Transcript What Is Food Science? - NFSC Faculty Website

Proteins
From the Greek “proteios” or primary.
Properties of Amino Acids:
 Zwitterions
are electrically neutral, but carry a
“formal” positive or negative charge.
 Give proteins their water solubility
Shape Interactions of Proteins
Emulsoids and Suspensiods

Proteins should be thought of as solids

Not all in a true solution, but bond to a lot of water

Can be described in 2 ways:

Emulsoids- have close to the same surface
charge, with many “shells” of bound water

Suspensoids- colloidal particles that are
suspended by charge alone
Quick Application: Food Protein Systems
 Milk-
Emulsoid and suspensoid system
 Classified
as whey proteins and caseins
 Casein - a phosphoprotein in a micelle structure
 Suspensoid - coagulates at IEP (casein)
 Egg
(Albumen) – Emulsoid
 Surface
denatures very easily
 Heating drives off the structural water and creates a
strong protein to protein interaction
 Cannot make foam from severely denatured egg white,
requires bound water and native conformation
Functional Properties of Proteins
3 major categories
 Hydration properties

Protein to water interactions
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Structure formation
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Dispersion, solubility, adhesion, viscosity
Water holding capacity
Protein to protein interactions
Gel formation, precipitation, aggregation
Surface properties
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Protein to interface interactions
Foaming and emulsification
1. Hydration Properties (protein to water)

Most foods are hydrated to some extent.
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Behavior of proteins are influenced by the presence of water and
water activity
Dry proteins must be hydrated (food process or human digestion)

Solubility- as a rule of thumb, denatured proteins are less
soluble than native proteins
 Many proteins (particularly suspensoids) aggregate or
precipitate at their isoelectric point (IEP)
 Viscosity- viscosity is highly influenced by the size and
shape of dispersed proteins

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Influenced by pH
Swelling of proteins
Overall solubility of a protein
2. Structure Formation (protein to protein)

Gels - formation of a protein 3-D network is from a balance
between attractive and repulsive forces between adjacent
polypeptides
 Gelation- denatured proteins aggregate and form an ordered protein
matrix
 Plays major role in foods and water control
 Water absorption and thickening
 Formation of solid, visco-elastic gels
 In most cases, a thermal treatment is required followed by cooling


Yet a protein does not have to be soluble to form a gel (emulsoid)
Texturization – Proteins are responsible for the structure and
texture of many foods
 Meat, bread dough, gelatin
 Proteins can be “texturized” or modified to change their
functional properties (i.e. salts, acid/alkali, oxidants/reductants)

Can also be processed to mimic other proteins (i.e. surimi)
3. Surface Properties (protein to interface)

Emulsions- Ability for a protein to unfold (tertiary
denaturation) and expose hydrophobic sites that can
interact with lipids.
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Alters viscosity
Proteins must be “flexible”
Overall net charge and amino acid composition
Foams- dispersion of gas bubbles in a liquid or highly
viscous medium
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Solubility of the protein is critical; concentration
Bubble size (smaller is stronger)
Duration and intensity of agitation
Mild heat improves foaming; excessive heat destroys
Salt and lipids reduce foam stability
Some metal ions and sugar increase foam stability
Factors Affecting Changes to
Proteins
Denaturation
Aggregation
Salts
Gelation
Changes to Proteins

Native State
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The natural form of a protein from a food
The unique way the polypeptide chain is oriented
There is only 1 native state; but many altered states
The native state can be fragile to:
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Acids
Alkali
Salts
Heat
Alcohol
Pressure
Mixing (shear)
Oxidants (form bonds) and antioxidants (break bonds)
Changes to Proteins
 Denaturation
 Any
modification to the structural state
 The structure can be re-formed
 If severe, the denatured state is permanent
 Denatured
proteins are common in processed foods
 Decreased
water solubility (i.e. cheese, bread)
 Increased viscosity (fermented dairy products)
 Altered water-holding capacity
 Loss of enzyme activity
 Increased digestibility
Changes to Proteins

