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Structure and chemistry of cereals
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Cereal Chemistry and Bakery
products technology
FST 2263
Aim of the course:
•To provide the knowledge on physico-chemical
properties of cereal flours and their contribution
in attaining the specific properties of cereal based
products
•To provide the knowledge and hands-on
experience on processing of different bakery
products.
At the end of the course student will be able to;1. Describe the physico-chemical properties of cereal flour and
flour constituents2. Evaluate the functionality of cereal flour constituents in flour
based products3. Explain the principles of methods used in determining the
physicochemical properties of cereal flours and starches4. Compare the techniques of processing of bakery products5. Discuss the quality control practices applied in bakery
industry6. Practice the preparation of basic bakery products
At the end of the lesson student will be able to;
• Identify structure & composition of cereal grains
• Compare the nutrient composition and physico-chemical properties of different cereal flour
• Differentiate cereal starch according to structure
• Explain the specialty of different cereal starches
Structure & composition of cereal grains
Maize (corn),
Wheat
Rice
Barley
Oats
• Belongs to gramineae (grass) family
• Seed is commonly called as grain/ caryopsis
• Main CHO source in many nations diet
• Each cereal has unique properties which make it
suitable for a variety of food products
• Cereals require different conditions to grow.
Ex: rice - tropical climates, oats – cold temperate
Cereals
1. Wheat
•Wheat (Triticum spp.) is a grass that is cultivated temperate zone.
• The most important human food grain and ranks second in total production as a cereal crop behind maize; the third being rice
• Wheat grain is a staple food used to make flour for breads; cookies, cakes, pasta, noodles.
Common Species of wheat :-
•Triticum aestivum – Common wheat
•T. monococcum
•T. vulgare
•T. dicoccum – has certain disease resistance qualities
•Triticum compactum – Two types; white & red varieties
•T. durum/ Durum wheat/ Macaroni wheat – has a hard, translucent, light colored endosperm which makes it suitable as an ingredient for pasta
Common bread wheat can be categorized as:
• Hard / Soft varieties
• Spring / winter varieties
• White / red varieties
• Hard Red Spring — Hard, brownish, high protein wheat
used for bread and hard baked goods
- use to make bread Flour and high gluten flours
• Hard Red Winter — Hard, brownish, high protein wheat
used for bread, hard baked goods and as an adjunct in
other flours to increase protein in pastry flour
- use to prepare some brands of unbleached all-
purpose flours
Soft Red Winter — Soft, low protein wheat used for cakes, pie
crusts, biscuits.
- use to make cake flour, pastry flour, and some self-
rising flours
Hard White — Hard, light colored, opaque, chalky, medium
protein wheat planted in dry, temperate areas
- Used for bread and brewing.
Soft White — Soft, light colored, very low protein wheat grown
in temperate moist areas
- Used for pie crusts and pastry.
• Hard wheats are harder to process and red wheats may need
bleaching. So, soft and white wheats usually have higher
prices than hard and red wheats on the commodities market.
• Raw wheat seed - food ingredient called whole
wheat
• can be powdered into flour, germinated and dried
creating malt, crushed and de-branned into
cracked wheat, parboiled (or steamed), dried, or
processed into semolina, pasta
• These processed wheat are a major ingredient in
such foods as bread, breakfast cereals, crackers,
biscuits, pancakes & cakes
Structure of the wheat grain:
• Wheat grains - generally oval shaped ( range
from spherical to long, narrow and flattened
shapes)
• 5 and 9mm in length, weighs between 35 and
50mg
• Wheat grain has a crease down one side where it
was originally connected to the wheat flower.
