Transcript Cereal Grains, Legumes and Oilseeds 1211

Cereal Grains, Legumes and
Oilseeds
1211
Steven C Seideman, PhD
Extension Food Processing Specialist
Cooperative Extension Service
University of Arkansas
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Cereal Grains, Legumes and
Oilseeds
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This module covers some of the basic cereal
grains, legumes and oilseeds- their production,
composition, processing and ultimate use.
It is a brief summary of Chapter 17 “Cereal
Grains, Legumes and Oilseeds” from the book
FOOD SCIENCE by Norman N. Potter and
Joseph H. Hotchkiss. Published by Kluwer
Academic/Plenum Publishers, New York.
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Cereal Grains
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Cereals
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Cereals are plants that yield edible grains.
They are consumed worldwide and make up a
majority of the worlds calories and 50% of protein
consumption.
Rice is the world’s most important food with
wheat not far behind. Over 90% of rice is grown
in Asia where it is consumed.
In the U.S., corn is the leading grain but most is
used for animal production while wheat is used
directly for human consumption.
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Photo courtesy of USDA
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Cereal Grains
Wheat, rice and corn production worldwide
is on the order of 525 million tons annually.
 The principle cereal grains grown in the
U.S. include corn, wheat, oats, sorghum,
barley, rye, rice and buckwheat.
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Composition of Some Cereals
Grains (%)
Grain
Corn
Wheat
Oats
Rice
Moisture Carbohydrates Protein Fat
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72
10
4
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69
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2
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58
10
5
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65
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2
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Physical Characteristics of Grain
Starchy endosperm- main part of the grain
or kernel.
 Protective outer layers- bran or hull
 Embryo or germ- typically located at the
bottom of the kernel.
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Milling of Cereal Grains
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In most milling operations, the hulls are removed
which are largely indigestible by humans. The
dark-colored bran is also removed.
The germ, which is high in oil, is enzymatically
active and under certain conditions would be
likely to produce a rancid condition in the grain.
Thus, the main component of interest is the
starchy, proteinaceous endosperm.
Since the bran is rich in B vitamins and minerals,
it is a common practice to add these back to
processed grains from which they came. This is
known as “enrichment”.
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Cereal Grains
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Typically cereal grains contain a moisture of 1014% if properly dried. When the moisture content
is higher than this, they must be dried or they may
mold or rot in storage before they can be used.
Cereal grains contain about two-thirds
carbohydrate, most is in the form of digestible
starches and sugars.
The operations of milling generally remove much
of the indigestible fiber and fat from these grains
when they are to be consumed for human food.
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Wheat
Wheat is classified into one of two types –
Hard wheat is higher in protein than soft
and produces a stronger dough used for
bread-making. Soft wheat is better for
batters and cake baking.
 Wheat milling is basically a succession of
pulverizing steps to break down the
endosperm.
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Photo courtesy of USDA
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Photo courtesy of
USDA
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Photo courtesy of
USDA
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Conventional Wheat Milling
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Milling is a progressive series of disintegrations
followed by sieving. The disintegrations are made
by rollers set progressively closer and closer
together. The first rollers break open the bran and
free the germ from the endosperm. The second and
third rollers further pulverize the brittle endosperm
and flatten out the semiplastic germ. The flakes of
bran and flattened germ are removed by the sieves
under the first few sets of rollers.
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Conventional Wheat Milling
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The pulverized endosperm is run through
successive rollers set still closer together to grind
it into finer and finer flour, which is sifted under
each set of rollers to remove the last traces of
bran.
As flour is progressively milled, it becomes whiter
in color, better in bread-making quality but lower
in vitamin and mineral content.
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Uses of Wheat Flour
The uses of wheat flour in the baking
industry include the making of breads,
sweet doughs, cakes, biscuits, doughnuts,
crackers and the like.
 Another use of wheat flour and courser
milled fractions of wheat are alimentary
pastes such as macaroni, spaghetti and other
forms of noodles and pasta.
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Uses of Wheat Flour
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Alimentary pastes are mostly milled wheat flour
and water. The wheat is usually hard durum and is
milled to yield course particles called “semolina”.
Alimentary pastes may also contain eggs, salt and
other minor ingredients.
They differ from bakery doughs in that alimentary
pastes are not leavened.
Alimentary pastes are usually made with 100 parts
wheat flour/ 30 parts water, mixed, and extruded
into thin sheets, cut into noodles or other shapes
and then dried.
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Rice
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Rice is unusual compared to other grains in that it
is not ground into flours before consumption.
Worldwide, rice is primarily consumed as an intact
grain.
The milling process is designed to remove only
the outer bran layer and hull without breaking the
kernel.
It is often used in the U.S. as a carbohydrate
source for making beer because its bland flavor.