Temperature is the most common way to denature a
protein
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Both hot and cold conditions affect proteins
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Heating affects the tertiary structure
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Every tried to freeze milk? Eggs?
Mild heat can activate enzymes
Hydrogen and ionic bonds dissociate
 Hydrophobic regions are exposed
 Hydration increases, or entraps water
 Viscosity increases accordingly
Changes to Proteins
 We
discussed protein solubility characteristics
 Solubility depends on the nature of the solution
 Water-soluble proteins
generally have more polar
amino acids on their surface.
 Less soluble proteins have less polar amino acids
and/or functional groups on their surface.
Isoelectric Precipitations
 Proteins
---++
have no net charge at their IEP
----++
-++
--
++
++
++
++
++
++
Strong Repulsion
(net negative charge)
--
--
--
---
Aggregation
(net neutral charge)
Strong Repulsion
(net positive charge)
++
-++
++
++
++
--++
-++
++
++
Isoelectric Precipitations
 Proteins
--
---
--
--
--
Na+
can be “salted out”, adding charges
Na+
Na+
Aggregation
(net neutral charge)
++
++
++
++
++
++
ClCl-
Cl-
Measuring IEP Precipitations
 Empirical
measurements for precipitation
 A protein is dispersed in a buffered solution
 Add
salt at various concentrations
 Add alcohols (disrupt hydrophobic regions)
 Change the pH
 Add surfactant detergents (i.e. SDS)
 Centrifuge and
 The
measure quantitatively
pellet will be insoluble protein
 The supernatant will be soluble protein
Gel Formation

Many foods owe their physical properties to a gel
formation. Influences quality and perception.
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Cheese, fermented dairy, hotdogs, custards, etc
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As little as 1% protein may be needed to form a rigid gel
for a food.
 Most protein-based gels are thermally-induced
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Thermally irreversible gels are most common
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Cause water to be entrapped, and a gel-matrix formation
Gel formed during heating, maintained after cooling
Will not reform when re-heated and cooled
Thermally reversible gels
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Gel formed after heating/cooling. Added heat will melt the gel.
What is more important in foods?
Protein precipitation
or
Protein solubilization
???
Effects of Food Processing
Processing and Storage
 Decreases
 Loss
of nutritional value in some cases
 Severity
 Loss
spoilage of foods, increases shelf life
of processing
of functionality
 Denatured
 Both
proteins have far fewer functional aspects
desirable and undesirable flavor changes
Processing and Storage
 Proteins
are affected by
 Heat
 Extremes
in pH (remember the freezing example?)
 Oxidizing conditions
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Oxidizing additives, lipid oxidation, pro-oxidants
 Reactions
with reducing sugars in browning rxns
Processing and Storage
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Mild heat treatments (< 100°C)
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May slightly reduce protein solubility
Cause some denaturation
Can inactive some enzymes
Improves digestibility of some proteins
Severe heat treatments (for example: >100°C)
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Some sulfur amino acids are damaged
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Deamination can occur
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Release of hydrogen sulfide, etc (stinky)
Release of ammonia (stinky)
Very high temperatures (>180°C)
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Some of the roasted smells that occur with peanuts or coffee
Enzymes
A quick review, since we
know the basics already
Enzyme Influencing Factors

Enzymes are proteins that act as biological catalysts
 They are influenced in foods by:
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Temperature
pH
Water activity
Ionic strength (ie. Salt concentrations)
Presence of other agents in solution
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Metal chelators
Reducing agents
Other inhibitors
Also factors for
Inhibition, including:
Oxygen exclusion
and
Sulfites
Enzyme Influencing Factors

Temperature-dependence of enzymes
 Every enzyme has an optimal temperature for maximal
activity
 The rate/effectiveness of an enzyme: Enzyme activity
 For most enzymes, it is 30-40°C
 Many enzymes denature >45°C
 Each enzyme is different, and vary by isozymes
 Often an enzyme is at is maximal activity just before it
denatures at its maximum temperature
pH
 Like
temp, enzymes have an optimal pH where
they are maximally active
 Generally between pH 4 and 8
 with
 Most
many exceptions
have a very narrow pH range where they
show activity.
 This influences their selectivity and activity.
Water Activity
 Enzymes need free water to operate
 Low Aw foods have very slow enzyme reactions
Ionic Strength
 Some ions may be needed by active sites on the
protein
 Ions
may be a link between the enzyme and substrate
 Ions change the surface charge on the protein
 Ions may block, inhibit, or remove an inhibitor
 Others, enzyme-specific
Enzymes

