O
Starch
O
Plant cell amyloplasts (leucoplasts)
Vacuole
Middle
lamella
Amyloplast
O
Leucoplasts (amyloplasts)
1
O
Leucoplasts (amyloplasts)
Blue, purple, or black potato amyloplasts have been
stained with iodine
O
Leucoplasts (amyloplasts)
Potato amyloplast containing a starch granule. Note
growth rings.
O
Starch granules
Synthesized in the amyloplasts
Normal light
Polarized light
Birefringence indicates that the granules are semicrystalline
Interior structure of the granules is still not well
understood
2
O
Starch granules (normal light)
„
„
„
These are sorghum
starch granules
Note both smooth
and angular surfaces
Granules are
composed of two
molecules, amylose
and amylopectin
O
Selected starch granules
Amaranth (bar = 1 µM)
Corn (bar = 10 µM)
Potato (bar = 50 µM)
Rice (bar = 2 µM)
O
Potato starch granules
under polarized light
Hilum -where synthesis
of the granule
began
3
O
Starch granules
Birefringence indicates semi-crystalline
nature of the starch granule
„ Granule contains both polycrystalline
(highly organized) regions and
amorphous (unorganized) regions
„
O
Starch crystallinity
„
Cereal starches - type A x-ray pattern
–
„
Tuber/root starches - type B x-ray
pattern
–
„
Parallel double helices separated by
interstitial water
Similar to type A structure except that a
column of water replaces one of the starch
double helical structures
Type B can be converted into type A but
not vice versa
O
Amylopectin
Alpha-1,6
Highly branched polymer of D-glucose
Much higher molecular weight than amylose
4
O
Amylopectin
Starts out as a single D-glucopyranosyl
unit attached to a protein, amylogenin
„ Glucoses are added sequentially by
donation from ADP-glucose
„ Branching enzymes are required to
produce the branched structure
„
–
These enzymes require a linear chain of 4050 units before transferring a portion of the
chain which becomes the branch
O
Amylopectin
Branch points comprise 4-5% of the total
linkages
„ A, B, and C chains comprise the molecule
„ Some, if not most, of the branches exist as
double helices of parallel chains
„
O
A, B, and C chains
A chain
B chain
ϕ
C chain
Reducing end
5
O
Amylopectin
Note highly branched
structure
Reducing end
O
Amylopectin
For potato starch, DPs of B chains is 3445 and 23-32
„ For potato starch, DPs of the A chains is
13-15
„ Representative molecular weights range
from 107 to 5 x 108
„ These are among some of the largest
molecules in nature
„
Phosphate esters
in potato starch
O
Potato amylopectin is unique due to
having phosphate esters
„ 1 phosphate every 200-550 Dglucopyranosyl units
„ Phosphate groups located near branch
points, mostly at O-6
„ Most phosphates are on B chains
„ Potato starch pKa = 3.7
„
6
O
Location of phosphate esters
Phosphate ester substitution
occurs in this area
O
Phytoglycogen
Similar to amylopectin but more highly
branched
„ 10% of all linkages are branch points
„ Occurs in sweet corn up to 25% by
weight
„ Water soluble
„
O
Amylose
Alpha-1,4
A linear polymer of D-glucose (actually it is now
known that amylose contains a few short and
very widely separated side chains)
Much lower in molecular weight than amylopectin
Average molecular weight ≅ 106
7
O
Amylose
However, many amylose molecules have
a few branches (0.3-0.5% of the total
linkages)
„ Branches are either very long or very
short
„ Thus, molecules behave as essentially
linear
„ Linear molecules retrograde easily and
form strong films
„
O
Amylose
α-D-1→4 linkages produces a right
handed helix
„ Helical nature of amylose causes amylose
films and fibers to be more elastic than
those of cellulose
„ Helix exterior is hydrophilic and interior
is hydrophobic
„
–
Lipophilic molecules can be complexed in
the amylose interior
O
Amylose-lipid complexes
The lipid inserts itself into the hydrophobic interior of the
amylose helix. Non-waxy cereal starches contain about
0.6-1.2% total lipid. Waxy maize contains about 0.2%.