Wheat grain, showing different sides and cross section to illustrate the depth of the crease
Pericarp Outer pericarp
Inner pericarp
Grain
Seed Seed coat (Testa)
Endosperm
Aleurone layer
Germ
Pericarp
• outer most cover
• outer pericarp consists of 3 layers
• epidermis
• hypodermis
• Inner thin walled cell
• Inner pericarp consists of
• Intermediate cells
• cross cell
•Tube cell
Seed coat
• firmly attached to the tube cells
• if these layer carries pigments, kernel is colorful
Aleurone layer
• Outer most layer of the endosperm which contains
vitamin B
Structure of the Wheat grain
The three main parts are:
1. Bran
• outer layers of the wheat grain; removed during
milling
• About 14% of the wheat kernel
• The outer coating or 'shell' of the wheat kernel is
made up of several layers
•These layers protect the main part of the kernel
• Bran is rich in B vitamins and minerals
• Wholemeal flour contains all the naturally
occurring bran.
2. Endosperm
• main part of the wheat kernel or name given to
the interior of a wheat kernel
• represents about 80% of the kernel weight
• The endosperm, once it has been ground down
to a powder, is wheat flour
• It is from this part that white flour is milled. The
endosperm is rich in energy-yielding carbohydrate
and important protein.
3. Germ (Embryo)
• part of the grain which would sprout if it was planted
as a seed
• packed with nutrients and protein with which to
nourish a new plant
• During milling the germ is usually separated from the
rest of the wheat grain ( fat content limits the shelf life
of the flour)
• The germ lies at one end of the grain and represents
only 2% of the kernel
• rich source of B vitamins, oil, vitamin E and natural
plant fat.
Chemistry of wheat grain (Per 100 g)
Rice (Oryza sativa)
•most important cereal crop in developing world
• staple food of over half the world's population
production is only slightly below that of wheat
90% is grown in southern & eastern Asian
Grain structure
consists of an outer protective covering, the hull, and the rice caryopsis or fruit
Brown rice consists of the outer layers of pericarp, seed-coat and nucellus; the germ or embryo; and the endosperm
• Endosperm consists of the subaleurone layer and starchy endosperm.
• The aleurone layer encloses the embryo
• The hull constitutes about 20 % of the rough rice weight.
•The distribution of brown rice weight:
• Pericarp 1 - 2 %
• Aleurone, nucellus, seed-coat 4 - 6%
• Germ 1 %
• Scutellum 2 %
•Endosperm 90 - 91 %
• The endosperm cells : thin-walled and packed with
starch granules
• The two outermost cell layers are rich in proteins
and lipids
• have smaller amyloplasts & starch granules than
the inner endosperm.
• starch granules are polyhedral and mainly 3 - 9 µm
in size
• Protein occurs mainly in the form of spherical
protein bodies
Chemical composition of rice grain
Hulled rice
Water 10 – 12%
Protein 5 – 9%
Fat 0.6 – 2.6%
CHO 73 – 90%
Fiber 0.2 – 1%
Ash 0.8 - 2%
Rice bran
Water 8.9 – 12.5%
Protein 10.6 – 14.8%
Fat 10.6 – 22.4%
Fiber 9.6 – 11.1%
Ash 9.3 – 15%
A. Oats (Avena sativa); B. Barley (Hordeum vulgare); C. Bread Wheat (Triticum aestivum);
D. Rye (Secale cereale).
Rye
Chemical & physical characteristics
-The rye kernel is a caryopsis.
- Caryopsis is a small dry, indehiscent, one seeded fruit.
-6 – 8 mm in length & 2 – 3 mm in width.
-The color is normally grayish yellow
-The seed consists of an embryo attach through a
scutellum to the endosperm & Aleurone layer
-The pericarp or fruit coat surrounds the whole seed
& adhere closely to it.
-A crease or furrow extends the full length of the
grain on the ventral side
-The nutritional quality of rye protein - superior to that
of other cereals because of its better balance of EAA.
-Its protein efficiency ratio seems to be higher due to;
- the greater amount of lysine present in the
water soluble proteins & the higher proportion of
globulin & albumin
-Rye lipids differ from those of most other cereals
by having a slightly greater proportion of the highly
unsaturated linolenic acid.