Before a chemical reaction can occur, the activation energy (Ea)
barrier must be overcome
 Enzymes are biological catalysts, so they increase the rate of a
reaction by lowering Ea
Enzymes
The effect of temperature is two-fold

From about 20, to 35-40°C (for enzymes)
 From about 5-35°C for other reactions
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Q10-Principal: For every 10°C increase in temperature, the reaction rate will
double
Not an absolute “law” in science, but a general “rule of thumb”
At higher temperatures, some enzymes are much more stable than
other enzymes
Enzymes

Enzymes are sensitive to pH – most enzymes active only within a pH range of 34 units (catalase has max. activity between pH 3 & 10!)
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The optimum pH depends on the nature of the enzyme and reflects the
environmental conditions in which enzyme is normally active:
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Pepsin pH 2; Trypsin pH 8; Peroxidase pH 6
pH dependence is usually due to the presence of one or more charged AA at the
active site.
Nomenclature
Each enzyme can be described in 3 ways:
 Trivial name: -amylase
 Systematic name: -1,4-glucan-glucono-hydrolase
substrate

reaction
Number of the Enzyme Commission: E.C. 3.2.1.1
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3- hydrolases (class)
2- glucosidase (sub-class)
1- hydrolyzing O-glycosidic bond (sub-sub-class)
1- specific enzyme
Enzyme Class Characterizations
1.
Oxidoreductase
Oxidation/reduction reactions
2.
Transferase
Transfer of one molecule to another (i.e. functional groups)
3.
Hydrolase
Catalyze bond breaking using water (ie. protease, lipase)
4.
Lyase
Catalyze the formation of double bonds, often in
dehydration reations
5.
Isomerase
Catalyze intramolecular rearrangement of molecules
6.
Ligase
Catalyze covalent attachment of two substrate molecules
1. OXIDOREDUCTASES
Oxidation
Is
Losing electrons
Reduction
Is
Gaining electrons
Electron acceptor
eXm+
reduced
Xm2+
e-
oxidized
Electron donor
Redox active (Transition) metals
(copper/ iron containing proteins)
1. Oxidoreductases: GLUCOSE OXIDASE

-D-glucose: oxygen oxidoreductase

Catalyzes oxidation of glucose to glucono-  -lactone
-D-glucose
Glucose oxidase D glucono--lactone
FAD
H2O2
Catalase
FADH2
O2
+ H2 O
D Gluconic acid
H2O + ½ O2
Oxidation of glucose to gluconic acid
1. Oxidoreductases: Catalase
hydrogenperoxide: hydrogenperoxide oxidoreductase
 Catalyzes conversion of 2 molecules of H2O2 into
water and O2:
H2O2 -------------------
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H2O +1/2 O2
Uses H2O2
When coupled with glucose oxidase  the net result is
uptake of ½ O2 per molecule of glucose
Occurs in MO, plants, animals
1. Oxidoreductases: PEROXIDASE (POD)
donor: hydrogenperoxide oxidoreductase

Iron-containing enzyme. Has a heme
prosthetic group
N
N
Fe
N
N
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Thermo-resistant – denaturation at ~ 85oC

