Transcript Gelatinization of Starch

Angela Chen
Sweeteners
from
Starch….
Sweeteners from Starch….
Sweeteners from Starch….
Sweeteners from Starch….
Sweeteners from Starch….
Sweeteners from Starch….
Hydrocolloids
Binding water with carbohydrates
Starches- Our #1 Hydrocolloid?
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Hydrocolloids are substances that will form a gel or
add viscosity on addition of water.
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Most are polysaccharides and all form significant Hbonding with water with processing.
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Size, structure, and charge are the most important
factors relating to texture and physical features of
foods
Small versus Large
 Small
molecule sugars would create a high
osmotic pressure if stored in sufficient
quantities to be useful.
 Polymerized sugars reduce the number of
molecules present and hence the osmotic
effects.
 Free polymers are too thick to allow cell to
function
 Thus, plants store energy into starch granules
AMYLOSE
 Linear
polymer of glucose
 α 1 - 4 linkages
 Digestable by humans (4 kcal/g)
 250-350 glucose units on average
 Varies
 Corn,
widely
wheat, and potato starch
 ~10-30%
amylose
AMYLOPECTIN
 Branched
chain polymer of glucose
 α 1 - 4 and α 1 - 6 glycosidic linkages
 Mostly digestible by humans
 1,000 glucose units is common
 Branch
points every ~15-25 units
Starch
 Amylose
may have a few branched chains
 Helical
structure with a hydrophobic core
 Core may contain lipids, metals, etc.
 Amylose
 Varies
 Waxy
to Amylopectin ratios ~ 1:4
with the plant source
starches are ~100% amylopectin
 Sugary “mutant” starches have more amylose
Straight-Chained Starch = Amylose
Glucose polymer linked α-1,4 and α-1,6
Starch

Birefringence When starch granules are
viewed under the microscope by polarized
light they exhibit a phenomenon known as
birefringency - the refraction of polarized
light by the intact crystalline regions to give a
characteristic "Maltese cross" pattern on each
granule. The cross disappears upon heating
and gelatinization.
Modified Starches
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Gelatinization is the easiest modification
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Heated in water then dried.
Acid and/heat will form “dextrins”
 α-Amylase
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β-Amylase
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hydrolyzes α (1-4) linkage
random attack to make shorter chains
Also attacks α (1 - 4) linkages
Starts at the non-reducing end of the starch chain
Gives short dextrins and maltose
Both enzymes have trouble with α (1 - 6) linkages
Gelatinization of Starch
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Native starch granules are insoluble in cold water, despite
some “swelling”
 Heated water increases kinetic energy, breaking some
intermolecular bonds, and allows water to penetrate
 The gelatinization point is where crystallinity is lost
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GTR is the temperature range over which gelatinization
occurs.
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As water is bound, the viscosity increases.
GTR is different from different starch types
There must be enough water to break open and bind to
the starch hydrogen binding sites.
Gelatinization
Starch grains swell when heated in water
H-bonds break, amylose can spill from the grain
Gains may loose integrity
Gelatinization is done
During cooling, junction zones form
Between amylose and amylopectin
water
water
water
water
water
water
Water is trapped
Forming a gel.
WATER
As the gel dehydrates and/or junction zones
Tighten, water is “squeezed” from the gel, in
a syneresis process.
Starch Modifications
 Cross-linking (common modification)
 Alkali
treatment (pH 7.5-12) with salt
Phosphorus oxychloride
 Sodium trimetaphosphate
 Adipic and acetic anhydride
 Starch phosphates formed after neutralization
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Cross-Linking
 Resists
viscosity breakdown
 Resists prolonged heating effects
 Resists high shear rates
 Resists high acid environments
 Increased viscosity
 Increased texture
Starch Modifications
 Starch
Substitutions
 Adding
monofunctional groups
“Blocking Groups” added to the starch
 Acetyl (2.5% max starch acetates)
 Hydroxypropyl, phosphates, ethers
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 Slows
retrogradation (re-association of amylose)
 Lowers GTR, stabilizes the starch
Acetate + Starch
Starch Modifications
 Oxidation and
Bleaching
Hydrogen peroxide
 Ammonium persulfate
 Na/Ca hypochlorite
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
0.0082 lbs chlorine/pound of starch
K-permanganate
 Na-chlorite

