gums

SUGARS

• The simplest carbohydrates.

Monosaccharides:

e.g. (i). Hexoses

(ii). Pentoses

Oligosaccharides:

• Consist of 2-9 sugar units

• Disaccharides are the most common and

important

Other oligosaccharides

Trisaccharides:

Raffinose: in beans

(galactose-glucose-fructose)

Maltotriose: (glucose-glucose-glucose)

Kestose: (glucose-fructose-fructose)

Tetrasaccharides:

Stachyose: in beans

(galactose-galactose-glucose-fructose)

Sesamose: (galact-galact-fructose-glucose)

SUGARS

Disaccharides:

• Formed by linking of two monosaccharide units

with splitting of a molecule of water.

E.g. Maltose (malt sugar) -

2 glucose units linked by α 1-4 linkage

Lactose (milk sugar) –

Glucose and galactose linked by α 1-4 linkage

Sucrose: (cane/ beet sugar) –

Glucose and fructose linked by α 1-2 linkage

SUGARS …….

Sugars differ in terms of solubility, sweetness

and rates of fermentation by microorganism etc.

Functional Properties of sugars:

Sweetness: Used as sweeteners in

confectionery

Solubility in water – form syrups

When water is evaporated from solution they

form crystals.

Sugars supply energy – 4 kcal/g

Functional Properties of Sugars …….

• They are readily fermented by microorganisms.

• Concentrated sugar solutions act as

preservatives

• Sugars are caramelized on heating. Caramel is

a food colourant and also flavouring agent.

• They contribute to browning reactions in food.

Reducing sugars react with amino acids and

form brown pigments (Maillard browning).

• They give body and mouthfeel to solutions in

addition to sweetness.

STARCH

• Starch is a polysaccharide. The repeating unit

of starch is α-D glucose.

• Starch consists of two fractions: amylose and

amylopectin.

• Amylose is unbranched while amylopectin is

branched.

• Amylose has α-1-4 linkages only. Amylopectin

has α-1-4 and α-1-6 linkages.

• Starch of food is primarily of plant origin.

Functional Properties of Starch

1. Relatively insoluble in cold water

2. Form pastes and gels in hot water

3. A good source of energy.

4. Occur in seeds and tubers as characteristic

starch granules.

5. When an aqueous suspension of starch is

heated the granules swell due to water uptake

and then ruptured.

Size and shape of starch granules

Functional Properties of Starch ……

6. The resulting viscous liquid is called a paste

and upon cooling it forms a gel

7. This process is known as gelatinization

8. Starch pastes are used to thicken foods

9. Starch gels are used in puddings.

10.Reactive groups of long chain sugar polymers

can be combined and aligned in a cross-linking

fashion to form fibres and films (Edible films

from starch – a unique coating and packaging

material).

Functional Properties of Starch ……

11. Partial breakdown of starch yields dextrin, which

are intermediate in chain length between starch

and sugars.

Gelatinization of starch:

• Starch molecule has hydrophilic groups and they

absorb water.

• The moisture content of cereal starch is about 12-

14%.

– Cold water can penetrate into the granule without

disturbing the granular structure. A maximum

water content of about 30% can be reached by

this means.

Gelatinizations of Starch

• When moisture absorbed starch granules are heated

they begin to swell rapidly.

• Further heating causes more absorption of water and

the granular structure collapses.

• The temperature at which this occurs is called the

gelatinization temperature.

• Gel formation:

• When a thick starch mixture is allowed to stand a firm

structure known as gel is formed.

Retrogradation of Starch

• The change of the starch gel into an insoluble

form (needle like crystals) upon freezing or

ageing, causing changes in food texture.

• These crystals are not identical to starch

granules.

• Retrogradation is the basis of staling of bread.

• Modified Starches:

• Properties of natural starch can be modified by

physical, chemical and/or enzymatic means.

Retrogradation of Starch ……

• This has greatly increased the range of uses

for starch as a food ingredient.

• (Controlling texture, desired viscosity with

minimum heating etc.)

• Sago is a modified starch.

Modification techniques:

1. Reduction of starch’s viscosity by chemically

or enzymatically breaking the molecules at the

glycosidic linkages.

2. Oxidation of some hydroxyl groups.

Modification techniques ……

3. Cross linking of hydroxyl groups on adjacent

starch molecules to form chemical bridges

between linear chains (to reduce swelling

when heated in water, withstand viscosity

under high temperature and acidity).

4. Reacting hydroxyl groups with a range of

reagents to form ester, ether, acetal and other

derivatives (reduce retrogradation on ageing

or freezing).

Types of modified starches

1. Pre-gelatinized starches:

Readily disperse in cold water and form

moderately stable suspensions.

2. Acid-modified starches:

Form gels of greater strength; Prevent large

viscosity increases upon heating.