Since is thermoresistant - indicator of proper blanching
(no POD activity in blanched vegetables)
1. Oxidoreductases: POLYPHENOLOXIDASES (PPO)
Phenolases, PPO
 Copper-containing enzyme
 Oxidizes phenolic compounds to o-quinones:
 Catalyze conversion of mono-phenols to o-diphenols
 In all plants; high level in potato, mushrooms, apples, peaches,
bananas, tea leaves, coffee beans
Tea leaf tannins
Catechins
Procyanidins
Gallocatechins
Catechin gallates
PPO
O2
o-Quinone + H2O
Colored products
Action of PPO during tea fermentation; apple/banana browning
1. Oxidoreductases: LIPOXYGENASE
H
H
………
H
……..
C
C
C
C cis
cis
H
H
+ O2
H
H
H
C
H
C
C
C
cis
H
C
trans
……..
OOH
Oxidation of lipids with cis, cis groups to conjugated cis, trans hydroperoxides.
Enzymes !!!
 We
have observed carbohydrate hydrolysis
 Sucrose
into glu + fru
 Starch into dextrins, maltose, and glucose
 We
will observe lipid hydrolysis
 Break-down
of fats and oils
 Enzyme-derived changes
 So….the
enzyme discussion is not over yet.
Enzymes !!!
 We
have observed carbohydrate hydrolysis
 Sucrose
into glu + fru
 Starch into dextrins, maltose, and glucose
 We
will observe lipid hydrolysis
 Break-down
of fats and oils
 Enzyme-derived changes
 So….the
enzyme discussion is not over yet.
Worthington Enzyme Manual
http://www.worthingtonbiochem.com/index/manual.html
IUPAC-IUBMB-JCBN
http://www.chem.qmul.ac.uk/iubmb/enzyme
Lipids
Lipids
Main functions of lipids in foods
 Energy and maintain human health
 Influence on food flavor
 Fatty
acids impart flavor
 Lipids carry flavors/nutrients
 Influence on
 Solids
food texture
or liquids at room temperature
 Change with changing temperature
 Participation in emulsions
Lipids
 Lipids
are soluble in many organic solvents
 Ethers
(n-alkanes)
 Alcohols
 Benzene
 DMSO (dimethyl sulfoxide)
 They
are generally NOT soluble in water
 C, H, O and sometimes P, N, S
Lipids

Neutral Lipids
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
Waxes
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Long-chain alcohols (20+ carbons in length)
Cholesterol esters
Vitamin A esters
Vitamin D esters
Conjugated Lipids


Triacylglycerols
Phospholipids, glycolipids, sulfolipids
“Derived” Lipids


Fatty acids, fatty alcohols/aldehydes, hydrocarbons
Fat-soluble vitamins
Lipids
Structure
 Triglycerides or triacylglycerols
 Glycerol + 3 fatty acids
 >20 different fatty acids
Lipids 101-What are we talking about?
 Fatty
acids- the building block of fats
 A fat with no double bonds in it’s structure is said to
be “saturated” (with hydrogen)
 Fats with double bonds are referred to as mono-, di-,
or tri- Unsaturated, referring to the number of
double bonds. Some fish oils may have 4 or 5
double bonds (polyunsat).
 Fats are named based on carbon number and number
of double bonds (16:0, 16:1, 18:2 etc)
Lipids
liquid triacylglycerides “Oleins”
 Fat- solid or semi-solid mixtures of crystalline
and liquid TAG’s “Stearins”
 Lipid content, physical properties, and
preservation are all highly important areas for
food research, analysis, and product
development.
 Many preservation and packaging schemes are
aimed at prevention of lipid oxidation.
 Oil-
Nomenclature
 The
first letter C represents Carbon
 The number after C and before the colon
indicates the Number of Carbons
 The letter after the colon shows the Number of
Double Bonds
 ·The letter n (or w) and the last number indicate
the Position of the Double Bonds
Saturated Fatty Acids
Mono-Unsaturated Fatty Acids
Poly-Unsaturated Fatty Acids
Lipids
Properties depend on structure
 Length of fatty acids (# of carbons)

Short chains will be liquid, even if saturated (C4 to C10)
Position of fatty acids (1st, 2nd, 3rd)
 Degree of unsaturation:

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Double bonds tend to make them a liquid oil
Hydrogenation: tends to make a solid fat
Unsaturated fats oxidize faster
 Preventing lipid oxidation is a constant battle in the
food industry
Lipids 101-What are we talking about?
 Fatty
acid profile- quantitative determination of the
amount and type of fatty acids present following
hydrolysis.
 To help orient ourselves, we start counting the
number of carbons starting with “1” at the
carboxylic acid end.
O
C C C C C C C C C C C C C C C C C C
18
1
OH
Lipids 101-What are we talking about?
 For
the “18-series” (18:0, 18:1, 18:2, 18:3) the
double bonds are usually located between carbons
6=7 9=10 12=13 15=16.
O
C C C C C C C C C C C C C C C C C C
18
16 15 13 12 10 9
1
OH
Lipids 101-What are we talking about?
 The
biomedical field entered the picture and ruined
what food scientists have been doing for years with
the OMEGA (w) system (or “n” fatty acids).
 With this system, you count just the opposite.
 Begin counting with the methyl end
 Now the 15=16 double bond is a 3=4 double bond or
as the biomedical folks call it….an w-3 fatty acid
C
C C C C C C C C C C C C C C C C C C
1
6 7
3 4
18
9 10
OH
Melting Points of Lipids
Tuning Fork Analogy-TAG’s
Envision a Triacylglyceride as a loosely-jointed E
 Now, pick up the compound by the middle chain,
allowing the bottom chain to hang downward in a
straight line.
 The top chain will then curve forward and form an

