Transcript Protein Foods

Food Biotechnology
Dr. Kamal E. M. Elkahlout
Food Biochemistry 3
Proteins
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Complex molecules widely distributed in all
food stuffs.
Every Protein has a unique structure and
confirmation or shape therefore carry out
specific functions.
All proteins are made up of amino acids.
PLANT SOURCES
ANIMAL SOURCES
Contain carbon ,hydrogen, oxygen and nitrogen . Some
also contain sulfur
 Each amino acid is compose of a carbon bonded to four
groups
 The other three
- a nitrogen group (-NH2) called an amino group
(or amine)
- an acid group (-COOH)
- a hydrogen (-H)
- R group – determines type and name of amino acid
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All protein
 amino acids joined
together by peptide
bond.
Dipeptide
 2 amino acids joined
together
Polypeptide
 several amino acids
joined together.
Conformation
 Primary
 Secondary
 Tertiary
 Quaternary
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Specific sequence of amino acid joined by
peptide bonds along the protein chain.
If one single amino acid in the chain was
changed it could completely alter the
structure and function of the protein
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Regular repeating structures
 beta pleated sheets
 alpha helix
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stabilized by hydrogen bonds between
groups in the main chain of the polypeptide.
The hydrogen bonds form between the
oxygen in the carboxyl group of one amino
acid and the hydrogen in the amino group of
another amino acid.
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Three dimensional organization of a complete
protein chain.
Spatial arrangement of a protein that contains
regions of a beta pleated sheets and alpha
helix.
Tertiary structure is build on the secondary
structure of a specific protein.
The intramolecular
bonds can include
 ionic bonds,
 hydrogen bonds,
 disulfide bonds (often
called bridges),
 and hydrophobic
interactions.
Two or more polypeptides linked together to form a
single protein.
 All types of bonding previously mentioned are
involved with quaternary proteins.
 Sometimes these proteins will contain a prosthetic
group, also known as a non-polypeptide structure.
 For example
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 in hemoglobin, the four polypeptides are linked to a heme
(haem) group which is not made up of amino acids.
 These proteins that contain a prosthetic group are often
referred to as conjugated proteins.
1. Amphoteric
 Able to act as acid or base.
 Enables them to resist small changes in pH.
 Buffering capacity
2. Isoelectric Point
 The pH at which the protein is electrically
neutral.
 The overall charge is neutral.
 At isoelectric point , protein molecules
precipitate as they carry no net charge.
 pH of isoelectric point differs for each protein.
 Important in food processing for cheese
production.
 Lactic acid is added to milk to bring ph to isoelectric
point of major milk protein (casein) – precipitate and
form curd.
3. Water Binding Capacity
 Water molecules can bind to the backbone and
to polar and side chains of a protein.
 Protein may bind varying amounts of water .
 Protein with many charged and polar groups bind
water rapidly.
 Proteins with many hydrophobic groups do not bind
much water.
 Protein close to isoelectric point bind less water.
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Presence of bound water helps to maintain the
stability of a protein dispersion.
4. Salting In and Salting Out
Some protein cannot be dispersed in pure water.
Readily dispersed in dilute salt solution.
Salting In
Salt solution increases the dispersibility of a
protein.
Brine injected into Ham to increase the
dispersibility of protein.
Increases water binding capacity thus Ham is
moister and weight is increased.
Poultry – polyphosphates are added.
Salting Out
 Occurs at high salt concentrations
 Salt competes with protein for water.
 Insufficient water available to bind to the
protein so protein precipitates.
 Not normally a problem in food processing .
 Contributing factor to deterioration of food
quality during freezing of food.
 During Freezing
 Water is effectively removed as ice crystals
 Concentration of liquid water decreases
 The solute concentration increases.
Change in structure of protein molecules.
The process results in the unfolding of molecules.
Factors which contribute to denaturation are
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heat,
salts,
pH
mechanical action.
Denaturation is a partially reversible change. For example, when an egg
white is whisked it incorporates air to form a foam.
If the foam is left to stand, it will
collapse back to form liquid
egg white.
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Coagulation follows denaturation.
Example,
 When egg white is cooked it
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changes colour and becomes firmer
or sets.
The heat causes egg proteins to
unfold from their coiled state and
form a solid stable network.
This change is irreversible.
Another form of coagulation occurs in the production of cheese.
Rennin (an enzyme from a calf’s stomach) is added to milk
causing the protein casein to clot, producing curds (solid) and
whey (liquid).
Other applications of coagulation are:
• yogurt production;
• thickening of sauces with beaten egg;
• binding ingredients together, e.g. fish, cakes,
reformed meats;
• providing a coating for products, e.g. scotch eggs.
Two proteins, gliadin and glutenin, found in wheat flour, form gluten
when mixed with water.
Gluten is strong, elastic and forms a 3D network in dough. In the
production of bread, kneading helps untangle the gluten strands
and align them.
Gluten helps give structure to the bread and keeps in the gases
that expand during cooking. The amount and type of protein
present depends on the flour type and quality. Strong flour
contains a maximum of 17% protein, plain flour 10%.
Products that require short or non-elastic textures, such as biscuits and
cakes, use flours with lower protein contents.
Gelatine is a protein which is extracted from collagen, present in
connective tissue in meat.
When it is mixed with warm water the gelatine protein
molecules start to unwind.
Although on cooling a stable network is formed, trapping the
liquid.
Gelation is reversible.
9. Hydrolysis of peptides and proteins
Breaking peptide bonds to form small peptide
chains
1. Acid digestion using concentrated acids.
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2.
Used mostly in research not in Food processigng.
Catalysed by proteolytic enzymes
Example 1 - (ficin, pappin and Bromelin)
 Used as meat tenderisers
Example 2 – Rennet
- Used to make curd which can be processed into
cheese
10. Maillard Browning
Non enzymatic browning.
Reaction responsible for brown color of baked
products.
Free carbonyl group of reducing sugar reacts
with a free amino group of protein
When heated the result is brown color
All enzymes are proteins.
Important In food processing as they catalyse
various reactions that affect
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Color
Flavour
Texture
Overall Quality of foods
Reactions may be desirable or undesirable.
Produce unwanted discoloration or off flavors in
foods
Functional Property
A characteristic of the protein that enables it to
perform a specific role or function in food.
Dependent on the amino acid composition and
sequence as they determine the
conformation and properties of the protein.
Whey Protein
 Solubility (does not precipitate at iselectric
point)
 Fortify acidic beverages (sports drinks)
 Nutritional fortifier in baked products.
Egg Proteins
 Thickening
 Binding
 Egg yolk – best emulsifying agent
 Egg White – best foaming agent
Gelatin and Egg White
 Gelling agents
 Egg whites upon heating form firm gell
(boiled egg)
 Gelatin used to make jelly and other
congealed products.
 Gells formed when protein molecules form 3D
network due to assiciation of hydrogen bonds.
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Protein Foods used in many foods to control
texture due to their ability to :
 Thicken
 Gel
 Emulsify
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Such food products must be processed,
handled and stored with care to ensure that
the proteins retain their functional
properties.