Rice processing: Pearling

Rice bran, the outer layer of the rice grain, accounts for 8–10% of the total weight of the grain; however, it contains most of the nutrients: carbohydrates (34–62%), lipids (15–20%), protein (11–15%), crude fiber (7–11%) and ash (7–10%).

Pearling is increasingly recognized by the milling and baking industry as an important stage in cereal processing because it lowers the capital investment costs, giving as well, the benefit of better-quality products.

Pearling is a process in which a grain passes through a pearling machine. Pearling is done to lower the cooking times of grains and extend the shelf life. The pearling machines used an abrasive or friction process for bran removal.

The grains pass between the rolls and the bran is gently pearled off, leaving the pretty white kernels intact. The loose bran, which is stacked to the surface of the rice after the pearling process, is removed during a polishing step.

The removed bran is collected by aspirators, whereas the polished rice is graded since it contains different-sized broken rice pieces, bran, and dust. During grading the small broken rice pieces are separated by a vibrating sieve, whereas the remaining bran and dust particles are separated by air aspiration.

Pearling is the process, prior to milling removes effectively only the bran layers from the cereal grains, allowing nutritious parts, such as the aleurone layer to remain in the intact kernels.
Rice processing: Pearling

Milling in ancient Egypt

Neolithic Egyptians developed bread from emmer, barky, and even a type of millet. The grain was stored in beehive-shape silos until needed and they ground the grain on flat stones called querns and then baked in and oven or in heated clay bread molds.

Both men and women assisted in making bread, with men performing many of the tasks. Women generally were the millers. Figures of women milling grain have been found in the tombs of the later Old Kingdom (c.2575-2510 BC) to early Middle Kingdom (c.2030-1640 BC).

Milling itself was a tedious process and the cause of many injuries. Several handfuls were place on a stone quern with a gently curve surface for milling. The upper surface is not perfectly smooth, but is kept somewhat roughed. A stone shaped like rolling pin with a curve to match the curvature of the grinding surface was rolled back and forth, grinding the grain into flour, which was caught in a container at one end of the quern.

The miller kneeled over on the ground, grinding on the wide saddle quern; then in the Middle Kingdom, the milling process was performed on workbenches. The rotary quern was not invented until about the fifth to third centuries BC, somewhere in the western Mediterranean.
Milling in ancient Egypt

Grain stored pest predators

Use of predators is one of many conventional biological techniques for stored –grain pest control. Others are including, use of parasites, insect disease and sterile males, the use of pheromones for pest monitoring, mating disruption or enhanced mass trapping, and the use for resistant crop varieties.

Many storage pests will prey on other insects present including members of their own species. Obligate predators only feed on other insects.

Lyctocoris campestris is a worldwide generalist predator of stored product insects that produces best growth and reproductive responses when exposes to grain moths instead of to common stored product infesting beetles.

Xylocoris flavipes, a cosmopolitan species called the warehouse pirate bug, is commonly found associated with stored product insect pests and studies showed they inhibited population buildup of four species of beetles that attack stored grain.

Some interesting biological characteristics of the warehouse pirate bug are that it requires a low number of prey to complete its development and uses cannibalism to survive when prey are absent.
Grain stored pest predators

Quick cooking rice

Pregelatinized and packaged rice without excess drying has been developed in Japan. This type of rice is popular because of their short cooking time, instant and quick-cooking rice are partially or fully cooked before they are packaged.

This form of rice is widely available and only takes a few minutes to prepare by rehydrating and heating; it is widely used for its conveniences.  Consumers only have to add the tasty cooking soup or water and cook for about 15 minutes. Cooking time of both brown and white rice is shortened by heating the dry grains in a current of air at elevated temperatures.

The kernels are so modified by fissuring of the surface layers, by dextrinization, and in the case of brown rice, by loosening of the bran layers, that the cooking time in the home is reduced to about one-third that of raw rice.

Compare with instant rice; quick cooking rice is improved in terms of taste and texture. After cooking, the product should match the characteristics favor, taste and texture of conventionally cooked rice.

The product should be packaged properly in plastic film bags of special design against moisture changes during storage.
Quick cooking rice

Amaranth grain

Amaranth a little known crop of the Americas, it’s grown either as a grain crop or as a leafy vegetable. Amaranth grain is very small (about half the size of millet), and may be light yellow, brown-yellow or brown-black in color.

Amaranth grain species are ‘pseudocereals’. Well-known Amaranth grain includes A. cruentus, A. hypochonriacus and A. caudatus.  This species is a crop in the Andean highlands of Argentina, Peru and Bolivia.

