Starch Flashcards
what is starch
characteristics?
complex carbohydrate that consists of two fractions: amylose and amylopectin
this large polymer of glucose is slightly soluble
serves as a thickener
Amylose vs Amylopectin
AMYLOSE
▪ Linear,1,4-α-glucosidic
linkages
▪ Loose, flexible coil.
▪ Amount varies with food
product (~17-30%).
▪ Iodine can be trapped in helix.
▪ Test shows blue color.
AMYLOPECTIN
▪ Dendritic (branched chain)
▪ Lacks helical configuration
▪ More abundant (some foods
may contained up to 80%)
▪ Iodine not trapped in structure.
▪ Test shows purple-red color.
root 80% cereal 75% composition
Starch Granule
composed of amylose and amylopectin molecules.
Granules are made in leucoplasts, plastid in the cytoplasm of plant cells
Each granule consists of concentric lay- ers of amylopectin molecules interrupted by some amylose molecules, which often are arranged in a somewhat organized manner within the layers (growth rings)
the mol- ecules within each layer are held together simply by hydrogen bonding, and similarly, the layers are bonded together by the same secondary bonding arrangement.
Starch granules, seen
using X-ray diffraction
and polarized light, reveal
a _______ pattern that
looks like a ________
birefringence
maltese cross
Functional properties of starch
for starch to be effective as a thickening agent it must be heated with water causing gelatinization (Physical change)
if heated without water, it undergoes dextrinization (chemical change)
These processes are important in food preparation, for they
determine the behavior of starch, its thickening ability in sols, and
also its gel-forming properties.
gelatinization
physical process that occurs when starch is heated in water. Heat energy causes hydrogen bonds in the starch granules to break allowing water into the granule causing swelling. Water that enters forms h bonds with amylopectin and amylose molecules
what property of water allows it to increase the volume of the granules more and more as it it enters and forms h bonds with amylose and amylopectin?
water is not compressible
How does bound water affect the viscosity of the starch mixture during gelatinization
by increasing the granule size and reducing the amount of free water external to the granules
What is pasting and how does it relate to gelatinization?
the changes that take place in starch as it heats in the presence of water
Changes that occur in the granule when heating is continued after gelatinization has taken place
what starch reaches maximum viscosity at 20°C (68°F) lower than other starches—then begins to thin.
tapioca
Increased translucence during gelatinization is particularly noticeable in the
root starches. ex. potato and tapioca
_______ starch is far more effective than other starches as a thickening agent (Table 6.3). _____ starches are somewhat more effective than cereal starches; ____ is the least effective of the starches commonly available. ______, which is used in the home, is even less effective than pure wheat starch because of its protein content. The waxy starches are more effective thickening agents in starch pastes than are their standard counterparts
Potato
Root
wheat
Flour
Effect of sugar during gelatinization
hygroscopic nature of sugar causes it to compete with starch for water delaying gelatinization and final temperature required to
achieve gelatinization is raised.
Sugar may increase translucence, reduce paste viscosity and gel strength.
Effect of lemon juice or acid during gelatinization
If a starch has to be heated in the presence of an acid what should you do to obtain a thicker product?
The combination of acid and heat, particularly below pH 4, causes a hydrolytic reaction that begins to break down molecules of starch into slightly smaller molecules CAUSING A THINNER PASTE since these molecules move more freely
Rapid heating rate will keep the hydrolysis time to a minimum and result in a thicker product.
If sugar content is low, what should be done to causes a temporary increase in viscosity and a lower gelatinization temperature
When it is necessary to gelatinize starch in the presence
of both acid and sugar, what is imperative to ensure complete gelatinization and maximum thickening.
Increasing acid in sugar–starch mixtures
Sufficient heating
What ingredients will cause a reduction in the temperature for maximum gelatinization/viscosity of starch mixtures?
presence of fats and milk proteins
What is gelation? Explain the process
Starch pastes (sols) are converted to gels as they cool.
Amylose molecules that have left the starch granules during the gelatinization process are free to move about in a paste. The paste loses energy gradually during cooling and the free amylose molecules move more slowly as energy is lost. The gradual reduction in energy during cooling promotes the formation of hydrogen bonds between amylose molecules, with the result that frequently a starch paste is trans- formed into a gel
What is gelation affected by?
*TYPE/CONCENTRATION OF STARCH: Starches low in amylose—waxy starches—do not form gels in
concentrations normally used in food.
- EXTENT OF HEATING: For optimal gel strength, starch pastes need to be heated until enough amylose has been released.
