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Proteins

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Title: Proteins


1
Proteins
  • From the Greek proteios or primary.

2
Properties of Amino Acids
  • Zwitterions are electrically neutral, but carry a
    formal positive or negative charge.
  • Give proteins their water solubility

3
Shape Interactions of Proteins
4
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

5
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

6
Functional Properties of Proteins
  • 3 major categories
  • Hydration properties
  • Protein to water interactions
  • Dispersion, solubility, adhesion, viscosity
  • Water holding capacity
  • Structure formation
  • Protein to protein interactions
  • Gel formation, precipitation, aggregation
  • Surface properties
  • Protein to interface interactions
  • Foaming and emulsification

7
1. Hydration Properties (protein to water)
  • Most foods are hydrated to some extent.
  • 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
  • Influenced by pH
  • Swelling of proteins
  • Overall solubility of a protein

8
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)

9
3. Surface Properties (protein to interface)
  • Emulsions- Ability for a protein to unfold
    (tertiary denaturation) and expose hydrophobic
    sites that can interact with lipids.
  • 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
  • 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

10
Factors Affecting Changes to Proteins
  • Denaturation
  • Aggregation
  • Salts
  • Gelation

11
Changes to Proteins
  • Native State
  • 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
  • Acids
  • Alkali
  • Salts
  • Heat
  • Alcohol
  • Pressure
  • Mixing (shear)
  • Oxidants (form bonds) and antioxidants (break
    bonds)

12
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

13
Changes to Proteins
  • Temperature is the most common way to denature a
    protein
  • Both hot and cold conditions affect proteins
  • Every tried to freeze milk? Eggs?
  • Heating affects the tertiary structure
  • Mild heat can activate enzymes
  • Hydrogen and ionic bonds dissociate
  • Hydrophobic regions are exposed
  • Hydration increases, or entraps water
  • Viscosity increases accordingly

14
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.

15
Isoelectric Precipitations
  • Proteins have no net charge at their IEP

- -
- -
- -
- -
Strong Repulsion (net negative charge)
- -
- -
- -
- -
- -
- -
- -
- -
- -
- -


Aggregation (net neutral charge)


- -
- -
- -
- -






Strong Repulsion (net positive charge)








16
Isoelectric Precipitations
  • Proteins can be salted out, adding charges

- -
- -


- -

Aggregation (net neutral charge)
- -

- -
- -


Na
Na
Cl-
Na
Cl-
Cl-
17
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 measure quantitatively
  • The pellet will be insoluble protein
  • The supernatant will be soluble protein

18
Gel Formation
  • Many foods owe their physical properties to a gel
    formation. Influences quality and perception.
  • Cheese, fermented dairy, hotdogs, custards, etc
  • As little as 1 protein may be needed to form a
    rigid gel for a food.
  • Most protein-based gels are thermally-induced
  • Cause water to be entrapped, and a gel-matrix
    formation
  • Thermally irreversible gels are most common
  • Gel formed during heating, maintained after
    cooling
  • Will not reform when re-heated and cooled
  • Thermally reversible gels
  • Gel formed after heating/cooling. Added heat will
    melt the gel.

19
What is more important in foods?Protein
precipitationorProtein solubilization???
20
Effects of Food Processing
21
Processing and Storage
  • Decreases spoilage of foods, increases shelf life
  • Loss of nutritional value in some cases
  • Severity of processing
  • Loss of functionality
  • Denatured proteins have far fewer functional
    aspects
  • Both desirable and undesirable flavor changes

22
Processing and Storage
  • Proteins are affected by
  • Heat
  • Extremes in pH (remember the freezing example?)
  • Oxidizing conditions
  • Oxidizing additives, lipid oxidation,
    pro-oxidants
  • Reactions with reducing sugars in browning rxns

23
Processing and Storage
  • Mild heat treatments (lt 100C)
  • May slightly reduce protein solubility
  • Cause some denaturation
  • Can inactive some enzymes
  • Improves digestibility of some proteins
  • Severe heat treatments (for example gt100C)
  • Some sulfur amino acids are damaged
  • Release of hydrogen sulfide, etc (stinky)
  • Deamination can occur
  • Release of ammonia (stinky)
  • Very high temperatures (gt180C)
  • Some of the roasted smells that occur with
    peanuts or coffee

24
Enzymes
  • A quick review, since we
  • know the basics already

25
Enzyme Influencing Factors
  • Enzymes are proteins that act as biological
    catalysts
  • They are influenced in foods by
  • Temperature
  • pH
  • Water activity
  • Ionic strength (ie. Salt concentrations)
  • Presence of other agents in solution
  • Metal chelators
  • Reducing agents
  • Other inhibitors

Also factors for Inhibition, including Oxygen
exclusion and Sulfites
26
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 30-40C
  • Many enzymes denature gt45C
  • Each enzyme is different, and vary by isozymes
  • Often an enzyme is at is maximal activity just
    before it denatures at its maximum temperature

27
pH
  • Like temp, enzymes have an optimal pH where they
    are maximally active
  • Generally between pH 4 and 8
  • with many exceptions
  • Most have a very narrow pH range where they show
    activity.
  • This influences their selectivity and activity.