Amaranth grain makes a tasty porridge and can be toasted to make crunchy topping. The flour must be mixed with other flour for baking.

Amaranth grain has a high protein as well as a high-fat content and can supply an excellent balance of carbohydrates, fats and proteins. Amaranth has a protein content as high as 16%, which is somewhat higher than that found among commercial varieties of common cereals.

The grain is easy to digest and customarily given to those who are recovering from an illness or a fasting period.

Amaranth is high yield potential. It typically gives a grain yield of 2,250 – 4,500 kg/ha and fresh weight of leaf and stem of 30,000 – 60,000 kg/ha.
Amaranth grain

What is breakfast cereal?

Breakfast cereals have been define as “processed grains for human consumption”.

Indeed, one or more of the cereal grains or milled fractions thereof indeed major constituents of all breakfast cereals, approaching 100% in the case of cereals for cooking.

The portions drops well below this in many ready to eat cereals, and less than 50% in presweetened products having nutritive sweeteners )sucrose, or fructose, dextrose, and other corn-based products) as substantial constituents.

In broad terms , then, breakfast cereal ingredients may be classified as:
1) grains or grain products,
2) sweeteners, caloric or otherwise
3) other flavoring or texturizing macro ingredients
4) microingredients for flavor or color, micro ingredients for nutritional fortification and shelf life preservation.
What is breakfast cereal?

Cleaning of the grain

Cleaning is accomplished by:
*Screening out the larger particles with the chaffer and sieves
*Blowing out the lighter particles with a fan blast, or
*Screening out the smaller particles in a recleaner

The impact of grain breakage and fine materials on all aspects of the system has resulted in the need to clean grain.

The modern combine harvester produces remarkably clean grain compared with the manual and partially mechanized processes.

Cleaning decreases the airflow resistance, increases airflow, and increases the cooling rate of the grain if aeration is used.

For good storage the chaff, dust and straw must be removed. Broken and foreign grains should not be present: the former encourage insect attack, the latter lower market value.

Broken grains, grain dust and other fine grains have the greatest effect in the performance of insect control interventions.

A typical grain cleaner, often called a scalperator or scalping machine, consist of two parts, a shaking screen and a fan, driven from the same more. Straw and other large objects are removed by screening and the dust and other lightweight material are blown out by aspiration.

The amount of grain cleaning required prior to storage involves the factors of risk to grain deterioration as a result of mold and insect invasions and the costs associated with maintaining quality.

Cleaning of the grain

Grain physical properties important to storage and transport

The cereals are traded internationally as whole grains or as final rather than intermediate products. These include pasta foods and high value products containing cereals.

Therefore it is important the physical properties of cereals in order to predict grain pressure packing behavior and flow behavior include bulk density of the grain, the ratio of lateral to vertical pressure, the internal angle of friction and the coefficient of friction of grain on the bin wall.

For successful storage it is important to avoid excessive temperature, high moisture, predation by insects and other invertebrates. The important points of cereals properties for storage include:
*The soft floury endosperm. This favored by weevils as being a more easily eaten food that the vitreous endosperm. Hard vitreous grains are more denser and more difficult for insect to penetrate.

*The embryo. If this has been damaged at threshing or during handling, the inherent enzymes will break down the fat, leading to off-flavors in foods made from the grains.

*Size and shape of the grains. Small grains less than around 12 g per 1000 grains are not attacked by weevils.

Insect infestation deteriorated grain quality, Nutritional value in terms of thiamin content decreased in infested wheat together with changes in physiochemical properties including weight, density, increased uric acid and fat acidity increased moisture content and changes in crude fat, calorific value, true proteins, ash, crude proteins, crude fiber and non- protein.

The physical properties vary in the same way as the composition. In addition, harvesting, handling, storage and abuses during movement of grain from storage cause significant changes.

Storage can be for varying lengths of time, ranging from short term storage on farm for drying and waiting for advantages market iodations to long term storage for strategic reserves.

Grain ages during storage and changes it properties significantly, which means that processing properties change.
Grain physical properties important to storage and transport

Square Necked Grain Beetle

Square Necked Grain Beetle
Cathartus quadricollins. Adults are about 2 mm long, and the oval body is shiny, reddish brown, and somewhat flattened.

This grain beetle is native to American continent, is noted as a pest of corn both in field and silo.

This species is similar in appearance to the sawthoothed grain beetle, Oryzaephilus surinamenis, but lacks the six projections on the lateral margins.

Cathartus quadricollins often common in United States. It is also common in the humid parts of West Africa.

This beetle is chiefly abundant in the South of United States, where it is found in great numbers outdoors infecting the seed pods of a great variety of plants.