 Whitens

the starch
Removes carotenes and other natural pigments
 ~25%
of oxidizers break C-C linages
 ~75% of oxidizers will oxidize the hydroxyl groups
 Lowers viscosity, improves clarity of gels
Polysaccharide Breakdown Products
Hydrolytic Products
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Maltose
Maltitol
Maltodextrins
Dextrins
Dextrans
Maltose = glucose disaccharide
Maltitol = example of a “polyol”
Maltodextrins = enzyme converted starch fragments
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Dextrins = starch fragments (α-1-4) linkages produced by
hydrolysis of amylose
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Dextrans = polysaccharides made by bacteria and yeast
metabolism, fragments with mostly α (1 - 6) linkages
Maltodextrins and enzyme-converted starch:
STARCH
fermentation
SUGARS
ETHANOL
MODIFIED STARCHES
GELATINIZED STARCH
alpha amylase
Maltodextrins
Corn Syrups
Sugars
The smaller the size of the products in these reactions, the
higher the dextrose equivalence (DE), and the sweeter
they are
Starch DE = 0
Glucose (dextrose) DE = 100
Maltodextrin (MD) DE is <20
Corn syrup solids (CS) DE is >20
Low DE syrup
alpha amylase
MD
beta amylase
High
DE
Syrup
Dextrinization
A
non-enzymatic method to product lowmolecular weight fragments
 High
heat treatment of acidified starch
 “Pyro-conversion” of starch to dextrins
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Both breaks and re-forms bonds
 Wide-range
of products formed
Vary in viscosity
 Solubility
 Color (white, yellow)
 Reducing capacity
 Stability
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Hydrocolloids
Binding water with carbohydrates
“Gums”
“Vegetable gum” polysaccharides are substances derived
from plants, including seaweed and various shrubs or trees,
have the ability to hold water, and often act as thickeners,
stabilizers, or gelling agents in various food products.
Plant gums - exudates, seeds
(guar, xanthan, locust bean, etc)
Marine hydrocolloids - extracts from seaweeds
(Carageenan, agar, alginates)
Microbiological polysaccharides - exocellular polysaccharides
Modified, natural polysaccharides
FUNCTIONS IN FOOD

Gelation
 Viscosity
 Suspension
 Emulsification and stability
 Whipping
 Freeze thaw protection
 Fiber (dietary fiber)


Gut health
Binds cholesterol
STRUCTURAL CONSIDERATIONS
 Electrical
charge, pH sensitive
 Interactions
with
Oppositely charged molecules
 Salts
 Acids

 Chain
length
 Longer
 Linear
chains are more viscous
vs Branched chains
 Inter-entangled,
enter-woven molecules
“Structural” Polysaccharides
Cellulose
 Polymer of glucose linked ß-1,4
Hemicellulose
 Similar to cellulose
 Consist of glucose and other monosaccharides
 Arabinose,
xylose, other 5-carbon sugars
Pectin
 Polymer of galacturonic acid
MODIFIED CELLULOSES
 Chemically
modified cellulose
 Do not occur naturally in plants
 Similar to starch, but β-(1,4) glycosidic bonds
 Carboxymethyl cellulose (CMC) most common
 Acid
treatment to add a methyl group
 Increases water solubility, thickening agent
 Sensitive to salts and low pH
 Fruit
fillings, custards, processed cheeses, high
fiber filler
PECTINS
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Linear polymers of galacturonic acid
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Susceptible to degrading enzymes
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Gels form with degree of methylation of its carboxylic acid
groups
Many natural sources
Polygalacturonase (depolymerize)
Pectin esterases (remove methyl groups)
Longer polymers, higher viscosity
 Lower methylation, lower viscosity
 Increase electrolytes (ie. metal cations), higher viscosity
 pH and soluble solids impact viscosity
PECTIC SUBSTANCES: cell cementing compound; fruits and vegetables;
pectin will form gel with appropriate concentration, amount of sugar and pH.
Basic unit comprised of galacturonic acid.
BETA-GLUCANS
 Extracts
from the bran of barley and oats
 Long glucose chains with mixed ß-linkages
 Very large (~250,000 glucose units)
 Water
soluble, but have a low viscosity
 Can be used as a fat replacer
 Responsible for the health claims (cholesterol) for
whole oat products
 Formulated to reduce the glycemic index of a food
Beta-Glucan
Beta-glucans occur in the bran of grains such as barley
and oats, and they are recognized as being beneficial for
reducing heart disease by lowering cholesterol and reducing
the glycemic response.
They are used commercially to modify food texture. and as fat replacer .
Beta-Glucan
Others
CHITIN
 Polymer of N-Acetyl-D-glucosamine
 Found in the exoskeleton of insects and shellfish
 Many uses in industry, food and non-food.
INULIN
 Chains of fructose that end in a glucose molecule
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Generally a sweet taste
Isolated from Jerusalem artichokes and chicory
Act as a dietary fiber
Potentially a pre-biotic compound
Paper Review
Producing fructo-oligosaccharides: For Tuesday
Starch
 Starch
must be cooked to act as a thickening
agent
 Pre-gelatinized starch is made by quickly
cooking a starch and drying the product.
 Pre-gelatinized starch rapidly re-hydrates
without further cooking
 Useful
thickening agent
 Can be used in dried sauces and salad dressings
 Used in products that do not require more cooking
Starch
 Starch
suspensions are not stable to heating
 Swollen starch granules break down in hot,
stirred or acidic conditions
 Combinations (ie. heat and acid) will
depolymerize
 Cross-linking can help stabilize and slow or
maybe prevent breakdown
Starch

