Starches and cereals
Starches and cereals outline
• Starch
– Source
• Amylose
• Amylopectin
• Starch Cookery
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Dextrinization
Gelatinization
Retrogradation
Effect of other ingredients
Starches and cereals outline
• Modified food starches
• Cereals and grains
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–
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Introduction
General cookery
Rice
Oats
Corn
Barley
Wheat
Grain anatomy
Bran -- contains much of the fiber
and minerals of the grain
Germ -- the part of the grain that would
become the new plant if the seed were
planted. High in protein and fat.
Endosperm -- approximately 80%
starch and 20% protein. Source of
flour and starch.
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
Potato starch granules under
polarized light
Hilum -where synthesis
of the granule
began
Image courtesy of Univ. of York, Inst. For Applied Biology
(www.york.ac.uk/org/macromol/)
Corn starch granules
Unmodified corn
starch
Corn
Potato
Tapioca
Oat
Rice
Wheat
Other
starches
(Magnification =
1000x)
Amylose molecule
CH2OH
=
O
H
OH
H
D-glucose
H
OH
HO
H
OH
Amylopectin molecule
CH2OH
O
H
=
OH
H
H
OH
HO
H
OH
D-glucose
Amylopectin (again)
Note highly branched
structure
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
Starch cookery
• To avoid lumping, disperse starch in
– Cold liquid
• Then add to hot liquid
– Fat
• Form a roux
• Roux = flour + butter + heat
– Other dry, granular ingredients
• e. g., sugar
Starch cookery
• To avoid starchy taste
– Reach gelatinization temperature, then cook
an additional 1-3 minutes on direct heat or
10-15 minutes in a double boiler
Starch cooking medium
• Dry heat
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Dextrinization
Thermal degradation of starch
Browning occurs
Such starches produce thin cooked pastes
Little thickening power, e.g., brown gravy
Starch cooking medium
• Moist heat
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Gelatinization
Starch granule swelling
Loss of amylose from the swelling granule
Gelatinization temperature depends on the
type of starch
– Produces a thick cooked paste
– Gelation (gel formation) occurs on cooling,
but this may depend on the type of starch
Gelatinization
• Swelling and disorganization of starch
granules heated in water
• Measures of gelatinization
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Swelling of granules
Increased viscosity (thickness)
Increased translucency
Increased solubility
Gelatinization temperature
Starch
Range (degrees C)
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.
Starch gelatinization
Raw
starch
Amylopectin
Heat and water
+
Swollen starch
Also see www2.hawaii.edu/lynn/main.html
Amylose
Starch gelation
swollen
amylose
collapsed
cool
Junction zone
Water
Water
Water
Starch gel
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
Starch over-retrogradation
(uglification)
Small
Large junction zones
Factors affecting gelatinization,
retrogradation, and gel formation
• Sugar
– Competes for water and plasticizes junction
zones; decreases gelatinization and gel
strength
• Acid
– Hydrolysis of acid sensitive glycosidic
linkages produces smaller pieces of starch
molecules; decreases gel strength
Factors affecting gelatinization,
retrogradation, and gel formation
• Stirring/shearing
– Collapses swollen granules; this decreases
gel formation and gel strength
• Lightning quiz
Modified starches
• Waxy
– All amylopectin, no amylose
• Pregelatinized
– Cold water dispersible (instant puddings)
• Acid modified (thin boiling)
– Limited hydrolysis of starch
– Decreases maximum viscosity
– Gives excellent cooled gel strength, e.g. gum
drop texture
Modified starches
• Cross-linked
– Restricts granule swelling
– Limits maximum viscosity
– Makes granules much less fragile
• Derivatized
– Ethers or esters
– Used to prevent or control syneresis. Good
for freeze-thaw stability
Starch-based sauces
Type
Liquid (cups)
Flour (T)
Very thin
1
1/2
Thin
1
1
Medium
1
2
Thick
1
3
Very thick
1
4
Cereals and grains
• These are seeds of the grass family
Bran -- contains much of the fiber
and minerals of the grain
Germ -- the part of the grain that would
become the new plant if the seed were
planted. High in protein and fat.
Endosperm -- approximately 80%
starch and 20% protein. Source of
flour and starch.