h
Thus the “tuning fork” shape
 Fats will tilt and twist to this lowest free energy
level

Lipids

Lipids are categorized into two broad classes.

The first, simple lipids, upon hydrolysis, yield up to two types
of primary products, i.e., a glycerol molecule and fatty acid(s).

The other, complex lipids, yields three or more primary
hydrolysis products.

Most complex lipids are either glycerophospholipids, or
simply phospholipids


contain a polar phosphorus moiety and a glycerol backbone
or glycolipids, which contain a polar carbohydrate moiety
instead of phosphorus.
Lipids
Other types of lipids
Phospholipids
 Structure similar to triacylglycerol
 High in vegetable oil
 Egg yolks
 Act as emulsifiers
Fats and Oils…
can also be converted
to an emulsifier…
H
O
H
C
O C Fatty Acid Chain
H
C
OH
H
C
OH
Production of mono- and diglycerides H
 Use
as Emulsifiers
 Heat fat or oil to ~200°C
 Add glycerol and alkali
 Free Fatty Acids will be added to the glycerol
Fats and Oils: Processing
Extraction
 Rendering
 Pressing oilseeds
 Solvent extraction
Soybean
Peanut
Rape Seed
Safflower
Sesame
Fats and Oils
Further Processing

Degumming


Refining/Neutralization

Oil
Refining

Remove free fatty acids (alkali +
water)
Bleaching


Remove phospholipids with water
Remove pigments (charcoal filters)
Deodorization

Remove off-odors (steam, vacuum)
Where Do We Get Fats and Oils?
Neutralization
 Free fatty acids, phospholipids, pigments, and waxes exist in the crude oil
 These may promote lipid oxidation and off-flavors
 Removed by heating fats and adding caustic soda (sodium hydroxide) or soda
ash (sodium carbonate).
 Impurities settle to the bottom and are drawn off.
 The refined oils are lighter in color, less viscous, and more susceptible to
oxidation.
Bleaching
 The removal of color materials in the oil.
 Heated oil can be treated with diatomaceous earth, activated carbon, or
activated clays.
 Colored impurities include chlorophyll and carotenoids
 Bleaching can promote lipid oxidation since some natural antioxidants are
removed.
Where Do We Get Fats and Oils?
Deodorization
 Deodorization is the final step in the refining of oils.
 Steam distillation under reduced pressure (vacuum).
 Conducted at high temperatures of 235 - 250ºC.
 Volatile compounds with undesirable odors and tastes
can be removed.
 The resultant oil is referred to as "refined" and is ready
to be consumed.
 About 0.01% citric acid may be added to inactivate prooxidant metals.
Where Do We Get Fats and Oils?

Rendering
 Primarily for extracting oils from animal tissues.
 Oil-bearing tissues are chopped into small pieces and
boiled in water.
 The oil floats to the surface of the water and skimmed.
 Water, carbohydrates, proteins, and phospholipids
remain in the aqueous phase and are removed from the
oil.
 Degumming may be performed to remove excess
phospholipids.
 Remaining proteins are often used as animal feeds or
fertilizers.
Where Do We Get Fats and Oils?


Mechanical Pressing
Mechanical pressing is often used to extract oil from
seeds and nuts with oil >50%.
 Prior to pressing, seed kernels or meats are ground into
small sized to rupture cellular structures.
 The coarse meal is then heated (optional) and pressed in
hydraulic or screw presses to extract the oil.
 Olive oils is commonly cold pressed to get virgin or
extra virgin olive oil. It contains the least amount of
impurities and is often edible without further processing.
 Some oilseeds are first pressed or placed into a screwpress to remove a large proportion of the oil before
solvent extraction.
Where Do We Get Fats and Oils?

