starches and cereals

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.

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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