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Study Guide - Module 4
Food Technology (FDS308)
Charles Sturt University
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FDS
Food Technology
FACULTY OF SCIENCE
Module 4 201830
FDS308
Food Technology
FDS308 Module 4 Technology of cereals
Faculty of Science
Originally written and compiled for FDS301 by Dr. Jian Zhao
Adapted for FDS308 by Dr Ester Khosa
iii
Contents
- Module profile Page
- Topic 1 Cereal crops - production and uses
- Introduction
- Cereal production world wide
- Topic 2 Structure and chemical composition of cereal grains
- Introduction
- Chemical composition of cereal grains
- Topic 3 Wheat flour milling
- Introduction
- Objectives of flour milling
- Cleaning of wheat
- Conditioning (tempering) of wheat
- Milling of wheat
- Milling by-products
- Extraction of gluten from wheat flour
- Topic 4 Properties, quality and uses of wheat flour
- Introduction
- Wheat quality and grading
- Flour improvement
- Fine grading of flour
- Flour for special purposes
- Flour quality and testing
- Topic 5 Technology of bread making
- Introduction
- Biochemical and rheological changes during bread making
- Bread making processes
- Frozen dough production
- Bread staling
- Microbial spoilage of bread and prevention
- Topic 6 Technology of biscuits
- Introduction
- Ingredients of biscuits
- Biscuit manufacturing processes
- Secondary processing of biscuits
- Packaging of biscuits
- Topic 7 Processing of oats, maize and rice iv
- Introduction
- Maize milling
- Products of wet-milled maize, their uses and further processing
- Rice milling
- Topic 8 Breakfast cereals
- Introduction
- Hot-serve breakfast cereals
- Ready-to-eat breakfast cereals
- Keeping quality of breakfast cereals
reinforce the concepts covered in the notes, and to provide some additional information on relevant topics. Information that is in the reading material but not covered in the notes will not be examined.
Assessment: See Subject Outline for assessment details.
Topic 1 Cereal crops - production and uses
Objectives
Upon successful completion of this topic, students should be able to:
appreciate the importance of cereals as human food; and
identify the eight major cereals cultivated in the world and those cultivated in Australia.
Introduction
Cereals are the fruits of any cultivated grasses. The principal cereal crops used for human or animal food are wheat, rice, barley, oats, maize (corn), rye, sorghum and millet.
Cereals are staple foods in many parts of the world. The cultivation, production and use of cereals have always been an important part of human activities and the success of these activities has played a fundamental role in the development of civilisation. Today, with the rapid growth in the world’s population, the stability and general well being of human society may well be determined by whether we can provide sufficient food for mankind. That, in turn, is largely dependent on how well we can manage the production and use of cereal crops.
Cereal production world wide
In 1999, about 5% of the entire land surface of the world was occupied by cereal crops. Although there are yearly fluctuations, the world total production of wheat, rice, barley, oats, maize, rye, sorghum and millet has shown a trend of steady increase over the last three decades. The world produced about 1870 million tonnes of the eight major cereals in 1999, an increase of more than 50% over the production in 1960. Over the same period, the land for cereal crops increased only slightly. The increase in cereal production is due to increases in crop yield, resulting from better irrigation, introduction of high yield and disease resistant crops, better farm management, and reduced harvest loss.
The total world production of cereals would be able to provide approximately 350 kg of grain per head per annum, if it was distributed equally among the entire world population.
Wheat, rice and maize are the predominant cereals cultivated worldwide, representing about 29%, 27% and 25% of the total cereal production in the world, respectively. Table 1-1 shows the percentage distribution of world cereal production and the average yield for each cereal over the period 1987-1989.
Due to our small population, about 80% of wheat produced in Australia is exported. This represents about 12% of the world wheat trade. Other major wheat exporters are the EU countries (33%), USA (28%), Canada (18%), and Argentina (6%). Major wheat importers are the former USSR states (15%), China (13%), Japan (6%), the Middle East, India, Pakistan, and Korea. About 66% of the world wheat production is used for human food, 20% for feed, 7% for industrial uses, and 7% for seed.