28
  • 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

29
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

30
Enzymes
  • The effect of temperature is two-fold
  • From about 20, to 35-40C (for enzymes)
  • From about 5-35C for other reactions
  • Q10-Principal For every 10C 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

31
Enzymes
  • Enzymes are sensitive to pH most enzymes active
    only within a pH range of 3-4 units (catalase has
    max. activity between pH 3 10!)
  • The optimum pH depends on the nature of the
    enzyme and reflects the environmental conditions
    in which enzyme is normally active
  • 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.

32
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
  • 3- hydrolases (class)
  • 2- glucosidase (sub-class)
  • 1- hydrolyzing O-glycosidic bond (sub-sub-class)
  • 1- specific enzyme

33
Enzyme Class Characterizations
  • Oxidoreductase
  • Oxidation/reduction reactions
  • Transferase
  • Transfer of one molecule to another (i.e.
    functional groups)
  • Hydrolase
  • Catalyze bond breaking using water (ie.
    protease, lipase)
  • Lyase
  • Catalyze the formation of double bonds, often in
    dehydration reations
  • Isomerase
  • Catalyze intramolecular rearrangement of
    molecules
  • Ligase
  • Catalyze covalent attachment of two substrate
    molecules

34
1. OXIDOREDUCTASES
Oxidation Is Losing electrons
Reduction Is Gaining electrons
Electron acceptor
e-
Xm Xm2
reduced
e-
oxidized
Electron donor
35
1. Oxidoreductases GLUCOSE OXIDASE
  • ?-D-glucose oxygen oxidoreductase
  • Catalyzes oxidation of glucose to glucono- ?
    -lactone
  • ?-D-glucose Glucose oxidase D glucono-?-lactone

FAD FADH2 H2O
H2O2 O2 D Gluconic acid
Catalase
H2O ½ O2
Oxidation of glucose to gluconic acid
36
1. Oxidoreductases Catalase
  • hydrogenperoxide hydrogenperoxide oxidoreductase
  • Catalyzes conversion of 2 molecules of H2O2 into
    water and 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

H2O2 -------------------? H2O 1/2 O2
37
1. Oxidoreductases PEROXIDASE (POD)
  • donor hydrogenperoxide oxidoreductase
  • Iron-containing enzyme. Has a heme
  • prosthetic group
  • Thermo-resistant denaturation at 85oC
  • Since is thermoresistant - indicator of proper
    blanching (no POD activity in blanched
    vegetables)

38
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
PPO o-Quinone H2O Gallocatechins O2 Catechi
n gallates Colored products Action of PPO
during tea fermentation apple/banana browning
39
1. Oxidoreductases LIPOXYGENASE
H
H
..
H

C
C
C
cis
C
cis
C
H
H
O2
H
H
H
H
C
C
..
C
C
C
cis
trans
OOH
H
Oxidation of lipids with cis, cis groups to
conjugated cis, trans hydroperoxides.
40
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.

41
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.

42
Worthington Enzyme Manual
  • http//www.worthington-biochem.com/index/manual.ht
    ml

IUPAC-IUBMB-JCBN http//www.chem.qmul.ac.uk/iubmb/
enzyme
43
Lipids
44
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 food texture
  • Solids or liquids at room temperature
  • Change with changing temperature
  • Participation in emulsions

45
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

46
Lipids
  • Neutral Lipids
  • Triacylglycerols
  • Waxes
  • Long-chain alcohols (20 carbons in length)
  • Cholesterol esters
  • Vitamin A esters
  • Vitamin D esters
  • Conjugated Lipids
  • Phospholipids, glycolipids, sulfolipids
  • Derived Lipids
  • Fatty acids, fatty alcohols/aldehydes,
    hydrocarbons
  • Fat-soluble vitamins

47
Lipids
  • Structure
  • Triglycerides or triacylglycerols
  • Glycerol 3 fatty acids
  • gt20 different fatty acids

48
Lipids 101-What are we talking about?
  • Fatty acids- the building block of fats
  • A fat with no double bonds in its 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 (160, 161, 182 etc)

49
Lipids
  • Oil- liquid triacylglycerides Oleins
  • Fat- solid or semi-solid mixtures of crystalline
    and liquid TAGs 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.

50
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

51
Saturated Fatty Acids
52
Mono-Unsaturated Fatty Acids
53
Poly-Unsaturated Fatty Acids
54
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
  • 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

55
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.

56
Lipids 101-What are we talking about?
  • For the 18-series (180, 181, 182, 183) the
    double bonds are usually located between carbons
    67 910 1213 1516.