-Therefore susceptible to oxidation. cause rancidity
-Starch granules have a mean particle diameter greater than those of other cereals
-shape lenticular shape
spherical shape
- 8% pentosans in rye (in wheat is 3%)
- rye bread has large pores & moisture than wheat bread
-Rye has few micronutrients;
Thiamine
Nicotinic acid
Riboflavin
Pyridoxin
Pantothenic acid
Tocopherol
Oats(Avenea sativa)
-grown in cooler & moisture regions of the
temperate zones
-varieties
o red oats – heat tolerant
southern US, South America, Australia
Winter oats – planted in the late fall, latitude of 20 - 400
Spring oats – planted when the threat of frost is minimum
- used to prepare cakes, biscuits, & breakfast cereals
- The physical structure of the oat grain is similar to that of kernel of wheat & barley
- The 3 major divisions
- Bran - Endosperm - Germ
- The oat germ is larger & narrower than the germ of wheat
- Compared to other cereals oat grains are characterized by low CHO contents & higher protein & fat content
BarleyGenus: Hardeum
Most of the cultivated barley classified in to two groups
1. H. vulgare – six rowed barley
2. H. distictum – two rowed barley
Structure of Barley kernel
The caryopsis is composed of
Pericarp
Integuments
Starchy endosperm
Germ
-The outer layer of endosperm is made out of aleurone cells
-In blue barley, blue color is due to color given by the anthocynin pigments in alkaline aleurone cells
Composition of barley
Protein 12%
CHO 70%
Mineral 2%
-Low in EAA esp lysine & Methionine
-Have more lysine than corn
-Contains larger amount of vitamin compared to corn
-Barley granules Large granules(A)
Small granules(B)
Large granules(A) - contain high amylopectin
-have lower gelatinization tem
small granules(B) -contain low amylopectin
-have higher gelatinization tem
There are two major groups of protein
1.Glutelins & Prolamins
2.Albumins & globulins
Uses
1.source of malt in manufacture of alcohols, wisky, beer
2.use as a flavoring agent in breakfast cereals, malted milk, infant foods, medicinal syrups
Sorghum (Sorghum vulgare )
-Staple food in drier part of tropical Africa, china, India
-Native home is Africa
-The grains are differently colored – Yellow, Red, or Brown
Composition
Fat 3%
CHO 70%
Fiber 12%
Millets
-Common term used to large number of cultivated grasses with very small seeds
-Used as forage & as a food for both man & domestic animals
-More important in the East than West
-Generally known as poor man’s cereal
1. Fortail millets ( Setaria italica)
- Grown in Japan, China, India – grains are boiledeaten
- In North America - mainly used as a forage crop
2. Proso millet (Panicum miliaceum) – Contains 10 % proteins, 4 % Fat
- A palatable bread can be made from these
3.Finger millet (Eleusine coracana)
- Grown mainly in the tropics
- Most important cereal crop in chena in Sri Lanka
Maize (Zea mays)
-Originated in low land of tropical South America
-Leading producers : USA, China, Russia, India, Italy
Kind of maize:
Cultivars are divided in to groups, according to structure of grains
1.Pod corn — Zea mays var. tunicata
-Most primitive form
-not grown commercially
2. Popcorn — Zea mays var. everta
-Grains small with a little soft starch at the center
-When heating cause the grains to pop
3. Flint corn — Zea mays var. indurate
-Grains with hard endosperm
-A little, soft starch in the center
-Well adopted to poultry feed
4. Dent corn — Zea mays var. indentata
-Principle maize of US & North mexico
-White starch shrinks on drying to produce a characteristic dent
5. Sweetcorn — Zea mays var. saccharata
- Grain consist a glossy sweetish endosperm
- Cobs are picked immature for boiling as corn on the cobs
- Also use as a vegetable by canning or freezing
6. Flour corn — Zea mays var. amylacea
- Endosperm consists with soft starch
7. Waxy corn — Zea mays var. ceratina
- Starch is waxy & composed of entirely of amylopectin