Wheat for human consumption must meet certain quality requirements. A wheat grain passes through many hands from grower to consumer, all of whom have different requirements for quality. For example, growers are mainly concerned with yield; millers require wheat of good milling quality; bakers want flours suitable for making different products such as bread, cakes and biscuits; and the consumer want the food made from wheat to be safe, nutritious, and of good appearance, texture and flavour. These quality requirements for wheat at different stages of processing will be discussed in detail in this module.
Most of the wheat produced is milled to produce flour, which is used for making products such as bread, biscuits and cakes. A small amount of wheat is processed to make breakfast cereals such as porridge and flakes. Technologies for making these products form core parts of this module.
Rice
Rice is grown in tropical and temperate regions where rain and sunshine are abundant. Rice is a typical cereal of the swamp, but it can also be grown on dry land or under water. Rice, like wheat, is a major staple in many parts of the world, particularly in Asia where two crops may be grown per year. China is the largest producer of rice in the world. Other major producers are India, Indonesia, Bangladesh, Thailand, Vietnam, Burma, Korea, Japan and Brazil. Thailand is the largest rice exporter in the world, followed by the US, Vietnam and Pakistan. Italy, Spain, China, India, Iraq are the major rice importing countries.
In comparison, Australia is a minor rice producer. Annual production is over one million tonnes. About 95% of Australian rice is produced in the Murrumbidgee irrigation area of NSW and the remainder in northern Queensland. Australian rice is primarily the long and medium grain types. Japonica is the most widely planted variety. Australian rice growers are the most efficient in the world and hold the world record for rice yield.
Rice is mainly used for human consumption. Only a small percentage is used for industrial purposes and for seed. Rice is mainly consumed as whole grain after the husk and bran are removed by milling.
Maize (corn)
Maize is cultivated in regions that have at least 90 days of frost-free conditions. The crop needs temperatures of 10-45°C and grows best between the latitudes of 30 ° and 47°. The USA is the largest producer of maize, accounting for 43% of the world total production, followed by China (18%), Brazil (5%), Europe (5%),
Mexico (3%) and South Africa (2%). The USA is also the world’s largest exporter of maize. Other major maize exporters are China, Argentina and South Africa. The major maize importing countries are the former USSR states, Japan, Western Europe, Korea and Taiwan. Maize is not a major crop in Australia. Only about 250,000 tonnes of maize is produced annually.
About 64% of world production of maize is used for feed, 21% for human consumption, 14% for industrial uses and the remainder for seed. Maize for human food is mainly consumed in various kinds of breakfast cereals such as corn flakes and corn grits. A smaller amount of corn flour is used as ingredients for various bakery products. A large proportion of corn is wet-milled for producing starch. Some of the corn starch is used directly as food ingredients such as thickeners, but most of it is further processed to make various types of corn syrups, which is used in a wide range of products, especially soft drinks. Technologies of making these products (breakfast cereals, corn starch and corn syrups) are important components of this module.
Oats
Oat crops are widely grown in temperate regions. They are more successful than wheat and barley in wet climates, but do not stand cold well. The principal oat producing countries are the former USSR, the USA, Canada, Poland, Australia and Germany. The bulk of oat production is utilised domestically, only about 4% enters world commerce. Argentina, USA, Canada and Australia are the major oat exporters, while Europe is the main importing region. Oats is the third largest crop grown in Australia after wheat and barley, with about 1 million tonnes produced annually. It is grown mainly in southern NSW, Victoria, South Australia and Western Australia. About 80% of oats produced is consumed on the farm as stockfeed, 7% for human consumption and 12% for seed.
Oats for human consumption are sold mainly in the form of breakfast cereals such as oatmeal porridge, rolled oats and instant oats. The technology for making these products are described later in this module.
Barley
Barley is cultivated in temperate climates mainly as a spring crop. The distribution of barley growing areas in the world is similar to that of wheat. Barley grows well on well-drained land and the soil requirement is less than that of wheat. The major barley producing regions are the EU countries, the former USSR states, Canada, the USA, and Eastern Europe. The major barley exporting countries are France, Canada, UK, and the USA. The major barley importers are the former USSR states, Japan, the Middle East and China.