Starch gels change their properties during storage
 Slow retrogradation of amylopectin is common
 The texture of a starch gel will change and show some
syneresis.
 Again, modified starch will resist changes during
storage
 Starch acetates or phosphates are common
modifications, altering the helical arrangements, and
slow or inhibit retrogradation.
 All stabilized starches must also be labeled as
“modified starch” on an ingredient list.
“Vegetable gum” polysaccharides are substances derived
from plants, including seaweed and various shrubs or trees,
have the ability to hold water, and often act as thickeners,
stabilizers, or gelling agents in various food products.
Plant gums - exudates, seeds
(guar, xanthan, locust bean, etc)
Marine hydrocolloids - extracts from seaweeds
(Carageenan, agar, alginates)
Microbiological polysaccharides - exocellular polysaccharides
Modified, natural polysaccharides
FUNCTIONS IN FOOD

Gelation
 Viscosity
 Suspension
 Emulsification and stability
 Whipping
 Freeze thaw protection
 Fiber (dietary fiber)


Gut health
Binds cholesterol
STRUCTURAL CONSIDERATIONS
 Electrical
charge, pH sensitive
 Interactions
with
Oppositely charged molecules
 Salts
 Acids

 Chain
length
 Longer
 Linear
chains are more viscous
vs Branched chains
 Inter-entangled,
enter-woven molecules
“Structural” Polysaccharides
Cellulose
 Polymer of glucose linked ß-1,4
Hemicellulose
 Similar to cellulose
 Consist of glucose and other monosaccharides
 Arabinose,
xylose, other 5-carbon sugars
Pectin
 Polymer of galacturonic acid
MODIFIED CELLULOSES
 Chemically
modified cellulose
 Do not occur naturally in plants
 Similar to starch, but β-(1,4) glycosidic bonds
 Carboxymethyl cellulose (CMC) most common
 Acid
treatment to add a methyl group
 Increases water solubility, thickening agent
 Sensitive to salts and low pH
 Fruit
fillings, custards, processed cheeses, high
fiber filler
PECTINS

Linear polymers of galacturonic acid



Susceptible to degrading enzymes



Gels form with degree of methylation of its carboxylic acid
groups
Many natural sources
Polygalacturonase (depolymerize)
Pectin esterases (remove methyl groups)
Longer polymers, higher viscosity
 Lower methylation, lower viscosity
 Increase electrolytes (ie. metal cations), higher viscosity
 pH and soluble solids impact viscosity
PECTIC SUBSTANCES: cell cementing compound; fruits and vegetables;
pectin will form gel with appropriate concentration, amount of sugar and pH.
Basic unit comprised of galacturonic acid.
BETA-GLUCANS
 Extracts
from the bran of barley and oats
 Long glucose chains with mixed ß-linkages
 Very large (~250,000 glucose units)
 Water
soluble, but have a low viscosity
 Can be used as a fat replacer
 Responsible for the health claims (cholesterol) for
whole oat products
 Formulated to reduce the glycemic index of a food
Beta-Glucan
Beta-glucans occur in the bran of grains such as barley
and oats, and they are recognized as being beneficial for
reducing heart disease by lowering cholesterol and reducing
the glycemic response.
They are used commercially to modify food texture. and as fat replacer .
Beta-Glucan
Yeast ß-Glucan Isolation
Sugar Reactions
(Gluconic acid)
(Glucuronic acid)
Properties of Glucose
 C1
of glucose is the carbonyl carbon
 Glucose has 4 chiral centers
 Non-super-imposable
 Carbons
on its mirror image
2, 3, 4, 5 are chiral carbons
 The
carbonyl carbon (C1) is also the site
of many reactions involving glucose
 They
have two enantiomeric forms, D and
L, depending on the location of the
hydroxyl group at the chiral carbons.
Sugars
 They
have two enantiomeric forms, D and L,
depending on the location of the hydroxyl group at
the chiral carbons.
 An
enantiomer is one of two stereoisomers that are
mirror images of each other, non-superposable.
 Isomerism
in which two isomers are mirror images
of each other. (D vs L).
 Vary in their 3-D space
Anomers
 An
anomer is one of a special pair of
diastereomeric (isomer) aldoses or ketoses
A
stereoisomer that is not an enantiomer
 They
differ only in configuration about the
carbonyl carbon (C1 for aldoses and C2 for
ketoses)
Carbonyl Carbons
 Carbonyl carbons
are subject to nucleophilic
attack, since it is electron deficient.
 Electrons