The larvae have a bad habit of devouring the germ of the seed in which they breed.

Laval development at 80% RH is 24-26 days at 25 degree C and 20 days or less at 30 degree C.

This species is cosmopolitan and has been found in wheat, rolled barley, rice, dried fruits, cocoa, tobacco, and oil palms.
Square Necked Grain Beetle

Grain Weevils

Grain weevils are in the family Curculionidae and contain three highly changing pest species: Sitophilous oryzae (L.) rice weevils, S. granaries (L.) granary weevils and S. zeamais Motschulsky (maize weevils).

Adults are 0.3-0.6 cm in length and have an elongated snout containing the mouth parts that are typical of all weevils.

Grain weevils have a worldwide distribution but none thrive in tropical and subtropical regions.

They attack primarily whole grain and seeds and typically do not reproduce on fine products such as flour, but can infest formed cereal products such as pasta.

Female deposits eggs singly in holes excavated into seeds and then cover the eggs with a mucilaginous egg plug.

Adults live a long time and females can lay a large number of eggs over their lifetime.

Larvae develop and pupate within the seed and after eclosion adults chew out of the seed. Because larvae pupae and adults can occur inside whole kernels, these species can be more difficult to detect and this contribute to fragment counts in processed grain products.
Grain Weevils

Wheat Structure

Wheat Structure
Wheat structure is a single seeded fruit, 4 to 10 mm long, consisting of a germ and endosperm enclosed by an epidermis and a seed coat.

The fruit coat or pericaprs (45 to 50 um thick) surrounds the seed and adhere closely to the seed coat.

The wheat color, depending on the species and other factors is red a to white and is due to material present in the seed coat.

Wheat also is classified based on physical characterizes such as red, white soft, hard spring or winter.

The outer pericaprs is consist of the epidermis and hypodermis. The epidermis consists of a single layer of cells that from the outer surface of the kernel.

On the outer walls of the epidermal cells is the water impervious cuticle. Some epidermal cells at the apex of the kernel are modified to form hairs.

The hypodermis is composed of one to two layers of cells. The inner pericaprs is composed of intermediate cells and cross –cells inward from hypodermis.

Long and cylindrical tube cells constitute the inner epidermis of the pericaprs. In the crease, the seed coat joins the pigment strand, and together they form a complete coat about the endosperm and germ.

Three layers can be distinguished in the seed coat: a thick outer cuticle, a “color layer” that contains pigment, and a very thin inner cuticle.

The bran comprises all outer structures of the kernel inward to, and including the aleurone layer.

This layer is the outer layer of the endosperm, but is considered as part of the bran by millers.

The aleurone layer is usually one cell thick and almost completely surrounds the kernel over the starchy endosperm and germ.

The endosperm is composed of peripheral, prismatic and central cells that are different in shape, size and position within the kernel.

The endosperm cells are packed with starch granules, which lie embedded in a matrix that is largely protein.
Wheat Structure

Cereal in general

Cereal in general
Cereals are monocotyledonous plants that belong to the grass family. Based on botanists’ approximation, there are about 350,000 plant species, of which about 195,000 species are economically important flowering plants.

Nearly 50 species are cultivated worldwide and as few as 17 species provide 90% of human food supply and occupy about 75% of the total tilled land on earth.

They consist of wheat, rice, corn, potato, barley, sweet potato, cassava, soybean, oat, sorghum, millet, rye, peanut, field bean, pea, banana and coconut.

The cereal grains such as wheat, rice, corn, barley, oat, rye, sorghum and millet provide 50% of the food energy and 50% of the protein consumed on earth.

Wheat, rice and corn together make up three-fourths of the world’s grain production.

In general, cereal grain have been considered as the source of carbohydrates to supply food energy to the diet. Cereal grains, especially rice and wheat, provide the bulk of energy consumed on earth.

The cereal crops that are grown for their edible fruit are generally called grain, but botanically referred to as caryopsis. The cereal seed consist of two major components, the endosperm and embryo or germ.

The endosperm encompass the bulk of the seed and is the energy source of stored food.

An outer wall called the pericarp that develops from the ovary wall encases the endosperm. A semi-permeable layer under the epicarp, which is called testa, surrounds the embryo and is derived from the inner ovary wall.

The testa is permeable to water but not to dissolved salts an is important for germination. The third layer, which is called aleurone, contains thick walled cells that are free of starch. The pericarp, testa and aleurone layer are collectively called the bran.
Cereal in general

Composition of Cereal Grains

Composition of Cereal Grains
In composition, grains are structurally similar as seen; however, they vary in their nutrient composition, containing varying amounts of carbohydrate, fat, protein, water, vitamins and minerals.

