Starch and starch processing

Copyright by amixon®, copying, reprinting, translation into other languages - even in part - only with the written permission of amixon GmbH, Paderborn.

In ancient times, starch was extracted from wheat and used as an additive in medicines and as glue.

This base sediment was then dried in the sun. Our ancestors later proceeded in a similar way to obtain potato starch from grated potatoes. In Europe, the starch industry developed as an ancillary trade to agriculture. The simplest devices were used, and they were only developed into special processing machines in the course of industrialisation. This improved purity, yield and cost structure.

History of starch

ca. 3500 BC

Starch is used as a glue and smoother for papyrus leaves

ca. 200 BC

Written record of a process description for obtaining starch from grain from Greece and Egypt

700 - 1300

Starch is used for colour lightening and smoothing in paper manufacturing.

1400

Starch serves as an ironing aid for stiffening garments.

1600

Starch is a base ingredient for cosmetic powder, makeup and hair dyes

1700

Starch is extracted from maize and potatoes in the USA

1770

Starch glue is used for yarn dressing

1811

Chemical modification / starch saccharification by acid catalysis

1890

In Germany, there are about 250 companies that manufacture starch

Today

In Germany, about 2600 people work in 14 factories in the starch industry. Starch production in Europe about 12 million tonnes.


Raw materials for obtaining starch in Europe are potatoes, wheat and maize, while outside Europe the starch is also extracted from field crops such as manioc and rice. Today, the commercial product starch (C6H10O5)n may contain a maximum of 3% foreign substances. In the international starch market, it has been established that the raw protein content of cereal starch may not exceed 0.58% in the dry matter, and 0.13% in potato starch.



 

average starch content in percent by weight

Amylomaize content in the starch

Wheat

60-70

20-26

Maize

62-70

0-85

Wrinkled peas

30-40

50-80

Rice

70

0-25

Barley

60-70

60-70

Potato

10-20

20-28

Gene-manipulated potato

10-20

0

Crop plants with their approximate content of starch and amylomaize

Low-protein wheat starch is extracted for dietary nutrients (e.g. coeliac disease). The Codex alimentarius (FAO/WHO Food Standards) defines starch as gluten-free if the protein content (gluten) is less than 20 mg/kg. Modern analysis methods can detect residual protein contents of less than 5 mg/kg.

Starch consists exclusively of glucose and is the actual energy source of the vast majority of plants. It is produced by photosynthesis with glucose as

n C6H12O6 – (n-1) H2O   –>    (C6H10O5)n

 Glucose                                    Starch

an intermediate stage and deposited in the plant tubers and seeds of the plants in the form of starch grains. Thousands of glucose molecules link with one another in in a helix and form a starch molecule, which in turn becomes embedded in the starch grain.

Enzymes determine the configuration and structure of the starch grains. They can form a long strand through glycosidic linkage of the glucose molecules. This structure is called amylomaize. If side chains are attached to the strand, it is called amylopectin.


The molecular similarity between the starch and cellulose molecules is interesting. Starch is the energy depot of the plants, whereas cellulose forms their cell framework – with impressively high strength and elasticity, when one thinks of wood or 4 metre- hemp stems.

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Depending on whether the anomeric OH group of the sugar A is in the α (= bottom) or β position (= top), an α-glycosidic or a β-glycosidic bond forms.

The numbers 1,4 and 1,6 indicate the respective C-atoms in the glucose molecule.

Starch is formed from the α-bond.

Every glucose molecule has different branches. These OH groups of neighbouring molecules link. Water is formed. This is how the bond between two glucose molecules is formed. Starch granulates consist of thousands of glycosidically linked glucose molecules

Cellulose is formed from the β-bond.

When opposite OH groups bond with each other, a chain of glucose monomers is formed. We find this type of the molecule in cellulose, the stabiliser of all plants.

Similarity of the molecular structure of cellulose and starch

The starch grains differ in size depending on the type of starch. The diameter of the starch particles in potatoes can be more than 100 µm, those in wheat 2 to 35 µm, those in maize 5 to 25 µm and those in amaranth only 0.5 to 3 µm. The starch grains in wheat starch are distributed bimodally (frequency distribution with two maxima). This can be used on the one hand to produce a high-purity A-wheat starch (20 – 35 µm) and on the other to produce a small-grained B-wheat starch (2 – 10 µm) with higher impurity.