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Photo courtesy of
USDA
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Rice Milling
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Rice milling begins with whole grains of rice
being fed by machine between abrasive disks or
moving rubber belts. These machines, known as
shellers or hullers, do not crush the grains but
instead rub the outer layer of hull from the
underlying kernels.
The hulls are separated from the kernels by jets of
air and the kernels, known as brown rice, move to
another abrasive device called a rice-milling
machine.
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Rice Milling
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Here the inner layers of bran and germ are
dislodged by the rubbing action of a ribbed rotor.
The endosperms with bran and germ removed can
now be further polished to a white, high glossy
finish.
As in the case of wheat, the higher the degree of
milling or polishing, the lower are the remaining
vitamin and mineral contents. This is particularly
serious in the case of rice because entire
populations depend on rice as the principle item of
diet.
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Enrichment
Rice can be enriched in one of two ways;
1)Coat the polished rice with the enrichment
mixture (thiamin, niacin and iron) and then coat
the grains with a waterproof film material.
2)Parboiling whole rice including the hulls, bran and
germ in water for 10 hr at 70C. This causes the B
vitamins and minerals from the hulls, bran and
germ to leach into the endosperm. The rice is then
dried, milled and polished. This is often referred to
as “converted rice”.
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Corn
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Corn is consumed as both whole kernels ( a
vegetable) or as a flour.
Popcorn pops because the moisture expands upon
heating and explodes because it cannot escape.
Corn can be dry-milled like wheat or wet-milled.
Wet milling is popular and is used to make corn
syrups and high fructose corn syrup
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Corn
Corn is milled to remove hulls and germ,
both of which can be fed to livestock. The
germ is an important source of corn oil.
 Corn can be dry milled similar to wheat
where the end product is corn meal or if
further refined, corn flour. In this process,
the hulls and germ are also removed and the
endosperm reduced in size.
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Photo
courtesy of
the USDA28
Photo courtesy of USDA
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Photo courtesy of
USDA
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Wet Milling of Corn
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In wet milling, corn kernels are placed in large
tanks of warm water with generally an acid and
sulfur dioxide as a preservative.
The softened kernels are then run through an
attrition mill to break up the kernels. The pasty
mass is then pumped to settling troughs. Here is
where the oil rich germ floats to the top, is
skimmed off to be pressed for oil.
The watery slurry is then filtered to remove the
hulls.
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Wet Milling of Corn
The watery slurry now containing the starch
and protein fractions is passed through high
speed centrifuges to separate the heavier
starch from the lighter protein fraction.
 The starch is dried to yield “corn starch”.
 The protein fraction is dried and referred to
as corn gluten or zein which is commonly
used for animal feed.
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Corn Syrup
Corn syrup is made from the corn starch
fraction that has been exposed to acid or
starch-splitting enzymes.
 This hydrolyzed starch contains varying
proportions of dextrins, maltose and glucose
and is used as a sweetner.
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Barley, Oats and Rye
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Barley, oats and rye are primarily used for animal
feed.
Barley and rye also provide sources of
fermentable carbohydrate in the production of
fermentable beverages.
The flour from rye can be used to make flour for
breads but cannot be used by itself because the
protein content is too low.
Most oats used for human consumption are in the
form of rolled oats, an ingredient in breakfast
cereals.
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Barley, Oats and Rye
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Barley is also used to produce barley malt. In this
process, the barley seed is allowed to germinate to
a sprout. The dried barley sprout is now called
barley malt and is used in the brewing industry to
help digest starchy material into sugars for rapid
yeast fermentation. The malt also adds a
distinctive flavor to beer. Malt further adds flavor
to breakfast cereals and malted-milk concentrates.
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Breakfast Cereals
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Most breakfast cereals are made from the
endosperm of wheat, corn, rice and oats.
In “ready to eat” breakfast cereals, the endosperm
is broken down or ground into a mash and then
converted into flakes by squeezing the broken
grits or mash between rollers. The mash can be
extruded into a number of different shapes or the
endosperm can be kept intact as kernels to be
puffed as in the case of puffed rice.
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Breakfast Cereals
In all cases, the flaked, formed or puffed
cereals must be oven-cooked and dried to
develop the toasted flavor and to obtain the
crisp, brittle textures desired.
 This crispness requires that many ready-toeat cereals be dried to 3-5% moisture
content.
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Baking Science
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Baking Science
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Baking, by definition, refers to the
application of heat in an oven. This is a very
strict definition for baking. It can also
include all the reactions and processes that
occur before the item is placed in an oven.
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Classifications
Baked items can be placed in one of four
categories.
1)Yeast-raised goods –breads, etc leavened by CO2
from yeast fermentation
2)Chemically leavened goods-layered cakes,
doughnuts, biscuits etc that are raised by CO2 from
baking powders and chemical agents.
