Milling technology for cereals QA/QC on flour fortification, Kampala, 24-05-2016 DR. FI LIP VAN BOCKSTAELE FA C U LT Y O F B I O S C I E N C E E N G I N E E R I N G L A B O R ATO R Y O F C E R E A L T E C H N O L O G Y
Cereals
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Cereal grains oCeres oWhat are cereals? • Grass family (Gramineae) • One seeded fruits ◦ Caryopsis = kernel = grain ◦ Germ ◦ Endosperm ◦ Bran: seed coat and fruit coat ◦ Developes in glume (chaff, husk)
• Easy to grow, high yield, stable, storage 24/05/2016
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Cereal grains
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Cereals in the world o Annual production of major cereals in 2010/2014 (source: faostat.fao.org) 1021
844 (Million tonnes)
741 672
728
2010 2014
651
123 144
Corn 24/05/2016
Rice (paddy)
Wheat
Barley
56 68
29 28
13 17
12 15
Sorghum
Millet
Triticale
Rye
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2
Buckwheat
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Nutritional importance of cereals •Macronutrients: ◦ Carbohydrates (50-80%) ◦ Staple food ◦ Digestable: starch ◦ Undigestable: dietary fiber ◦ Proteins (8-15%) ◦ Lipids (1.5-7%)
•Micronutrients: ◦ Vitamins ◦ Minerals (1-2.5%) Dewettinck, K., Van Bockstaele F., Kühne, B., Van de Walle, D., Courtens, T. and Gellynck, X. (2008). Nutritional value of bread: influence of processing, food interaction and consumer perception. Jounal of Cereal Science, 48, 243-257. 24/05/2016
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Wheat 24/05/2016
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Source: Principles of cereal science and technology
Wheat grain ENDOSPERM (80%)
BRAN (17%) Incl. aleuronlayer
GERM (3%)
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Wheat producing countries EU 130
25
52
58 110
76
19 13 24/05/2016 (source: faostat.fao.org)
MILLING TECHNOLOGY FOR CEREALS Million tons (average 2005-2010)
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Wheat oUnique -> wheat gluten proteins -> breadmaking quality
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Wheat classification oWheat class system depends on country oWheat type •Triticum aestivum (>90%) •Triticum durum (±5%)
oCriteria (USA) •Kernel texture: hard ↔ soft •Bran color: red ↔ white •Growth habit: spring ↔ winter 24/05/2016
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Maize 24/05/2016
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Corn/Maize oMost produced grain oHighest yielding cereal (world average) • Maize: 4.3 tonnes/hectare • Paddy rice: 3.8 tonnes/hectare • Wheat: 2.7 tonnes/hectare
oAnimal feed oHuman food: tortillas, porridge oStarch production: wet milling
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http://www.baobab.net
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Maize grain
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Maize TYPES
Dent Soft
Waxy Popcorn
Sweet White 24/05/2016
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Corn producing countries
309
159
49
(source: faostat.fao.org) Million tons (average 2005-2010) 24/05/2016
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Cereal milling
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From cereal to flour oMilling: •Separation of bran/germ from endosperm •Size reduction of endosperm -> flour
oProcessing steps involved •Reception and pre-cleaning •Cleaning •Conditioning •Milling •Sieving •Blending
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Reception oReception • intake of cereals • quality control!: IN -> OUT • different factors •pre-cleaning ◦ magnet ◦ sieve cleaner ◦ aspiration 24/05/2016
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Factors affecting milling yield, end use quality o hectoliter weight o Impurities o Immature kernels
Courtesy: Marieke Dhooge
o Preharvest sprouting Sitophilus (weevil) o Insect damage
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Factors affecting food safety: moulds FUSARIUM SPP. Mycotoxins!