 Starch normally has an amylomaize content of 14 % to 27 % and an amylopectin content of 73 % to 86 %. However, special plant breeding also produces starch types that contain up to 99 % amylopectin or up to 85 % amylomaize.

 

Amylomaize

Amylopectin

Iodine binding capacity

20%

0 bis 1%

Colour of the iodine complex

deep blue

red-violet

Solution stability

instable

stable

Thickening performance

low

high

Retrogradation; reversal of previously agglutinated starch

irreversible

reversible

Gel formation/ cross-linking

strong and fast

little and slow

Distinguishing features of the two starch components: amylomaize and amylopectin

Starch is insoluble in cold water, but the starch corns can reversibly swell slightly, increasing their volume by up to 28 %. The swelling retrogrades if water is withdrawn from the starch.

Native starch can bind water or moist goods well, but not permanently for the most part and particularly not at varying temperatures. Starch is therefore modified to accelerate, control and stabilise its gelatinisation, to stiffen fluids and stabilise their consistency irrespective of the influences of heat/cold or stirring movements.

Modified starches can exhibit hydrophilic as well as hydrophobic properties. Starch is thus adapted to the needs of the producer. In the food sector, these are in particular convenience products https://www.amixon.com/de/blog/amixon-mischer-fuer-instant-food and the dough conditioner industry with the process steps cooking, baking, roasting, shock frosting, thawing and influencing of the Maillard reactions.

Three essential types of modification can be distinguished

Physical:

  • through heat treatment, grinding, pre-gelatinisation, roller drying, extrusion or agglomeration. This treatment need not be declared for food. The inexpensive roller drying or the more expensive spray drying is used, depending on the cold solubility desired. The latter is usually combined with a fluidised bed agglomeration if the starch is to exhibit particularly good instant properties.

Chemical:

  • Starch is suspended in water in a stirred tank and, after adding a small quantity of acid or alkali, carefully heated without reaching the gelatinisation temperature. After adjusting to a specific pH value, a modifying agent is added. After neutralisation, washing, filtration and drying, the starch has completely changed properties. If starch is chemically converted, degraded, or treated with dextrin, esterified, etherified or oxidised, then it must be declared in food as an additive with an E-number or as modified starch.

  • If the crystalline structure of the starch grains is to be largely retained despite effective modification, the method of chemical cross-linking of the starch molecule groups with the help of suitable hydroxyls such as ethylene, propylene oxide or dicarboxylic acid can be used. This reduces the solubility of the starch, increases the gelatinisation temperature and, depending on the degree of cross-linking, eliminates retrogradation.

Enzymatic:

  • Enzymatic hydrolysis of starch is a highly effective process in which the starch can be saccharised to produce sweetener. Just as they can organise and bond molecular structures as well as forming molecular chains and side chains, enzymes can also split those starch molecules. As opposed to chemical splitting, enzyme-catalytic hydrolysis of starch takes place more slowly, but also at a lower temperature. The corresponding enzymes can be extracted from moulds, bacteria or the pancreas of cattle. Following the conversion, the enzymes are flushed completely from the starch derivative or deactivated. The degree of starch degradation can be set precisely so that a large number of products are available (starch syrup). This is no declaration obligation for this form of modification. Alternatively, the starch can also be split with an acid (acid hydrolysis).

  • Maltodextrin, for example for instant beverages, spice preparations, fruit preparations and ice cream, can be obtained effectively in this way. Starch is suspended in water with alpha-amylase and heated slowly while stirring slowly. There are defined stirring and dwell times at different temperatures in order to promote the most complete enzymatic splitting possible. The suspension is then washed several times, centrifuged and dried.

  • A particularly gently and effective method of contact drying takes place in the vacuum-mixer dryer from amixon®. With particularly low temperatures and a gentle circulation flow, high drying rates are achieved extremely quickly.

The integrity of a native starch is simple to establish if the starch grains are observed microscopically with polarised light. The double refraction makes native starch grains appear iridescent with a dark cross, while processed starch grains have a monochrome appearance without a cross – obviously because their crystalline structure has been destroyed.