3)Air-Leavened goods- angel cakes and sponge
cakes made without baking powder
4)Partially leavened goods- pie crusts, certain
crackers, where intentional leavening agents are
used yet a slight leavening occurs from expanding
steam and other gases during the oven-baking
operation.
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Baking Ingredients and their
Function
The following goes through the major
baking ingredients and how they
function
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Gluten and Starch of Wheat Flour
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The principle protein in wheat flour is called
“gluten”.
Gluten has the property of when moistened and
worked by mechanical action, it forms an elastic
dough. This is accomplished by forming linkages
between protein molecules. The more the dough is
worked, the more linkages are formed. This is the
reason that doughs are “kneaded” when a strong
dough is required. However, the gluten can
weaken and breakdown under excessive
mechanical agitation such as over-mixing.
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Gluten and Starch of Wheat Flour
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Wheat starch does not form elastic films like
gluten but rather gelatinizes when moistened,
forming a paste material.
The character of the dough or batter depends on
the type of flour used. Real rigid doughs are made
from flours with a high gluten content (hard
wheat) and make good bread.
Flours with a lower gluten content (soft wheat)
make better batters that are less chewy and more
tender.
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Leavening Agents
Yeast and baking powders are not the only
leavening agents. Water in dough or batters
turns to steam in the oven and the
expanding steam contributes to leavening.
 Air in the dough or batter also expands
when heated and contributes to leavening.
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Yeasts
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There are two forms of yeast used in bakingmoist pressed cakes and dehydrated granules.
Both contain billions of living cells
(Saccharomyces cerevisiae) .
When rehydrated, both forms begin metabolism
and fermentation.
In fermentation, simple sugars are converted to
carbon dioxide gas and alcohol
The heat of the oven kills the yeast and inactivates
its enzymes thus stopping fermentation.
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Baking Powders
Baking powders contain particles of sodium
bicarbonate and some acid (like monocalcium
phosphate) and generate CO2 by the following
reaction;
3CaH4(PO4)2+ 8NaHCO3
Monosodium Phosphate + Sodium
bicarbonate
Equals
Ca3(PO4)2+4Na2HPO+8CO2+8H2O
Tricalcium phosphate+ Disodium phosphate+Carbon
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dioxide+ water
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Eggs
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Eggs can function as a principle structure builder
in cakes and also contribute to nutrition, flavor
and color of the finished product.
Like gluten, egg whites are a mixture of proteins
that forms films and entraps air when whipped and
on heating, it coagulates to produce rigidity.
The yolks of eggs contain similar proteins.
Eggs are important to use when working with lowprotein flours as in the case of angel cakes and
sponge cakes.
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Shortening
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Unlike flour and eggs, which are structure builders
and tougheners, shortening is a tenderizer. The
beating of shortening in some recipes is called for
to entrap air prior to the incorporation of other
ingredients to finish the batter. When the batter is
baked in the oven, the shortening melts and
releases the air bubbles which contribute to the
leavening action of baking powders and expanding
steam. The melted shortening then deposits around
the cell walls of the coagulating structure to
contribute a tenderizing effect and lubricate the
texture.
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Sugars
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Sugar, like shortening, is a tenderizer in
baked goods. It also adds sweetness and in
the form of sucrose, provides additional
fermentable substrate in yeast raised goods.
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Legumes and Oilseeds
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Legumes and Oilseeds
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Legumes are flowering plants having pods which
contain beans or peas.
Legumes include various peas and beans, most of
which are low in fat but soybeans are the
exception.
The term “oilseed” is applied to those seeds,
including soybeans, which are processed for their
oil.
Oilseeds include peanuts seed, cottonseed,
sunflower seed, rapeseed, flaxseed, linseed and
sesame seeds.
Both legumes and oilseeds contain considerably
more protein than cereal grains.
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Legumes and Oilseeds
Legumes (beans and peas) and oilseeds are
much higher in protein than grains and
oilseeds are much higher in fat than grains.
 Soybeans are legumes that have oilseed
characteristics.
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Soybeans
Soybeans are very versatile food products
used for both animal and human foods.
 Soybeans can have up to 23% fat.
 Soy protein is quite extensively used for
animal feed as a protein source.
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Photo courtesy of USDA
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Peanuts
Peanuts contain 25% protein and 50% oil.
They are used mainly to produce peanut
butter (50% of the crop).
 They can also be used to make flour and
used for oil.
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Photo courtesy of
USDA
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Conclusions
From this series, you should have learned;
1)The types, composition, structure and
processing of cereal grains
2)How breakfast cereals are made
3)The science of baking
4)The category of legumes and oilseeds.
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