The principal uses of barley are as stockfeed in the form of barley meals, for malting and brewing in the production of beer, and for distilling in the manufacture of whisky. Barley meals are sometimes used as ingredients for bakery products and breakfast cereals.
Topic 2 Structure and chemical composition of cereal grains
cereal grains
Objectives
Upon successful completion of this topic, students should be able to:
describe the general structure of cereal grains;
list the main components of cereals;
describe the chemical structure of and the differences between amylose and amylopectin;
describe the properties of starch granules, especially gelatinisation and retrogradation;
list the major components of cereal proteins and their solubility; and
describe the composition of gluten.
Introduction
The basic anatomical structure of all cereal grains is quite similar although there are certain differences in detail. Cereal grains are in botanical terms fruits, known as caryposes, although they are commonly referred to as seeds. The grain of wheat, maize, rye and sorghum contains a seed enclosed in a fruit coat called the pericarp; the seed itself is composed of a seed coat, the embryo (germ) and endosperm. Grains of rice, oats and barley have additional fused glumes outside the fruit coat, commonly known as the hull or husk. Biologically, the husk functions as a protective barrier, protecting the seed from physical damage, microbial activity and insect attack. Thus, a grain kernel (excluding the hull) comprises four main parts: pericarp (fruit coat), testa (seed coat), germ and endosperm. A ‘generalised grain’ structure is given in Figure 2. Each of these parts are divided into various layers, tissues or regions, as listed on the left-hand side of Figure 2.
Kernel (caryopsis) 1. Pericarp (fruit coat) (a) Outer Epidermis (epicarp) Hypoderm Remnants of thin-walled cells (b) Inner Intermediate cells Cross cells Tube cells 2. Seed (a) Seed coat (testa) and pigment strand (b) Nucellar layer (hyaline layer) (c) Endosperm Aleurone layer Starch endosperm (d) Germ (embryo) Scutellum (cotyledon) Embryonic axis Plumule, covered by coleoptile Primary root, covered by coleorhiza Secondary lateral roots Epiblast
Beeswing
Bran
(a) (b)
Figure 2: Generalised cereal grain and its anatomical structure components.
a. Source: Kent, N. L. (1975). Technology of cereals with special reference to wheat (2nd ed., p. 29). Oxford: Pergamon.
b. Source: Kent, N. L., & Evers, A. D. (1994). Technology of cereals (4th ed., p. 36). Oxford: Pergamon.
Note: Students are advised to study the grain structure so that they can understand milling processes (described in later topics) better, but not required to memorise the detailed structure and the botanical names.
Wheat
Wheat grains are ovoid in shape and round at both ends. The pericarp of wheat has a layered structure and serves as a protective coat for the seed within. In ripe wheat grains, the pericarp appears thin and papery. The outer layer is frequently peeled off during cleaning, conditioning or milling, and is known as beeswing. The seed coat (testa) of wheat grain is a thin single or double-layered structure. In some varieties of wheat, the inner layer is pigmented and gives the grain its characteristic colour (e. certain varieties of wheat are red or pink coloured).
The pericarp and the aleurone constitute the bran. The bran layer is rich in protein, fibre and minerals. The endosperm is composed of tightly packed starch granules embedded in a protein matrix. The starch and protein of the endosperm function as a storage of nutrients of the seed, which are used during germination. The embryo (germ) is rich in proteins, lipids and B group vitamins.
The physical structure of the oat kernel (groat) is rather similar to that of wheat and barley.
Maize
The grain of maize (corn) is the largest of all the cereals. The kernel is wedge- shaped, broader at the apex end than at the end attached to the corn cob. The maize grain consists of five principal parts: the hull, tip cap, pericarp, endosperm and germ. The hull is composed of the pericarp fused with testa, equivalent to the bran of other cereals, but different from the ‘true’ hull (husk) of rice, barley and oats, which is formed from the lemma and palea. The tip cap is that portion of the hull lying over the germ. The germ of maize is much larger than other cereals, accounting for 10-14% of the kernel weight. It is rich in lipids, which are commercially extracted for oil.
