Cereal Grains, Legumes and Oilseeds 1211

Cereal Grains, Legumes and Oilseeds1211 Steven C Seideman, PhD Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

Cereal Grains, Legumes and Oilseeds • 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.

Cereal Grains

Cereals • 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.

Photo courtesy of USDA

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.

Grain Corn Wheat Oats Rice Moisture Carbohydrates Protein Fat 11 72 10 4 11 69 13 2 13 58 10 5 11 65 8 2 Composition of Some Cereals Grains (%)

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.

Milling of Cereal Grains • 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”.

Cereal Grains • Typically cereal grains contain a moisture of 10-14% 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.

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.

Conventional Wheat Milling • 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.

Conventional Wheat Milling • 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.

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.

Uses of Wheat Flour • 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.

Rice • 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.

Rice Milling • 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.

Rice Milling • 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.

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”.

Corn • 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

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.

Photo courtesy of the USDA

Wet Milling of Corn • 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.

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.

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.

Barley, Oats and Rye • 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.

Barley, Oats and Rye • 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.

Breakfast Cereals • 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.

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-to-eat cereals be dried to 3-5% moisture content.

Baking Science

Baking Science • 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.

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.

Baking Ingredients and their Function The following goes through the major baking ingredients and how they function

Gluten and Starch of Wheat Flour • 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.

Gluten and Starch of Wheat Flour • 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.

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.

Yeasts • There are two forms of yeast used in baking- moist 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.

Cereal Grains, Legumes and Oilseeds 1211