Cereal chemistry


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Structure and chemistry of cereals

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Cereal chemistry

  1. 1. Cereal Chemistry and Bakery products technology FST 2263
  2. 2. 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.
  3. 3. At the end of the course student will be able to; 1. Describe the physico-chemical properties of cereal flour and flour constituents 2. Evaluate the functionality of cereal flour constituents in flour based products 3. Explain the principles of methods used in determining the physicochemical properties of cereal flours and starches 4. Compare the techniques of processing of bakery products 5. Discuss the quality control practices applied in bakery industry 6. Practice the preparation of basic bakery products
  4. 4. At the end of the lesson student will be able to; • Identify structure & composition of cereal grains • Compare the nutrient composition and physicochemical properties of different cereal flour • Differentiate cereal starch according to structure • Explain the specialty of different cereal starches
  5. 5. Structure & composition of cereal grains Wheat Barley Rice Maize (corn), Oats
  6. 6. Cereals • 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
  7. 7. 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.
  8. 8. 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
  9. 9. 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 allpurpose flours
  10. 10. Soft Red Winter — Soft, low protein wheat used for cakes, pie crusts, biscuits. - use to make cake flour, pastry flour, and some selfrising 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.
  11. 11. • 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
  12. 12. 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.
  13. 13. Wheat grain, showing different sides and cross section to illustrate the depth of the crease
  14. 14. Pericarp Outer pericarp Inner pericarp Grain Seed Seed coat (Testa) Endosperm Aleurone layer Germ
  15. 15. 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
  16. 16. 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
  17. 17. Structure of the Wheat grain
  18. 18. 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.
  19. 19. 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.
  20. 20. 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.
  21. 21. Chemistry of wheat grain (Per 100 g)
  22. 22. 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
  23. 23. • 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 %
  24. 24. • 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
  25. 25. Chemical composition of rice grain Hulled rice Rice bran Water 10 – 12% Water Protein 5 – 9% Protein 10.6 – 14.8% Fat 0.6 – 2.6% CHO 73 – 90% Fiber 0.2 – 1% Ash 0.8 - 2% Fat Fiber Ash 8.9 – 12.5% 10.6 – 22.4% 9.6 – 11.1% 9.3 – 15%
  26. 26. A. Oats (Avena sativa); (Triticum aestivum); D. Rye (Secale cereale). B. Barley (Hordeum vulgare); C. Bread Wheat
  27. 27. 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
  28. 28. -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
  29. 29. -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
  30. 30. - 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
  31. 31. 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
  32. 32. - 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
  33. 33. Barley Genus: 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
  34. 34. -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%
  35. 35. -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
  36. 36. 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
  37. 37. 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%
  38. 38. 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
  39. 39. 1. Fortail millets ( Setaria italica) - Grown in Japan, China, India – grains are boiled eaten - 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
  40. 40. 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
  41. 41. 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
  42. 42. 5. Sweetcorn — Zea mays var. saccharata - Grain consist a glossy sweetish endosperm - Cobs are picked immature for boiling as corn on the - 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 cobs