The main nutrient component of cereal grains is carbohydrate which makes up 79-83% of the dry matter of grain.

It exists predominantly as starch, with fiber especially cellulose and hemicellulose, composing approximately 6% of the grain.

Lipid (fats and oil) makes up approximately 1-7% of a kernel, depending on the grain. For example, wheat rice, corn, rye and barley contain 1-2% lipid, oats contain 4-7%. The lipid is 72-85% unsaturated fatty acids, primarily, oleic acid and linoleic acid.

Protein composes 7-14% of the grain, depending on the grain. Cereals are low in the amino acids tryptophan and methionine, and although potential breeding may produce cereals higher in the amino acid lysine, it remains the limiting amino acid in cereals.

Grain consumption provides half of the protein consumed worldwide. However, in comparison to foods such as milk, meats or eggs, grains do not include all the essential amino acid contained in animal protein.

The protein is of low biological value and therefore, less efficient in supporting body needs.

Combining food sources of protein is common in cultures throughout the world.

The preparation of traditional dishes combines the lower biological value grains with legumes or nuts and seeds to provide the needed amino acids to yield a complete dietary protein.

For example a combination of beans with rice, or beans with cornbread, tofu and vegetables, or tofu and cashews, chickpeas and sesame seed paste (tahini) known as hummus, peanut butter on whole wheat bread and so forth are combinations creating complete proteins.

Vitamins present in cereals are predominantly the B vitamins-thiamin (B1), riboflavin (B2) and niacin (B3). These vitamins may be lost in the milling process and so are added back through the process of enrichment.

Whole grain products contain some fat soluble vitamins in the germ.

Water is present in cereal grains at levels of 10-14% of the grain. Of course soaking and cooking add water to cereal grains, and the grain size expands as additional water is absorbed.

If flour is high in protein content, it absorbs a lot of water compared to low protein flour.

Mineral are naturally present at higher levels in whole grains than in refined grains. Fortification of refined flour with added iron is common.

Zinc, calcium as well as vitamins also may be added at levels beyond not present in the original grain.

Fiber content is determined by different analysis and includes crude fiber (CF) and total dietary fiber (TDF).

These two measurements are not correlated. Crude fiber is composed of cellulose and the non-carbohydrate lignin. TDF includes cellulose and lignin, plus hemicellulose, pectic substances, gums and mucilages.
Composition of Cereal Grains

Sorghum

Sorghum
The genus of Sorghum is found in warm, dry climates, especially in Africa, India, Pakistan, China and the Southern USA where its members are grown as important grain or forage crops. Because sorghums have been in cultivation for a long time and because interspecific hybrids are easily formed, the taxonomy of the genus is somewhat confused.

Until recently the cultivated types were loosely grouped together in the species Sorghum vulgare, but a thorough revision of taxonomic relationships suggests that Sorghum bicolor is the species to which the grain crops should belong.

The seed of grain sorghum or dura as it is often called, contains no gluten, and hence is by itself not suitable for bread making. Normally for human consumption the grain is group into flour, mixed with water or fat and cooked to form a porridge or batter.

Alternatively, the grain is fed to pigs or poultry, its starch may be used for a variety of purposes such as an adhesive or for sizing or it may be fermented to produce alcohol. Sorghum are also grown as forage crops and may produce high yields of the order of 30,000 kg/ha from several cuts throughout the year.

Best resulted are obtained from special forage types such as sorgo, sweet or sugar sorghum which is variously described as a variety of sorghum or as a separate species (Sorghum saccharatum). Sudan grass (S. Sudanese), a tall and tufted tropical grass, is often used top produce hybrids with sorghum, as for example the production forage plants Sudax or Sordan.

One possible problem with these forages is that contained in the leaves there may be a cyanogenic glycoside, dhurrin, which when eaten by animals hydrolyses to form poisonous hydrogen cyanide.

In ruminants, hydrogen cyanide is rapidly detoxified in the rumen and liver by reaction with sulphide or cystine, but the danger of toxicity remains of glycoside levels are high or sulphur intake is low. The problem can be avoided by the choice of safe cultivars by not allowing stock to graze very immature growth, or by feeding as hay or silage.
Sorghum

Grain Processing: Milling

Grain Processing: Milling
Threshing removes the grain from the stem. However, the grain is not usually ready for cooking until the husk (glumes) has been removed.

Wheat, sorghum and pearl millet usually thresh naked that is without the glumes. Maize is on a cob covered with a sheath: the sheath must be removed and the grain taken from the cob.