57
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 1516 double bond is a 34 double bond or
    as the biomedical folks call it.an w-3 fatty acid

58
Melting Points of Lipids
59
Tuning Fork Analogy-TAGs
  • 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

60
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 glycerophospholipid
    s, or simply phospholipids
  • contain a polar phosphorus moiety and a glycerol
    backbone
  • or glycolipids, which contain a polar
    carbohydrate moiety instead of phosphorus.

61
Lipids
62
Other types of lipids
  • Phospholipids
  • Structure similar to triacylglycerol
  • High in vegetable oil
  • Egg yolks
  • Act as emulsifiers

63
Fats and Oilscan also be convertedto an
emulsifier
  • Production of mono- and diglycerides
  • Use as Emulsifiers
  • Heat fat or oil to 200C
  • Add glycerol and alkali
  • Free Fatty Acids will be added to the glycerol

64
Fats and Oils Processing
Peanut
  • Extraction
  • Rendering
  • Pressing oilseeds
  • Solvent extraction

Rape Seed
Safflower
Sesame
Soybean
65
Fats and OilsFurther Processing
  • Degumming
  • Remove phospholipids with water
  • Refining/Neutralization
  • Remove free fatty acids (alkali water)
  • Bleaching
  • Remove pigments (charcoal filters)
  • Deodorization
  • Remove off-odors (steam, vacuum)

Oil Refining
66
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.

67
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 pro-oxidant metals.

68
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.

69
Where Do We Get Fats and Oils?
  • Mechanical Pressing
  • Mechanical pressing is often used to extract oil
    from seeds and nuts with oil gt50. 
  • 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
    screw-press to remove a large proportion of the
    oil before solvent extraction.

70
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.

71
Hydrogenating Vegetable oils can produce
trans-fats
Cis-
Trans-
http//www.foodnavigator-usa.com/Regulation/Trans-
fats-Partially-hydrogenated-oils-should-be-phased-
out-in-months-not-years-says-expert-as-FDA-conside
rs-revoking-their-GRAS-status
72
The cis- and trans- forms of a fatty acid
73
(No Transcript)
74
Lipid Oxidation
75
Effects of Lipid Oxidation
  • Flavor and Quality Loss
  • Rancid flavor
  • Alteration of color and texture
  • Decreased consumer acceptance
  • Financial loss
  • Nutritional Quality Loss
  • Oxidation of essential fatty acids
  • Loss of fat-soluble vitamins
  • Health Risks
  • Development of potentially toxic compounds
  • Development of coronary heart disease

76
Simplified scheme of lipoxidation
Oxygen
Catalyst
77
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

78
Lipid Oxidation
79
Initiation of Lipid Oxidation
  • There must be a catalytic event that causes the
    initiation of the oxidative process
  • Enzyme catalyzed
  • Auto-oxidation
  • Excited oxygen states (i.e singlet oxygen) 1O2
  • 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

80
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.

81
Oleic acid
Radical Damage, Hydrogen Abstraction
Formation of a Peroxyl Radical
82
Propagation Reactions
Peroxyl radical
Ground state oxygen
Initiation
Hydroperoxide
New Radical
Hydroxyl radical!!
Hydroperoxide decomposition
Start all over again
83
Propagation of Lipid Oxidation
Oxygen
Catalyst
84
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.

85
Antioxidants and Lipid Oxidation
  • BHT butylated hydroxytoluene
  • BHA butylated hydroxyanisole
  • TBHQ tertiary butylhydroquinone
  • Propyl gallate
  • Tocopherol vitamin E
  • NDGA nordihydroguaiaretic acid
  • Carotenoids

86
Physical Properties of Lipids
87
Fats and OilsMelting 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

88
Fats and Oils in Foods
  • SOLID FATS are made up of microscopic fat
    crystals. Many fats are considered semi-solid, or
    plastic.
  • PLASTICITY is a term to describe a fats 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
  • PLASTIC FATS are a 2 phase system
  • Solid phase (the fat crystals)
  • Liquid phase (the oil surrounding the crystals).
  • Plasticity is a result of the ratio of solid to
    liquid components.
  • 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.

89
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

90
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

91
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)

92
Fat Crystals a, ß, ß
  • The proportion of fat crystals to oil also
    depends on the melting points of the crystals.
  • 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
  • a-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
  • Rapid cooling of a heated fat will result in fine
    a 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.

93
Fat Crystals in Commercial Oilsa, ß, ß
  • Crystal forms are largely dependent on the fatty
    acid composition of the lipid
  • Mono-acid lipids (3 of the same fatty acids)
  • Mixed lipids or heterogeneous lipids (different
    FAs)
  • Some fats will only solidify to the ß-form
  • Soybean, peanut, corn, olive, coconut, cocoa
    butter, etc
  • Other fats will harden to the ß-form
  • Cottonseed, palm, canola, milk fat, and beef
    tallow
  • ß forms are good for baked goods, where a high
    plastic range is desired..but...

94
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.

95
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 a crystals can form.
  • The different crystals also physically look
    different (white, grey, etc) against the brown
    background of the chocolate bar.
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