8
O
Amylose-lipid complexes
Lipids may be intentionally added to
baked goods to increase their shelf life
„ Such lipophilic compounds include
„
Glyceryl monopalmitate (GMP)
Sodium steroyl lactylate (SSL)
–
–
O
GMP and SSL
„
These surfactants affect starch systems
by
Affecting starch gelatinization and pasting
Modifying the rheological behavior of the
resulting pastes
Inhibiting the crystallization of starch
molecules associated with retrogradation
–
–
–
O
GMP and SSL
O
CH3
O
HO
GMP
OH
Na
O
O
O
O
H3C
O
CH3
O
CH3
0-4
SSL
9
O
Corn amylose characteristics
Number average DP = 930-990
„ Weight average DP =2270-2550
„ Average number of chains per molecule =
5.3
„
–
Takeda, Starch 40 (1988) 51
O
Amylose/amylopectin ratio
Generally, about one part amylose to
every three parts of amylopectin for
“normal” grain sources
„ “Waxy” varieties contain 0% amylose
and 100% amylopectin
„
–
Used in non-gelling starch applications,
starch-thickened frozen products, and many
modified starches
O
Amylose/amylopectin ratio
„
High amylose varieties
–
–
50-70% amylose, the rest is amylopectin
Useful as binders and film formers
10
O
Starch degrading enzymes
Beta amylase--an exo enzyme
Maltose
Maltose
Beta-amylase
AP
Maltose
Limit dextrin
phosphorylase
glucoamylase
D-glucose
O
Starch degrading enzymes
„
Endo enzymes
–
–
–
Attack interior of the molecule
May attack AP on either side of a branch
point
Example: alpha-amylase
O
Debranching enzymes
Alpha 1,6 branch point
Amylopectin
R enzyme (malted barley)
Pullulanase
Isoamylase (yeast)
11
O
Cyclodextrins
Produced from starch by the action of
cyclodextrin glucanotransferase from
Bacillus sp.
„ Rings of 6, 7 or 8 D-glucopyranosyl units
„ Also called Schardinger dextrins
„ Hydrophilic exterior and hydrophobic
interior
„
O
Cyclodextrins
N=6
N=7
N=8
O
β-Cyclodextrin
12
O
Cyclodextrin model
Hydrophobic
interior
Hydrophobic molecules can be complexed in the interior
of these molecules and form clathrates
O
Potential uses of cyclodextrins
Stabilization of volatile essential oils
„ Removal of bitter components of citrus
juices
„ Not yet approved for use in foods in the
US
„
O
Gelatinization
Swelling and disorganization of starch
granules heated in water
„ Measures of gelatinization
„
–
–
–
–
–
–
Swelling of granules
Increased viscosity
Increased translucency
Increased solubility
Loss of birefringence
Increased susceptibility to enzymes
13
O
Gelatinization temperature
Starch
Range (oC)
Potato
56-66
Corn
62-72
Sorghum
68.5-75
Wheat
52-63
Gelatinization temperature range is characteristic for
each type of starch, that is for each botanical source.
O
Starch gelatinization
Heat and water
Raw
starch
Amylopectin
+
Amylose
Swollen starch
O
Gelatinization micrographs
Unmodified corn
starch
Corn starch, 65 C
14
O
Gelatinization micrographs
Corn starch, 70 C
Corn starch, 85 C
O
Gelatinization
„
This energy requiring process can be
followed by differential scanning
calorimetry (DSC)
O
Endothermic Heat Flow
DSC and gelatinization
Tg
(glass
transition
temperature)
40
Tm2 (melting
endothem of the
lipid-amylose complexes)
Tm1 (initial melting
endotherm)
60
80
100
120
Temperature oC
140
160
15
O
Brabender amylograph
O
Brabender amylograph
Peak
viscosity
Viscosity
Breakdown
Cooled paste
stability
Setback
Time/temperature
O
Amylographs of different starches
Corn
Cross-linked
Viscosity
Waxy corn
Time/temperature
16
O
Starch gelation
swollen
Junction zone
collapsed
cool
amylose
water
water
water
Starch gel
O
Starch gelation
Amylose is the “glue” that holds the gel
together
„ Therefore, waxy starches do not gel
„
–
They form thick, cooked pastes and are
frequently the starting material in the
production of modified food starches
O
Starch retrogradation
Junction zones;
not too large
17
O
Starch over-retrogradation
(uglification)
Large junction zones
O
Starch Gelatinization
O
Starch granules contain both linear amylose
and branched amylopectin.