Solvent Extraction
 Organic solvents such as petroleum ether, hexane, and 2-propanol can be added
to ground or flaked oilseeds to recover oil.
 The solvent is separated from the meal, and evaporated from the oil.
Neutralization
 Free fatty acids, phospholipids, pigments, and waxes exist in the crude oil
 These promote lipid oxidation and off-flavors
 Removed by heating fats and adding caustic soda (sodium hydroxide) or soda
ash (sodium carbonate).
 Impurities settle to the bottom and are drawn off.
 The refined oils are lighter in color, less viscous, and more susceptible to
oxidation.
Bleaching
 The removal of color materials in the oil.
 Heated oil can be treated with diatomaceous earth, activated carbon, or
activated clays.
 Colored impurities include chlorophyll and carotenoids
 Bleaching can promote lipid oxidation since some natural antioxidants are
removed.
Hydrogenating Vegetable oils can
produce trans-fats
H H
C C
Cis-
H
C C
Trans-
H
http://www.foodnavigator-usa.com/Regulation/Trans-fats-Partially-hydrogenated-oils-should-be-phasedout-in-months-not-years-says-expert-as-FDA-considers-revoking-their-GRAS-status
The cis- and trans- forms of a fatty acid
Lipid Oxidation
Effects of Lipid Oxidation

Flavor and Quality Loss





Nutritional Quality Loss



Rancid flavor
Alteration of color and texture
Decreased consumer acceptance
Financial loss
Oxidation of essential fatty acids
Loss of fat-soluble vitamins
Health Risks


Development of potentially toxic compounds
Development of coronary heart disease
Simplified scheme of lipoxidation
H H H H
H H H H
H H H H
R C C C C R
R C C C C R
R C C C C R
H
H
+ Catalyst
H
*
+ Oxygen
H
O
O
LIPID OXIDATION and Antioxidants




Fats are susceptible to hydrolyis (heat, acid, or lipase enzymes)
as well as oxidation. In each case, the end result can be
RANCIDITY.
For oxidative rancidity to occur, molecular oxygen from the
environment must interact with UNSATURATED fatty acids in
a food.
The product is called a peroxide radical, which can combine with
H to produce a hydroperoxide radical.
The chemical process of oxidative rancidity involves a series of
steps, typically referred to as:



Initiation
Propagation
Termination
Lipid Oxidation
Initiation of Lipid Oxidation

There must be a catalytic event that causes the initiation of
the oxidative process