❑ But not so much that the granules start to split apart into fragments. - AGITATION: Agitation during gelling disrupts hydrogen bonds already
formed—and weakens the ensuing gel. - OTHER INGREDIENTS:
SUGAR increases translucence of gel
ACID can cause softening of gel if in the presence of sugar, if heating rate is too slow, and if added prior to gelatinization
FATS AND PROTEINS may influence gel strength.
❑Egg yolk added to a gelatinized starch mixture must be
heated sufficiently to coagulate the yolk proteins if not a gel doesn’t form
What is syneresis?
Syneresis is the loss of liquid from a gel
as a gel ages amylose molecules draw together and water is squeezed out
What is retrogradation?
Over time, amylose molecules tend to orient themselves in
crystalline regions.
This more orderly alignment—retrogradation—is detected on
the tongue as a gritty texture
Amylopectin also participates in retrogradation, albeit at a slower rate than does amylose.
Heat energy can break these hydrogen bonds
What are the different types of native starches?
Cereal starches: oats, rice, wheat, corn, sorghum
Cereals consist of bran covering endosperm and germ
Root starches: cassava root starch, potato starch, arrowroot
Tree starches: sago starch
uses of Native starches
frequently used as thickening agents
Grains have been bred to be nearly 100 percent amylopectin— Waxy starches absence of amylose inhibits gel formation also thickening agent
High-amylose starches can be made into thin films. Suitable for wrapping items such as candies
What are modified starches
Name them.
Changes by physical/chemical to starches
1) PRE-GELATINIZED STARCHES swell to a desirable thickness when water is added—with no heating necessary.
2) COLD WATER–SWELLING STARCH (CWS) is pre-gelatinized. Well suited for use in microwave cookery.
3) THIN-BOILING STARCHES are treated with acid for hydrolytic reaction that increases the solubility of the starch and its thickening power diminishes.
thin sol when hot, strong gel when cold Ex. gum drops
4) CROSS-LINKED STARCHES minimize retrogradation, less likely to rupture retaining viscosity, effective thickeners, shows little change from temp, agitation or acid
5) STARCH PHOSPHATES increase stability and improve texture of
starch pastes thickened with them.
❑ Excellent clarity; reduced syneresis or weeping.
6) SPHERICAL AGGREGATES OF STARCH GRANULES serve as flavor carriers in food products
State how each starch can be used in food
1) pre gelatinized starch
2) cold water swelling starch
3) thin boiling starch
4) cross-linked starch
5) starch phosphates
6) spherical aggregates of starch granules
1) PRE-GELATINIZED STARCHES swell to a desirable thickness when water is added—with no heating necessary.
2) COLD WATER–SWELLING STARCH (CWS) is pre-gelatinized. Well suited for use in microwave cookery.
3) THIN-BOILING STARCHES are treated with acid for hydrolytic reaction that increases the solubility of the starch and its thickening power diminishes.
thin sol when hot, strong gel when cold Ex. gum drops
4) CROSS-LINKED STARCHES minimize retrogradation, less likely to rupture retaining viscosity, effective thickeners, shows little change from temp, agitation or acid
5) STARCH PHOSPHATES increase stability and improve texture of
starch pastes thickened wit
List the uses of starches
Starch is used in many different food products due to its ability
to thicken sauces and to bind fat.
Starches are used commercially in combination with a component such as oil, as a fat replacer.
Modified starches are used with proteins, gums, or emulsifiers
in reduced-fat and fat-free products.
Criteria for selection of starches
what type of starch for low calorie options
starches with poor freeze thaw stabilities?
useful starches for freeze/thawing?
For low-calorie options, the starch needs excellent thickening
and/or gelling capabilities mouth feel also important
Cornstarch and wheat starch have poor freeze-thaw stabilities.
❑Waxy rice flour is a useful starch for products that are to be
frozen and thawed
Name the advantages, limitation and use for each starch
1) Potato
2) Corn
3) Waxy corn
1) A: thickening, translucent
L: thins with long heating, stringy
Use: pudding
2) A: translucent, gels L: moderate thickening
Uses: puddings, pie fillings, gravy sauces
3) A: Doesn’t gel L: stringy
Uses: fruit pie filling
Name the advantages, limitation and use for each starch
4) High amylose
5) Pre-gelatinized
6) Cold water swelling
7) Phosphates
4) A: thin films L: non-traditional gel
Uses: edible films
5) A: swells w/o heat L:reduced thickening
Uses: instant foods
6) A: Improved texture, stability L: reduced thickening
Uses: microwaveable sauces/entrees
7) A: Little syneresis, non stringy, clear
Use: with waxy starches