A combine harvester threshes the maize free from both sheath and cob. Barley, oats, rice and most of the small millets thresh with the glumes adhering tightly to the kernel so that even a modern threshing machine or a combine harvester cannot remove the grain from this husk.

The first step in any milling process for this latter group is to remove the glummer.

This is done by rubbing the grains one against the other in a mortar or by simple rotary machine, by splitting off the glumes in a disk huller, or by use of rubber rollers rotating at a differential speed. The objective at this stage of milling is to obtain as high an out-turn as possible of whole grains.

Once free from glumes, all grains may be treated in the same way. Cereals have an outer layer and a gem, known collectively as bran, which is rich in lipids that rapidly oxidize to give off-flavors.

The bran also tends to be less easily digested than the endosperm.

The objective of the second stage of milling is, therefore, to remove the bran. In the case of rice, the grain is required whole, so great care is taken not to break the grain.

Most other cereals are eaten as flour or meal (a coarse flour). The more of the bran that is removed, the better the flour will keep.
Grain Processing: Milling

Wheat Grain Processing

Wheat Grain Processing
Wheat is harvested by combines that cut the stalk remove and collect the seed, and either return the straw to the soil, to be plowed under with the stubble and thus provide hummus or compress and bale it for future use as litter, ensilage and so on.

Wheat may be bagged in jute sack and stored in warehouses or it may be stored in bulk in elevators. The latter method provides the best protection against rodent and insect infestation.

The moisture content of bulk stored wheat should not be higher than 14.5% and that of sack stored wheat not higher than 16%. Otherwise, microorganism may grow and cause heating and spoilage. When it is necessary to lower the moisture content of wheat it may be dried in bins by blowing hot air (not higher in temperature than 175 degree F) across the bins.

In preparing wheat for milling, it is blown into hopper scales that record the quantity of uncleaned wheat. Some of the coarser impurities are removed by this process. The grain then passes over a series of coarse and fine sleeves that further remove contaminating materials, including chaff and straw. Still in dry states stones may be removed by passing wheat over short openings that allow the heavier stones to fall out of mass and be trapped.

The wheat is next passed over discs or cylinders containing indented surface that remove seeds short or longer than wheat following a pass through a magnetic separator to remove any metals present. The next cleaning process is dry scouring to remove adhering dirt.

The wheat is then washed in water, a process that both removes dirt and adds 2 – 3% water to the grain. The added water is necessary to provide desirable conditions for milling. A stone trap is including in the washer. Excess water is removed by centrifugation. A second wet cleaning with a light brushing action is ordinarily used, followed by aspiration (blowing air through the grain), which is the final cleaning operation.

The grain is then carried into a bin from which it is fed to the milling operation. This bin is located on the top floor of the flour mill, the grain having been elevate do this position during the various cleaning operation.

In milling, grain is fed automatically though scale hoppers that regulate the flow of the seeds at rates corresponding to those of the following operations:

Milling may be carried out by passing the grain through a series of corrugated rolls rotating toward each other, which remove chunks of the endosperm from the bran. After each passage through the break rolls, the material is sifted through cloth, or wire sieve and separated according to particle size.

The various streams of different sized flour particles are finally blended to provide the different grades of flour. The more finely ground flour is nearer to white but less nutritious than the coarser ground flour.

This results from the more effective removal of bran and germ from finely ground flour. Impact milling is now used in some operations. With this method, the seed is broken open by impact in a machine. Flour particles of different sizes are separated by air classification or by centrifugation.
Wheat Grain Processing

Cereal Nutrition

Cereal Nutrition
Long before people learned to cultivate the grasses that are today’s cereal grain, they relied upon such grains as a source of nutrients.

It is thus only natural that breakfast cereals made from the cereal grains through modern processing techniques have become primarily contributors of nutrients to our diets.

The nutrients provided by this first meal of the day include those that are indigenous to the cereal grains as well as some that are added in the manufacture of the cereal.

The nutrient contribution of cereal applies to all age groups. Processed cereals are usually the first solid food fed to infants and the cereal feeding frequently is the first of the day.

No one can doubts on the popularity of breakfast cereals among children; all one has to do is look on store shelves at the large number of breakfast cereals designed to appeal to children.

According to one study, among children aged 5-12, those who ate ready to eat cereal three or more times a week consumed significantly less fat and cholesterol and more fiber, B-vitamins and vitamins A and D than those who ate no ready to eat cereal at breakfast.

Cereal made contributions to adult as well. One study shows that breakfast consumption patterns of adult aged 50 and over and concluded that for all age and sex classes, consumption of ready to eat cereal at breakfast increased the average daily intake of all vitamins and minerals particularly those identified as under consumed by elderly individuals.
Cereal Nutrition