are drawn to this site
-OH groups on the sugar act as the nucleophile,
and add to the carbonyl carbon to recreate the
ring form
Carbonyl Carbons
 Anomers
 α-anomer
(~36%)
 β- anomer (~64%)
Sugar Anomers => Mutarotation
Interconversion of α- and β- anomers
The α- and β- anomers of carbohydrates are typically
stable.
 In solution, a single molecule can interchange between
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The process is
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straight and ring form
different ring sizes
α and β anomeric isomers
dynamic equilibrium
due to reversibility of reaction
All isomers can potentially exist in solution
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energy/stability of different forms vary
Mutarotation
 α-
and β- anomers
Isomerization
 Keto-Enol Tautomerism (equilibration)
 Hydrogen
 Enol
migration; switch from SB to DB
is predominant in aldose sugar
 Keto is predominant in ketose sugar
 Keto and Enol forms are tautomers of each other
Isomerization
 Glucose
and mannose are enantiomers, but
with dramatically different properties
 Glucose and fructose are isomers
Pectins in Foods
Plant Cell Wall
Middle
lamella
Nucleolus
Primary wall
Nucleus
Plasmalemma
Cytoplasm
Water-Filled
Vacuole
PECTINS
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Linear polymers of galacturonic acid
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Susceptible to degrading enzymes

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
Gels form with degree of methylation of its carboxylic acid
groups
Many natural sources
Polygalacturonase (depolymerize); PG
Pectin esterases (remove methyl groups), PME
Longer polymers, higher viscosity
 Lower methylation, lower viscosity
 Increase electrolytes (ie. metal cations), higher viscosity
 pH and soluble solids impact viscosity
Composition: polymer of galacturonic acids; may be partially esterified.
Pectic Acid
Pectin Molecule
Pectins

Pectins are important because they form gels
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Mechanism of gel formation differs by the degree of esterification
(DE) of the pectin molecules
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DE refers to that percentage of pectin units with a methyl group attached
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Free COOH groups can crosslink with divalent cations
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Sugar and acid under certain conditions can contribute to gel
structure and formation
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LM pectin “low methoxyl pectin” has DE < 50% ; gelatin is
controlled by adding cations (like Ca++ and controlling the pH)
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HM pectin “high methoxyl pectin” has DE >50% and forms a gel
under acidic conditions by hydrophobic interactions and Hbonding with dissolved solids (i.e. sugar)
Hydrophobic attractions between neighboring pectin polymer chains
promote gelation
Ca++
Ca++
Proteins
 Many
important functions
 Functional
 Nutritional
 Biological
 Enzymes
 Structurally complex and
large compounds
 Major source of nitrogen in the diet
 By
weight, proteins are about 16% nitrogen
Properties of Amino Acids
 Aliphatic
chains: Gly, Ala, Val, Leucine, Ile
 Hydroxy or sulfur side chains: Ser, Thr, Cys, Met
 Aromatic: Phe, Trp, Try
 Basic: His, Lys, Arg
 Acidic and their amides: Asp, Asn, Glu, Gln
Properties of Amino Acids:
Aliphatic Side Chains
Sulfur
Side
Chains
Aromatic Side Chains
Acidic Side Chains
Properties of Amino Acids:
 Zwitterions
are electrically neutral, but carry a
“formal” positive or negative charge.
The Zwitterion Nature
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Zwitterions make amino acids good acid-base buffers.
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Accepting H+ is acidic environments; donating H+ in basic environments
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For proteins and amino acids, the pH at which they have no net charge in
solution is called the Isoelectric Point of pI (i.e. IEP).