Sorghum, rye and millet
The grain of sorghum is round and small, varying in weight from 8 to 50 mg according to cultivars. It consists of the germ and endosperm enclosed in a seed coat (testa), and the pericarp (fruit coat). In many varieties the testa and the pericarp are fused into one integrate protective cover.
The grain of rye is similar in physical structure to that of wheat, but is slightly smaller and slender.
The kernel of millet (also called pearl millet) has a shape resembling a tear drop and is about a third the size of the sorghum kernel, with an average weight of about 9 mg. The size of the grain varies considerably according to varieties, so does its colour, which ranges from near white to yellow, brown, blue and purple. The structure of the millet kernel consists of the germ and the endosperm enclosed in the pericarp; the testa (seed coat) is virtually absent. The kernel contains a relatively large germ (about 17% of the kernel weight), which, being rich in lipids, makes the grain or flour susceptible to biological and chemical spoilage during storage.
Chemical composition of cereal grains
The mature grain of cereals consists of carbohydrates, nitrogenous compounds (mostly proteins), lipids, water, minerals, and small amounts of vitamins, pigments and other substances.
Quantitatively, carbohydrates are the most abundant component of cereals. On a dry matter basis, they constitute about 83% of wheat, barley, maize, sorghum, rye, rice and millet, and about 79% of oats. The second most abundant constituent is protein, which forms 9-16% of the dry matter of cereals. In general, wheat has a higher content of protein while the protein content of rice is the lowest among the cereals mentioned. The next major component is lipids, which vary greatly in concentration among the different cereals. At the lower end, polished rice contains only about 0% lipids; while at the upper end, some varieties of maize contain as
much as 9% lipids. The mineral content of cereal is generally below 3% with the exception of paddy rice (with the husk on), which contains about 7% minerals on a dry matter basis. Minerals of rice are mostly contained within the husk. The mineral content of brown rice (husk removed from the grain) is only about 2%.
Carbohydrates
Carbohydrates in cereals can be divided into two parts: the crude fibre and soluble carbohydrates. Crude fibre is that portion of the carbohydrates that is insoluble in dilute acids and alkalies under prescribed analytical conditions. The soluble carbohydrates are calculated as the total dry matter of the grain less crude fibre, nitrogenous substances, lipids and minerals. Although this division is an analytical one, the two classes of carbohydrates are different in chemical composition, digestibility and nutritional values. Soluble carbohydrates consist of starch and sugars, are digestible by the body and serve as a source of energy. Crude fibre includes cellulose, hemicellulose and pentosans, and are generally not digested by the human body. Most of the crude fibre is also dietary fibre.
Starch
Starch is the most abundant and important carbohydrate in all cereals. It accounts for about 64% of wheat grain on a dry matter basis, and about 70% of the wheat endosperm.
There are two types of starch in cereal grains, known as amylose and amylopectin. Both are polysaccharides composed of the same monosaccharide unit - glucose. The difference is in the structural arrangement of the glucose units. Amylose is essentially a linear polymer in which glucose residues are linked by α-(1→4) bonds; while amylopectin has a highly branched structure in which α-(1→4) linked glucose segments containing 20-40 glucose residues joined together by α- (1→6) branching points. Another difference between these two polymers is their molecular size. While amylose may contain up to 5,000 glucose units, amylopectin is much large, containing up to 10 6 glucose residues.
In solution, amylose molecules adopt a helical structure with 6 glucose residues in each turn. When an iodine reagent is added to the solution, the iodine ions are incorporated in the core of the helix, which produces a characteristic deep blue colouration. Other molecules such as organic acids, alcohol and lipids can also be incorporated in amylose in a similar manner. Amylopectin, due to its branched structure, cannot form a helix and does not produce the deep blue colouration. It stains brownish red.
The ratio of amylose to amylopectin in starches varies with the genotype of the cereal. Starch from common cereals such as wheat contains about 25-27% of amylose. In some of the high-amylose varieties of barley and maize, amylose content can be as high as 40%. Starches from rice, sorghum and low-amylose maize and barley, on the other hand, are composed almost entirely of amylopectin and, due to the fact that amylopectin has a higher peak viscosity (see later sections), these varieties are commonly referred to as waxy cereals.