Courtesy: Kris Audenaert 24/05/2016
ERGOT
• Claviceps purpurea • Toxic alkaloids • Difficult to separate • 0.05% limit
Courtesy: Ingrid De MILLING TECHNOLOGY FOR CEREALS
Leyn
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Wheat grain quality control oFast analysis before grain intake: •Moisture content •Protein content •Hectoliter weight •%Impurities •Amylase activity -> Hagberg falling number •Gluten quality -> sedimentation value of Zeleny
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Storage o Storage • possible: low moisture content • BUT living substance which can decay
o Control • • • •
temperature grain condition oxygen supply moisture content grain ◦ safe value ~ cereal (13-15%) ◦ drying if necessary • pest and mould control
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Blending and cleaning oBlending • wheat mix of uniform quality • directly in storage bin • just before milling process (other tempering conditions)
oCleaning • remove impurities ◦ undesired seeds, infested kernels, shrunken and broken kernels, other foreign material
• prevent contamination of mill products + damage of equipment • separation based on differences in size, shape, specific gravity, behaviour in air currents, magnetic properties
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Cleaning DISC SEPARATOR
SCOURER MAGNET ASPIRATOR SIEVE SEPARATOR 24/05/2016
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Conditioning oConditioning = adjustment of moisture content
•not too dry ◦ bran should become elastic to avoid splintering and contamination of flour ◦ better separation of endosperm-bran ◦ less power required to grind to flour
•not too wet ◦ Endosperm too soft, no creation of sharp particles ◦ No efficient sieving
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Conditioning oTempering •controlled addition of water (and heat) •intensive mixing to ensure uniform distribution •resting for a period of time (3-36 h) ◦ optimal distribution in different parts of kernel ◦ reduce hydration differences •25°C, 15-20% moisture content ◦ Soft wheat: 15 – 16.5% ◦ Hard wheat: 17 - 18% 24/05/2016
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Milling: goals o remove bran and germ o flour with specific particle size distribution o extract as much white flour as possible 24/05/2016
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Milling o Milling process • multi-stage process • size reduction, separation (sieving) and purification operations • different materials at different stages BUT no fraction completely pure
o Milling efficiency •flour extraction degree •pureness of the fractions 24/05/2016
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Milling process Sieving in between steps
oSuccession of 3 systems:
• breaking ◦ breaks up grain in large pieces ◦ removing endosperm from bran ◦ as little flour and bran powder as possible • coarse reduction (scratching or sizing) ◦ removing small pieces of bran and embryo from endosperm ◦ smaller particles endosperm • fine reduction ◦ grinding endosperm into flour ◦ minimum in crushed germ and bran powder ◦ optimum in damaged starch granules
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Roller milling
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Roller milling: break system o 4-5 breaks, corrugated rolls • first break opens kernel • subsequent breaks: scraping endosperm from the bran • gradually smaller but more corrugations • differential from 2.5 to 1
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Roller milling: reduction system oGradual decrease of particle size into flour o Roller mill with smooth rolls, • differential 1.25 to 1 • high shear pressure, lower shear forces
oCoarse reduction: 3-5 stages • removing small pieces of bran and embryo from endosperm • smaller particles endosperm • no severe grinding: no bran in flour
oFine reduction: 6-10 stages • grinding endosperm into flour • minimum in crushed germ and bran powder • optimum in damaged starch granules o Material to purifiers, final reduction, flour 24/05/2016
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Hammer mill o impact milling o screen determines the particle size
o requires dehulling when applied for ‘white’ flour/meal
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Sieving
Purifier
Plansifter 24/05/2016
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Sieving: plansifter oSieving stage follows each set of rolls • different mill fractions • directed to: ◦ Next break rolls ◦ Reduction rolls ◦ Purifier ◦ Finished product
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Sieving oPurifiers • separation of pure endosperm and endosperm with different amounts of bran • vibrating motion of sieves: heavier endosperm close to sieve, brannier material on top • air currents fluidise and stratify according to size, specific gravity and shape
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Milling: end products Maize meal
Wheat flour
100 µm 100 µm
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Milling and flour/meal quality oParticle size oBran content -> ash content oColor oStarch damage
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Source: principles of cereal science and technology, Hoseney 24/05/2016
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Courtesy: Philip Randall 24/05/2016
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Milling technology for cereals QA/QC on flour fortification, Kampala, 24-05-2016 DR. FI LIP VAN BOCKSTAELE FA C U LT Y O F B I O S C I E N C E E N G I N E E R I N G L A B O R ATO R Y O F C E R E A L T E C H N O L O G Y