3. Oxidized starches (Thin boiling starches):

Gel is less firm; gives low viscosity.

4. Cross-linked starches:

Stable to acid and high temperature during

cooking and canning.

Cellulose

• Basic structural material in the cell walls of plant

tissues.

• Carbohydrate polymers relatively resistant to

breakdown.

• Cellulose is a linear polymer of D-glucose units;

linkage: β-1-4 glucosidic bond.

• Repeating disaccharide unit of cellulose is

cellobiose.

Functional properties of Cellulose

• Cellulose is insoluble in cold and hot water and

is not digested by man.

• Cellulose is important, however, as a source of

dietary fibre.

• Long cellulose chains may be held together in

bundles forming fibres. E.g. cotton, lettuce,

celery

• Cellulose from plants and waste paper can be

enzymatically converted to glucose.

Functional properties of Cellulose….

• Supplied with a source of nitrogen and using

microorganisms, can be converted to single cell

protein (SCP), used for animal or human food.

• Derivatives of cellulose are widely used in food

industry. The most widely used derivative is

carboxymethyl cellulose (CMC).

• Addition of CMC prevents casein or soy protein

from precipitating at its isoelectric pH.

• CMC is used in ice cream industry to decrease

the mobility of water and thereby to contribute

to the smooth texture.

Hemicellulose

• Found in plant kingdom in association with cellulose.

• Large number of polysaccharides comes under the term

hemicellulose. E.g. xylan, glucan, mannans, xyloglucan,

arabinoxylan, glucomannan, galactomannan,

galactoglucomannan, glucuronoxylan

• They are made out of pentoses and hexoses. They may

contain either pentose or hexose, both of them or their

derivatives (heteropolysaccharide).

• Hemicellulose contains shorter chains (500-3000 sugar

units) compared to cellulose (7000-15000 glucose units

per polymer).

• Hemicellulose is branched while cellulose is not so.

• Hemicelluloses are bonded to cellulose and lignin in cell

walls, and have lesser strength compared to cellulose.

Functional properties of hemicellulose

• Generally they are insoluble in cold and hot water but

soluble in dilute acid and alkali solutions.

• The hemicelluloses containing acids in their side

chains are slightly charged, water soluble, and form

viscous gels.

• Like cellulose they also contribute to the fibre fraction

of food.

• They influence the baking characteristics of the flour.

Pectins

• Pectins are found in fruits and vegetables and are

gumlike. They are found in and between cell walls and

help hold the plant cells together.

• Like starches and celluloses, pectins are made up of

chains of repeating units, but the units are sugar acids

rather than simple sugars.

• The basic structure of pectins is made up of D-

galactouronic acid units linked together by α-1-4

linkages.

• Pectins are used in the manufacture of jams and jellies.

Pectins • About 80% of COOH groups of pectins are esterified with

methanol in natural pectins.

• The ratio of esterified- to non-esterified galactouronic acid

units determine the behaviour of pectin in food

applications (HM-pectin [DE>50%] Vs LM-pectin [DE<50%])

• The basis of gel formation is also different in both types

of pectin. HM pectin requires a high soluble solid content

(sugar) and a low pH (2.8-3.6) to form a gel.

• LM-pectin generally needs Ca to form a gel. Ionic brides

are formed between Ca and ionized COOH groups of

galactouronic acid. They can form a gel at a low sugar

content and higher pH values.

Functional properties of Pectins

• Pectins are soluble in water, especially in hot water.

• They contribute viscosity to tomato paste.

• They can be used as stabilizers in colloidal juices;

can stabilize the fine particles in orange juice from

settling out.

• Their gel-forming ability is widely used in the food

technology. Pectin in solution form gels when sugar

and acids are added and this is the basis of jam and

jelly manufacture.

• Pectin can be added to foods as thickeners.

Carbohydrate Gums

• These are substances with gummy

characteristics.

• Most of them are polysaccharides with hydrophilic

properties.

• Starches, pectin and derivatives of cellulose also

act like gums.

• Other carbohydrate gums from plants include

seed gums, plant exudate gums and seaweed

gums.

Carbohydrate Gums

Seed Gums:

Locust bean gum, Guar gum

Plant Exudate Gums:

Gum arabic, Gum karaya, Gum tragacanth

Seaweed Gums:

Agar-agar, Carageenan, Algin

Functional properties of Food Gums

• They are hydrocolloids. Used to improve water retention

in ice cream, gelled desserts and salad dressings.

• They improve textural properties in ice cream.

• Pectins are readily rehydratable.

• They may function as thickener in gravies or sauces.

• Used as an emulsion stabilizer in salad dressings.

• Act as protective colloid in chocolate milk and syrups.

• Used as flavour fixing agents and lubricants in extruded

foods.