Scope of Food Science
Transcript of Scope of Food Science
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.
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.