Enzyme catalyzed
“Auto-oxidation”
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Excited oxygen states (i.e singlet oxygen): 1O2
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Triplet oxygen (ground state) has 2 unpaired electrons in the same spin in
different orbitals.
Singlet oxygen (excited state) has 2 unpaired electrons of opposite spin in the
same orbital.
Metal ion induced (iron, copper, etc)
Light
Heat
Free radicals
Pro-oxidants
Chlorophyll
Water activity
Considerations for Lipid Oxidation
 Which
hydrogen will be lost from an unsaturated
fatty acid?
 The longer the chain and the more double
bonds….the lower the energy needed.
Oleic acid
Radical Damage,
Hydrogen
Abstraction
Formation of a
Peroxyl Radical
Propagation Reactions
Initiation
Ground state oxygen
Hydroperoxide
decomposition
Peroxyl radical
Start all over again…
Hydroperoxide
New
Radical
Hydroxyl radical!!
Propagation of Lipid Oxidation
H H H H
H H H H
H H H H
R C C C C R
R C C C C R
R C C C C R
H
H
+ Catalyst
H
*
+ Oxygen
H
O
O
Termination of Lipid Oxidation
Although radicals can “meet” and terminate propagation
by sharing electrons….
 The presence or addition of antioxidants is the best way in
a food system.
 Antioxidants can donate an electron without becoming a
free radical itself.
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Antioxidants and Lipid Oxidation
BHT – butylated hydroxytoluene
 BHA – butylated hydroxyanisole
 TBHQ – tertiary butylhydroquinone
 Propyl gallate
 Tocopherol – vitamin E
 NDGA – nordihydroguaiaretic acid
 Carotenoids
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Physical Properties of Lipids
Fats and Oils
Melting and Texture
Think of a fat as a crystal, that when heated will
melt.
 Length of fatty acid chain
 Short
chains have low melting points
 Oils
vs soft fats vs hard fats
 Degree of unsaturation
 Unsaturation
= presence of double bonds
 Unsaturation = low melting point
Fats and Oils in Foods
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SOLID FATS are made up of microscopic fat crystals. Many fats
are considered semi-solid, or “plastic”.
PLASTICITY is a term to describe a fat’s softness or the
temperature range over which it remains a solid.
Even a fat that appears liquid at room temperature contains a small number of
microscopic solid fat crystals suspended in the oil…..and vice versa
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PLASTIC FATS are a 2 phase system:
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Plasticity is a result of the ratio of solid to liquid components.
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Solid phase (the fat crystals)
Liquid phase (the oil surrounding the crystals).
Plasticity ratio = volume of crystals / volume of oil
Measured by a ‘solid fat index’ or amount of solid fat or liquid oil in a lipid
As the temperature of a plastic fat increases the fat crystals melt
and the fat will soften and eventually turn to a liquid.
Shortening
Plastic range
 Temperature range over which it is solid
(melting point)
 Want a large plastic range for shortening
 Want it to remain a solid at high temps.
 Holding
air during baking
Frying Oils
Want a short plastic range
 Liquid or low melting point
 Do not want mono- or diglycerides or oil
will smoke when heated
 Must be stable to oxidation, darkening
 Methyl silicone may be added to help
reduce foaming
Fat and Oil: Further Processing
 Winterizing
 Cooling
a lipid to precipitate solid fat crystals
 DIFFERENT from hydrogenation
 Plasticizing
 Modifying
fats by melting (heating) and solidifying
(cooling)
 Tempering
 Holding
the fat at a low temperature for several
hours to several days to alter fat crystal properties
(Fat will hold more air, emulsify better, and have
a more consistent melting point)
Fat Crystals: α, ß’, ß
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The proportion of fat crystals to oil also depends on the melting points
of the crystals.
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Most fats exhibit polymorphism, meaning they can exist in one of
several crystal forms. These crystal forms are 3-D arrangements.
Three primary crystal forms exist:
 α-form (not very dense, lowest melting point), unstable
 ß’-form (moderate density, moderate melting point), not as stable
 ß-form (most dense, highest melting point), very stable
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Rapid cooling of a heated fat will result in fine α crystals.
Slow cooling favors formation of the coarse ß crystals.
Fat crystals are easily observed when butter/shortening is melted and
allowed to re-solidify.
Fat Crystals in Commercial Oils
α, ß’, ß
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Crystal forms are largely dependent on the fatty acid
composition of the lipid
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Some fats will only solidify to the ß-form
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Soybean, peanut, corn, olive, coconut, cocoa butter, etc
Other fats will harden to the ß’-form
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Mono-acid lipids (3 of the same fatty acids)
Mixed lipids or heterogeneous lipids (different FA’s)
Cottonseed, palm, canola, milk fat, and beef tallow
ß’ forms are good for baked goods, where a high plastic
range is desired…..but...
Chocolate Bloom
 In
chocolate (cocoa butter), the desired stable
crystal form is the ß-form
 Processing involves conching (blending cocoa
and sugar to a super-fine particle) and
 Tempering (heating/cooling steps).
 Together, these give ß crystals to the final
chocolate
 Fine chocolates control this well.
Chocolate
Making chocolate
 The polymorphs of chocolate affect quality and keeping quality.
 When making chocolate, the tempering process alters the fat crystals and
transforms to a predominance of ß-forms.
 This process begins with the formation of some ß crystals as “seeds” from
which additional crystals form.
 The chocolate is then heated to just below the temperature for ß-forms to melt
(thus melting all other forms), and allows the remaining fats to crystalize into
ß-forms upon cooling.
Chocolate Bloom
 When chocolate has been heated and cooled, fat and sugar can rise to the
surface, and change crystalline state (fat) or crystallize (sugar).
 When melted fat re-cools, less stable and lower melting point α crystals can
form.
 The different crystals also physically look different (white, grey, etc) against
the brown background of the chocolate bar.