Cereals and grains
• Grains are economical sources of
carbohydrate energy
• The protein is relatively low in biological
value relative to meat, fish, eggs, and
milk
Grain enrichment
• Most grain foods are enriched
• This means the following are added
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Iron
Thiamin
Riboflavin
Niacin
Folic acid
General cereal cookery
• Whole grain
– Add dry cereal slowly to boiling water
• Ground cereals
– Pre-soak the cereal in cold water, then add
boiling water. This will prevent lumping of
finely ground cereals like farina (Cream of
Wheat)
Cereal expansion on cooking
• Be aware of grain expansion
• Normally this is 2-4 times the original
volume
• Pre-cooked cereals expand less than nonpre-cooked cereals
– Converted rice ---------> 4x expansion
– Minute rice --------------> 2x expansion
Rice expansion
Uncooked
Cooked
More expansion
Rice
• Brown
– Whole rice, bran intact
– Longer cooking time due to slow water penetration
of bran (up to 50 minutes)
– Brown rice has a different texture, more nutrients,
and more fiber than other forms of rice
– As of July 2008, can make the label health claim
“Diets rich in whole grain foods and other plant
foods and low in total fat, saturated fat and
cholesterol may reduce the risk of heart disease and
some cancers.”
Rice
• Polished
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Bran removed
Removes some nutrients and fiber
3x expansion on cooking
Usually enriched
• Converted
– Parboiled before bran removal
– Theory says that this treatment retains more
nutrients than polished rice. Usually enriched.
Effect of parboiling and
milling
Bran
M
M
Endosperm
M
M
M
Mineral/100g rice
Polished
Converted
Calcium
28 mg
55 mg
Iron
0.80 mg
0.74 mg
Magnesium
25 mg
27 mg
Phosphorus
115 mg
156 mg
Potassium
115 mg
187 mg
Sodium
5 mg
3 mg
Zinc
1.09 mg
1.04 mg
Copper
0.220 mg
0.267 mg
Manganese
1.088
1.110 mg
Selenium
15.1 mcg
23.9 mcg
Taken from the USDA National Nutrient Database
Rices
Rice
• Minute
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Pre-cooked polished or converted
5 minutes cooking time
2x expansion
Different taste and texture compared to other rices
• Wild
– Seeds of other grasses, but not a real rice
– Usually quite expensive
Oats
• Nutritionally quite good
• Contains a fiber that lowers circulating and
liver cholesterol
• Allowed to make heart healthy claims on the
box
– Rolled oats --crushed and flattened between rollers
– Oatmeal -- ground oats, common breakfast cereal
Corn
• White and yellow types
– Native American grain
• Hominy
– Alkaline treated corn
– Grain swells and produces a distinctive
flavor
– May be whole grain and canned, or dried
and ground to a meal
Corn
• Grits
– Coarsely ground corn
• Meal
– Finely ground corn
– Meal can be used to make corn bread or can
be converted into corn starch and corn syrup
• Flakes
– Rolled, dried, and toasted grain
Barley
• Used in soups and baby foods
• Useful for people who have allergies to
other grains (especially wheat)
• Food and Drug Administration (FDA)
announced (1/9/06) that whole-grain
barley and barley-containing products
are allowed to claim that they reduce the
risk of coronary heart disease (CHD)
Wheat
• Wheat has a problem which it shares
with many other grains
• Low in the essential amino acid L-lysine
• The wheat-rye cross triticale is sufficient
in L-lysine
Wheat
• Farina
– Cream of wheat
– Finely ground wheat which has been
enzymatically treated to degrade some of the
protein and make cooking quicker
– Used as a thickener in foods or eaten as a
breakfast cereal
Wheat
• Durum
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Very high protein flour
Said to be “hard”
Usually finely ground
Only used for pasta
• Semolina
– Coarsely ground durum
Wheat nomenclature
Growing
season
Spring, winter -------------------
Grain pigment
White
Red
Low protein
High protein
Kernel texture
Hard
Soft
High protein
Low protein
Wheat proteins
• A hard red spring wheat would be high in
(functional) proteins while a soft white winter
wheat would be low in functional proteins
• Wheat protein contributes structure
• Different flours (protein contents) are used for
different products (cakes, breads, etc.) in order
to produce the proper texture
• Lightning quiz