cereal chemistry

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