The solubility of a protein depends on the pH of the solution.

Similar to amino acids, proteins can be either positively or negatively charged
due to the terminal amine -NH2 and carboxyl (-COOH) groups.
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Proteins are positively charged at low pH and negatively charged at high pH.
When the net charge is zero, we are at the IEP.
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A charged protein helps interactions with water and increases its solubility.
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As a result, protein is the least soluble when the pH of the solution is at its
isoelectric point.
Physical Nature of Proteins
Secondary protein structure
 The
spatial structure the protein assumes along
its axis (its “native conformation” or min. free energy)
This gives a protein functional properties such as flexibility and strength
Tertiary Structure of Proteins
 3-D
organization of a polypeptide chain
 Compacts proteins
 Interior is mostly devoid of water or charge groups
3-D folding of chain
Quaternary Structure of Proteins
 Non-covalent associations
of protein units
Proteins
Changes in structure
 Denaturation
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Breaking of any structure except primary
Examples:
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Heat
Salt/Ions
Alcohol
pH extremes
Shear
Enzymes
Emulsoids and Suspensiods
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Proteins should be thought of as solids

Not in 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
Functional Properties of Proteins
3 major categories
 Hydration properties
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Structure formation
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Protein to water interactions
Dispersibility, solubility, adhesion,
Water holding capacity, viscosity
Protein to protein interactions
Gel formation, precipitation,
Aggregation
Surface properties
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Protein to interface interactions
Foaming, emulsification
1. Hydration Properties (hydration)

Proteins are important hydrocolloids
 As ingredients, many are sold as dry powders
 Hydrating and processing w/o denaturation

Solubility- Mostly, denatured proteins are less soluble than
native proteins
 Many (but not all) proteins (particularly suspensoids)
aggregate or precipitate at their isoelectric point (IEP)
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Protein viscosity is influenced by amount, size, shape, pH,
water content, and solubility of the proteins
2. Structure Formation (protein interactions)

Gels – a 3-D network of protein and water.

Attractive and repulsive forces between adjacent polypeptides
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Gelation- when denatured proteins aggregate and form an ordered
protein matrix
 Water absorption and thickening
 Formation of viscous, solid, or visco-elastic gels

For many proteins, heated followed by cooling forms the gel

Texturization – Proteins are responsible for the structure and
texture of many foods
 Meat, bread dough, gelatin
 Texturized proteins are modified with with salts, acid/alkali,
oxidants/reductants
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“Pink Slime”
Can also be processed to mimic other proteins (i.e. surimi)
3. Surface Properties (interfaces)
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Emulsions- Exposure of protein hydrophobic regions to
lipids (ie. tertiary structures)
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Not all proteins make good emulsifiers
Can strengthen a normal emulsion system
Foams- trapping gas bubbles in a viscous medium
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Protein is usually soluble
Air bubble size is critical (nebulized air)
Duration and shear rate
Temperature and physical kinetics
Food ingredient interactions (i.e. salt, acid, and lipids)..bad.
Metal ions, hydrocolloids, and sugar can increase stability
Enzymes
Enzyme Influencing Factors
 Temperature-dependence of
enzymes
 Every enzyme has an optimal temperature for
maximal activity
 The 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 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 slower enzyme reactions
Ionic Strength
 Some ions may be needed by active sites on the
protein (salting in)
 Ions
may be a link between the enzyme and substrate
 Ions change the surface charge on the enzyme
 Ions may block, inhibit, or remove an inhibitor
 Others, enzyme-specific
Common Enzymes in Foods
 Polyphenol oxidase
 Plant
cell wall degrading enzymes
 Proteases
 Lipases
 Peroxidase/Catalase
 Amylase
 Ascorbic acid oxidase
 Lipoxygenase
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
The “Raw Foods” Movement

Enzymes present in raw foods help in digesting the foods we eat

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Cooking destroys food enzymes forcing the body to produce
more of its own digestive enzymes
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Eating these enzymes saves your both the work.
Our body has a finite amount of enzyme producing potential

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But they have to enter the digestive system.
The more enyzmes we eat, the more we preserve health and longevity
Our digesting enzyme potential can be exhausted.
Enzymes in raw food also carry our "life force"

When our ability to produce digestive enzymes is exausted, we die.
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


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)