18
O
Raw, uncooked starch granules
O
O
Notice loss of amylose from the granules
19
O
Some granules have collapsed.
O
Gelation
O
Now we start to cool.
20
O
Notice areas of association. These are
called junction zones.
O
This picture is not yet complete as we haven’t
accounted for the water in the system.
O
water
water
water
water
water
water
This is a starch gel
21
O
Uglification
O
WATER
This picture ignores swollen and collapsed
granules.
O
WATER
+ WATER of SYNERESIS that has been
squeezed out of the gel structure
The texture gets very ugly when this happens.
22
O
Retrogradation
Retrogradation = gelation + uglification
„ Amylose retrogrades much more rapidly
than amylopectin
„ Staling of baked goods and loss of
viscosity and precipitation in soups and
sauces is at least partially related to
retrogradation
„
O
General starch uses
To produce viscous pastes and softtextured gels
„ In some products, the extent of
gelatinization may be quite low (10%)
„
–
„
Cookies and pie crusts
In others it may be nearly complete
(96%)
–
Cakes and breads
O
Factors affecting gelatinization,
retrogradation, and gel formation
„
Sugar
–
„
Competes for water and plasticizes junction
zones; decreases gelatinization and gel
strength, increases gelatinization
temperature
Acid
–
Hydrolysis of acid sensitive glycosidic
linkages produces smaller pieces of starch
molecules; decreases gel strength
23
O
Factors affecting gelatinization,
retrogradation, and gel formation
„
Polar lipids retard gelatinization
–
„
Form complexes with amylose
Stirring/shearing/pumping
–
Collapses swollen granules; this decreases
gel formation and gel strength
O
Starch hydrolysis
„
Mild acid treatment produces acidmodified or thin-boiling starches
–
„
Only a few glycosidic bonds are hydrolyzed
in this procedure
More extensive hydrolysis produces
dextrins
–
–
–
Classified by their dextrose equivalency (DE)
DE = 100/DP
Dextrin DP ≥ 100
O
Dextrin uses
Film formers
Adhesives
„ Coating agents
„ Humectants
„ Bulking agents
„ Crystallization inhibitor
„ Fat replacer
„
„
24
O
Dextrin types
Corn syrup solids: DE 20-60
„ Maltodextrins: DE < 20 (DP 5-100)
„ Corn syrups (glucose syrups): DE > 20
(DP < 5)
„
O
Corn syrup solids
These dissolve rapidly in water and are
mildly sweet
„ They find uses in many processed foods
„
O
Maltodextrins
Prepared by acid or enzyme (α-amylase)
treatment
„ These are bland, non-sweet bulking
agents
„ Selected uses
„
–
Dry powder mixes, coffee whiteners, bakery
products, confections, frozen foods
25
O
Corn syrups
Produced by extensive acid or enzyme
hydrolysis
„ A syrupy mixture of D-glucose, maltose,
maltooligosaccharides, and a few acid
reversion products
„ Uses
„
–
Imitation pancake syrup
Glucose and
fructose production
„
Glucose
–
–
„
O
Add thermally stable α-amylase to starch
and jet cook
Later treatment with glucoamylase,
concentration, and crystallization will
produce D-glucose
Fructose
–
–
Treat D-glucose with glucose isomerase
Equilibrium: D-glucose, 58%; D-fructose,
42%
O
Modified starches
„
Waxy
–
All amylopectin, no amylose
26
O
Modified starches
„
Pregelatinized (prepasted)
–
–
Starch is cooked and roll dried
Modified or unmodified starches may be
used to make pregelatinized products
„ Cold
water dispersible (instant puddings, instant
soups, extruded snacks, pizza topping, cookies,
bakery fillings)
„
Nomenclature note: Non-pregelatinized
starches are called cookup starches
O
Modified starches
„
Cold-water-swelling starch
–
–
„
Heat corn starch in 75-90% ethanol to 150175oC for 0.5-2.0 hours
This product swells extensively in room
temperature water
Uses
–
–
Gum candy
Muffin batters (containing blueberries)
O
Modified starches
„
Acid modified (thin boiling)
–
–
–
Limited hydrolysis of starch
