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Starches and cereals
Starches and cereals outline
• Starch– Source
• Amylose• Amylopectin
• Starch Cookery– Dextrinization– Gelatinization– Retrogradation– Effect of other ingredients
Starches and cereals outline
• Modified food starches• Cereals and grains
– Introduction– General cookery– Rice– Oats– Corn– Barley– Wheat
Grain anatomy
Bran -- contains much of the fiberand minerals of the grain
Endosperm -- approximately 80%starch and 20% protein. Source offlour and starch.
Germ -- the part of the grain that wouldbecome the new plant if the seed wereplanted. High in protein and fat.
Starch granulesSynthesized in the amyloplasts
Birefringence indicates that the granules are semi-crystalline
Interior structure of the granules is still not well understood
Normal light Polarized light
Image courtesy of Univ. of York, Inst. For Applied Biology(www.york.ac.uk/org/macromol/)
Potato starch granules under polarized light
Hilum --where synthesisof the granulebegan
Corn starch granules
Unmodified cornstarch
Other starches
(Magnification =1000x)
Corn Oat
Potato Rice
Tapioca Wheat
Amylose molecule
=O
OHH
HH
OHOH
H OH
CH2OH
D-glucose
Amylopectin molecule
=
O
OHH
HH
OHOH
H OH
CH2OH
D-glucose
Amylopectin (again)
Note highly branchedstructure
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– 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– 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– 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 typeof starch, that is for each botanical source.
+
Starch gelatinization
Heat and waterRaw starch
Swollen starch Amylose
Amylo-pectin
Also see www2.hawaii.edu/lynn/main.html
Water
WaterWater
Starch gelation
swollencollapsed amylose
coolJunction zone
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)
Large junction zonesSmall
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 fiberand minerals of the grain
Germ -- the part of the grain that wouldbecome the new plant if the seed wereplanted. High in protein and fat.
Endosperm -- approximately 80%starch and 20% protein. Source offlour 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
– 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 non-
pre-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– 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.
M M
MMM
Effect of parboiling and milling
Bran
Endosperm
Mineral/100g rice Polished ConvertedCalcium 28 mg 55 mgIron 0.80 mg 0.74 mgMagnesium 25 mg 27 mgPhosphorus 115 mg 156 mgPotassium 115 mg 187 mgSodium 5 mg 3 mgZinc 1.09 mg 1.04 mgCopper 0.220 mg 0.267 mgManganese 1.088 1.110 mgSelenium 15.1 mcg 23.9 mcg
Taken from the USDA National Nutrient Database
Rices
Rice
• Minute– 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– 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
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