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.
Worthington Enzyme Manual
http://www.worthingtonbiochem.com/index/manual.html
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
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
Enzyme Commission
Enzyme Nomenclature
 International Union
of Biochemistry and
Molecular Biology (IUBMB)
 International Union of Pure and Applied
Chemistry (IUPAC)
 Joint Commission on Biochemical Nomenclature
(JCBN)
 IUPAC-IUBMB-JCBN
 http://www.chem.qmul.ac.uk/iubmb/enzyme/
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
How Glucose Oxidase + Catalase Works:
GO
Reaction 1: Glucose + O2
Gluconic acid + H2O2
CAT
Reaction 2:
H2O2
H2O + 1/2 O2
GO/CAT
Reaction 3: Glucose + 1/2 O2
Gluconic acid
1. Oxidoreductases: PEROXIDASE (POD)
Donor: Hydrogen peroxide oxidoreductase

Iron-containing enzyme. Has a heme
prosthetic group
N
N
Fe
N
N

Thermo-resistant – denaturation at ~ 85oC

Since is thermoresistant - indicator of proper blanching
(no POD activity in properly blanched vegetables)
1. Oxidoreductases: Catalase
Hydrogen peroxide oxidoreductase
 Catalyzes conversion of 2 molecules of H2O2 into
water and O2:
H2O2 -------------------



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: LIPOXYGENASE
H
H
……..
H
………
C
C
C cis
cis
C
H
H
+ O2
H
H
H
H
C
C
C
C
cis
H
C
trans
……..
OOH
Oxidation of lipids with cis, cis groups into conjugated cis, trans hydroperoxides.
ENZYMES are useful in analysis because of
their specificity
Reaction affected by pH, time, temperature,
substrate concentration, activators,
inhibitors
or other simple sugars
D-GLUCOSE/ D-FRUCTOSE / D-SORBITOL
Enzymatic Determination of Starch
glucose

fructose
ADP
HEXOKINASE
HEXOKINASE 
ATP
glucose-6-P
NADP+
G-6-P dehydrogenase
fructose-6-P
NADP+
PGI
NADPH
NADPH
glucose-6-P
gluconic acid-6-P
365nm
365nm
PGI = phosphoglucoisomerase

PRINCIPLE
Starch is hydrolyzed
into glucose units
by enzymatic
conversion
D-glucose can then
be quantified by
enzymatic methods
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
Worthington Enzyme Manual
http://www.worthingtonbiochem.com/index/manual.html
Functional Proteins
Protein Functionality
 Hydrodynamic-Aggregation
 Viscosity,
Elasticity, Viscoelasticity
 Solubility, Water holding capacity
 Hydrophobic Emulsion
Surface Active
and foam stabilization
 Flavor binding
Dilute
Concentration
Semi-dilute
Hydrodynamic Functionality
Viscosity

A property of liquids
 Viscosity is the resistance to flow. The amount of
energy you need to expend to get a given flow
rate.
 Stress (force per unit area) is proportional to rate
of strain (i.e., flow rate)
 Particles of any type in a fluid will increase its
viscosity
 Large, well hydrated polymers contribute most to
viscosity
Elasticity

A property of solids
 Elasticity is the force to achieve a given
percentage change in length
 Stress (force per unit area) is proportional to strain
(fractional deformation)
 An elastic material must have some solid-like
network throughout the structure
 The more load bearing structures the more elastic
 The more inter-structure links the more elastic
Viscoelasticity
 Many
materials simultaneously show solid
and liquid like properties
 If they are stretched they will partly and
slowly return to their original shape
 Elastic
solids would completely recover
 Viscous liquids would retain their shape
Water Binding

Gels contain pores
 Water can flow out of
the pores
 If the gel contracts it
may expel liquid
SYNERESIS
 Due to closer
association of protein
with protein
Solubility
Emulsoid
100
Solubility /%
80
60
40
Suspensoid
20
0
1
2
3
4
5
pH
6
7
8
Whey vs. Casein

Dense, ordered
globular proteins

Loose, disordered,
flexible chains

2D Gel

Loop-train-tail model
Practical Applications
A quick stroll through the literature…
WH= whole hydrolysate
Story Behind the Story
 Amy-Acrylamide
 Andrea-Maillard
ingredients
Effect of Citric Acid and
Glycine Addition on
Acrylamide and
Flavor in a Potato Model
System
Class discussion;
Bianca and Cassie
A quick review
Protein Analysis Methods