Decreases maximum viscosity
Gives excellent cooled gel strength, e.g. gum
drop texture
27
O
Modified starches
Cross-linked
„ Usually employs phosphorylating
reagents or adipic acid
„
–
–
–
Restricts granule swelling
Limits maximum viscosity
Makes granules much less fragile to high
temperature, extended cooking times, low
pH, and high shear
O
Distarch phosphates
Reaction of starch with phosphoryl
chloride or sodium trimetaphosphate in
an alkaline slurry
„ Very low levels of derivatization are
necessary to produce the desired effect
(less than 1 crosslink per 1000 glucoses)
„ Brabender amylographs of cross-linked
starches are quite different
„
O
Crosslinked uses
Extruded foods
Canned foods
„ Spoonable salad dressings
„ Canned soups
„ Canned gravies
„ Canned puddings
„ Batter mixes
„
„
28
O
Crosslinked, stabilized uses
Baby foods
„ Frozen fruit pies
„ Pot pies
„ Gravies
„
O
Modified starches
„
Derivatized (or stabilized)
–
–
Ethers or esters
Used to prevent or control syneresis. Good
for freeze-thaw stability
O
Starch acetates
Max DS allowed = 0.09
Lowers gelatinization temperature
„ Improves paste clarity
„ Increases peak viscosity
„ Improves freeze-thaw stability
„
„
29
O
Starch phosphate monoesters
Dry starch in the presence of
phosphorylating agents
„ Max DS allowed = 0.002
„ Long, cohesive pastes
„ Lowers gelatinization temperature
„
O
Starch alkenylsuccinates
„
React starch with anhydride
–
–
–
–
Compatible with fat or oil because of
hydrophobicity
Emulsifier
Emulsion stabilizer
Uses
„ Pourable
dressings
beverages
„ Partial fat replacement
„ Flavored
O
Starch alkenylsuccinates
O
Starch---OH
H3C
+
O
O
O
CH3
Starch---O
OH
O
30
O
Starch ethers
React starch with propylene oxide to
produce hydroxypropylstarch
„ DS 0.02-0.2 (max DS = 0.2)
„ Lower gelatinization temperature
„ Clear pastes
„ Good freeze-thaw stability
„
O
Starch ether uses
Thickeners
„ Extenders
„ Coffee whiteners (low molecular weight
products)
„
Reasons for making
modified starches
„
O
To
–
–
–
–
–
Decrease setback
Provide freeze-thaw and cold storage
stability
Provide high temperature stability
Provide acid stability
Decrease syneresis
31
Reasons for making
modified starches
„
To
–
–
–
–
–
–
Increase or decrease viscosity
Improve paste of gel texture
Improve paste clarity and sheen
Increase water binding
Decrease or increase gel formation
Decrease gel temperature
Reasons for making
modified starches
„
O
To
–
–
–
–
Increase or decrease gel strength
Decrease or increase cooking temperature
Increase shear stability
Improve coating characteristics
Reasons for making
modified starches
„
O
O
To
–
–
–
–
Improve adhesion
Improve extrudability
Make cold-water soluble or swelling
Introduce hydrophobic groups
32
O
Starch modification processes
„
Chemical reactions
–
–
–
–
Esterification
Etherification
Oxidation
Depolymerization (thinning)
„ Acid
catalyzed
+ base
„ Oxidation
–
Transglycosylation + depolymerization
„ Dextrinization
with catalyst
O
Starch modification processes
„
Heat treatments
–
–
–
„
Pregelatinization
Dextrinization (w/o catalyst)
Cold-water-swelling processes
Genetic modifications
O
Reactions currently
allowed and used in the US
„
Esterification
–
–
–
–
–
–
–
Acetic anhydride
Acetic/adipic mixed anhydride
1-octenylsuccinic anhydride
Phosphoryl chloride
Sodium trimetaphosphate
Sodium tripolyphosphate
Monosodium orthophosphate
33
O
Reactions currently
allowed and used in the US
„
Etherification
–
Propylene oxide
„
Acid modification
„
Bleaching
–
–
–
–
–
Hydrochloric and sulfuric acids
Hydrogen peroxide
Peracetic acid
Potassium permanganate
Sodium hypochlorite
O
Reactions currently
allowed and used in the US
„
Oxidation
–
„
Sodium hypochlorite
Various combinations of these reactions
O
Derivatives used in