Figure 2: Changes in viscosity of a starch suspension during gelatinisation.
Source: Kent, N. L. (1975). Technology of cereals with special reference to wheat (2nd ed., p. 62). Oxford: Pergamon.
Retrogradation
During gelatinisation, the granules absorb substantial amounts of water and become swollen. The starch molecules gain kinetic energy from the heating, and become more mobile. Some of the starch breaks away from the swollen granules into the continuous phase. The relatively long amylose molecules become entangled and form a three-dimensional network, causing the increase in the viscosity of the suspension.
On cooling, the entangled amylose molecules lose their kinetic energy and motion, the water is trapped in the network, and the suspension sets to gel. If the starch gel is held for prolonged periods, crystallites begin to form at the junction zones of the network and the gel becomes increasingly rigid. This is known as retrogradation of gelatinised starch. Retrogradation means a return of the starch from a hydrated, dispersed, amorphous phase to an insoluble, aggregated or crystalline condition. Retrogradation involves mainly the crystallisation of amylose. Amylopectin retrogrades much slower. The condition is largely responsible for hardening of cooked rice, shrinkage of starch gels, and possibly staling of bread.
Recommended reading (available online at CSU library eReserve)
Daniel, J. R., & Whistler, R. L. (1985). Principal changes in starches during food processing. In T. Richardson & J. W. Finley (Eds.), Chemical changes in food during processing (pp. 305-319). Westport, Comm.: AVI.
This reading explains the processes of gelatinisation and retrogradation in more detail.
Fibre
Cellulose and hemicellulose form the bulk of the crude fibre. Both are the main components of the cell wall of cereal grain (and other plant cells). Cellulose is a polysaccharide consisting of monomeric glucose units linked together by β-(1→4) bonds. The human body lacks the cellulose-hydrolysing enzyme β-glycosidase and therefore cannot digest cellulose.
Hemicellulose is the collective name for a family of heterogeneous polysaccharides. When hemicelluloses are hydrolysed by alkaline solutions, they yield a mixture of hexoses, pentoses and uronic acids. Hemicellulose has a large capacity for water retention.
Pentosans are polysaccharides made of the pentose sugars arabinose and xylose. It is the main component of the cell wall of wheat endosperm, accounting for about 75% of the wall. Pentosans also have a high water-binding capacity.
The fibre content of the whole wheat grain is about 2%; the endosperm contains only about 0% while the bran contains about 12-14%.
Sugars
Sugars include simple sugars such as glucose, disaccharides such as sucrose, and oligosaccharides. These sugars are sometimes referred to as free sugars and can be extracted from cereals by 80% ethanol. The total sugar content of wheat is about 2%, which consists of glucose, fructose, sucrose, maltose, and certain oligosaccharides. Sugars play important roles in bread making.
Proteins
Proteins are large polymeric molecules consisting of hundreds, or even thousands of amino acids linked together by peptide bonds. The polypeptide chain is known as the primary structure of protein. Polypeptide chains of amino acids often attain certain forms of regular geometry (e. α-helix ) due to hydrogen bonding within the chains. This geometry of a polypeptide is known as the secondary structure of protein. The polypeptide chain may then fold into a globule or other configurations due to the week bonds between the side groups of the amino acids. This overall shape of a protein is known as its tertiary structure. In some protein molecules, several polypeptide chains are joined together by inter-chain bonding, frequently by disulphide bonds between cysteine residues, to give the functional protein. This is known as the quaternary structure of protein.
Distribution of protein in the grain
Protein is present in all the tissues of cereal grains. The embryo, scutellum and aleurone layers have higher levels of protein than the endosperm, pericarp and testa. About 70% of the protein in cereal is located within the endosperm. Within the endosperm, the concentration of protein decreases from the periphery to the centre. For example, in some wheat varieties, the outmost cellular layer of the
Study Guide - Module 4
Course: Food Technology (FDS308)
University: Charles Sturt University
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