modified food starches
„
Crosslinked starches
–
–
„
Distarch phosphate
Distarch adipate
Stabilized starches
–
–
–
–
Hydroxypropyl ether
Acetate
Octenylsuccinate half ester
Monostarch phosphate
34
O
Derivatives used in
modified food starches
„
Crosslinked and stabilized starches
–
–
–
–
Hydroxypropylated distarch phosphate
Phosphorylated distarch phosphate
Acetylated distarch phosphate
Acetylated distarch adipate
O
Crosslinking reaction
–
–
–
–
–
–
–
–
–
Modifies cooking characteristics
Increases viscosity and body
Inhibits swelling
Improves heat and acid stability
Improves shear tolerance
Reduces cohesiveness
Inhibits gel formation
Reduces setback
Improves gel clarity
O
Stabilizing reaction
Increases cold storage and freeze-thaw
stability
„ Reduces energy required to cook
„ Improves clarity and sheen
„ Inhibits gel formation
„ Reduces setback, gel formation, and
syneresis
„ Increases peak viscosity
„
35
O
Octenylsuccinylation
Provides emulsifying properties
„ Improves emulsion stabilizing properties
„ Provides water resistance to films
„ Improves flow properties of dry starch
„
O
Pregelatinization reaction
„
Produces cold-water hydration and
solubility
O
Acid thinning reaction
Reduces hot- and cold-paste viscosity
Reduces energy required to cook
„ Increases tendency to gel
„ Retains gel properties
„
„
36
O
Oxidation reaction
Improves color
„ Reduces energy required to cook
„ Reduces hot-paste viscosity
„ Reduces gel formation
„ Increases paste stability
„ Improves adhesion in breading and
coating functions
„
O
Heat reactions
„
Dry
–
–
„
Reduces viscosity
Reduces energy required to cook
Wet (but without pasting)
–
Makes possible granule swelling in cold
water
O
Ways starches are used
„
Dry, intact granules
„
Swollen granules
–
–
–
Tableting, dusting, molding
Provide viscosity and texture
Hold water
„
Disintegrated granules
„
Precooked granules
–
–
Film formation
Provides “instant” viscosity
37
Benefits of modified
starches in foods
„
Adhesion
–
Batters and breadings
„
Binding
„
Encapsulation
„
Gelation
–
–
–
Processed meats
Flavors
Puddings, cream fillings, gelled candies
Benefits of modified
starches in foods
„
O
Moisture retention
–
Baked goods
„
Suspension
„
Texturization
–
–
„
O
Beverages
Fruit fillings
Thickening
–
Soups, sauces, gravies, batters, etc.
O
Typical foods
containing modified starches
Soups
Sauces
Gravies
Salad dressings
Puddings
Frozen desserts
Pet foods
Processed meats
Baked goods
Condiments
Frostings/glazes
Fruit fillings
Batters/breadings
38
O
Variables to consider
in choosing a modified starch
Application
„ Other ingredients
„ Processing conditions
„ Final consistency
„ Finished product attributes
„ Other considerations
„
O
Application
Canned product
„ Frozen product
„ Instant product
„ Emulsion
„ Shelf-stable product
„ Heat-and-serve product
„
O
Application
Microwavable
Bakery product
„ Extruded product
„ Dehydrated product
„ Encapsulated flavor
„
„
39
O
Other ingredients
Water
Fat/oil
Emulsifier
Sugar
Acid (pH)
Gums
Proteins
Flour
Salt
O
Processing conditions
Processing and storage temperatures
„ Times at each processing and storage
temperature
„ Shear
„
O
Final consistency
Firm, rigid gel
Soft gel
„ Liquid (viscosity)
„
„
40
O
Finished product attributes
–
–
–
–
–
–
–
–
–
Texture
Flavor
Clarity
Sheen
Color
Freeze-thaw stability
Room-temperature shelf life
Refrigerated shelf life
Dry mix attributes
O
Other considerations
Legality/regulatory
„ Economics
„ Marketing target
„ Existing products
„ Ethnic preferences or requirements
„ Allergens
„
O
Starch manufacture
41
O
Starch manufacture
Corn
Steep (SO2, pH 3-4, 48-52oC,
30-40 hours
Germ separation
hydroclone
Germ
Endosperm and fiber
Grind and filter
Endosperm
Fiber
centrifuge
Starch
Protein
O
Corn milling
42