If starch is heated as an aqueous suspension, then the starch grain is destroyed above a certain temperature, the swelling increases again and amylomaize emerges from the grain. This process is called gelatinisation. The viscosity increases, as does the clarity of the starch/water mixture and its electrical conductivity. It is a structurally viscous solution whose viscosity decreases the more the solution is stirred or sheared. In the course of cooling, the solution clarifies, the glucose chains align in parallel and form new hydrogen bonds. Depending on the type of starch, a more or less stable gel is formed.

This structurally viscous behaviour is exactly opposite to the initial state. Wet starch (water-in-starch suspension) is dilatant. The higher the shear stress, the more the viscosity increases. In special cases, drive components and mixing tools can even break or plastically deform due to the blocking effect.

Type of starch

Gelatinisation temperature [°C]

Swelling capacity (-fold)

Potato

56 - 66

1 000

Maize

75 - 80

24

Wheat

80 - 85

21

Rice

61 - 78

20

Waxy corn

63 - 72

64

The gelatinisation of starch is of great importance in various industrial applications

With a "Brabender Viscograph E" or a "Rapid Visco Analyser", you have the quality and process control technique if you wish to compare the performance characteristics of different starches with each other. A starch-water suspension is heated while constantly stirring and then cooled down again. The stirring resistance is continuously measured and plotted in an xy diagram.

Gelatinisation diagram of three different starches

Further properties of liquefied starch are texture (sliminess) and turbidity, film formation, gel formation and retrogradation. No matter where starch is used in the food industry, it should be tasteless and it should improve the end application in the interests of the consumer. Furthermore, it should positively support the mouthfeel to match the respective food.

  • a cake topping should be cold swelling and quick to prepare, support the creamy taste, but have lasting elasticity and shape stability when cutting the cake slices.

  • a spray-dried baby food should have good instant properties and a suitable liquid consistency

  • a milk-based fruit dessert or a yoghurt should feel refreshing, cooling, but by no means sticky or furry in the mouth, but on the other hand it should be easy to portion and behave drip-free in the high-performance filling machine.

  • a grill sauce should be easy to dispense from the bottle and wet the grilled food in a thick layer with high viscosity despite the effect of heat, but unfold the spice flavours in the mouth in a natural way while chewing.

  • a breadcrumb coating powdered with starch or a baking dough should cover the food evenly and adhere firmly, no matter whether the food is eaten immediately or first deep frozen, packed and stored.

  • an instant beverage powder should disperse quickly and lump-free in the liquid phase even after a long storage period
  • in a multi-stage fluidised bed process, even volatile or oxidation-prone liquids can be microencapsulated with the help of starch.


Starch gelatinisation is an endothermic process – similar to when crystals go into solution. Thus, heat must be supplied accordingly. In Germany, most types of starch are interchangeable; especially if they are used in modified form. Potato starch is usually more expensive than grain starch because the potato tubers are only available seasonally and few by-products are produced during manufacture. At the moment, the supply of wheat starch is increasing because wheat gluten in particular is becoming increasingly important as a by-product. Wheat gluten / wheat protein has always been a valued by-product that had been made available in dried form for the bakery industry or for animal fodder. Today, wheat gluten also serves as the basis for meat substitutes and has become comparatively expensive. This makes the extraction of starch from wheat increasingly interesting.

The total consumption of starch in Europe is about 12 million tonnes, with an increase of about 2% per year. In the USA, the increase is about 4%, in South America about 4.5% and in Asia as much as 7% per year. About 10% of the starch produced worldwide is used in the chemical industry, about 30% in the paper and corrugated cardboard industry, 30% in the food industry and about the same amount is modified or saccharified for the beverage and confectionery industries. The demand for starch and its derivatives is expected to continue to increase in all industrial sectors.

If the starch or starch derivative is to be brought onto the market as a powder, then the major process engineering challenges are solid-liquid separation. In the first step, this is done mechanically in horizontally rotating peeler centrifuges or vertically rotating separators. The separation takes place due to the different densities of water and solid. Then the thermal drying step follows. Convection dryers such as flow dryers, ring dryers or grinding dryers are mostly used here. The water is discharged by hot air, whereby the moist starch is pneumatically swirled and conveyed. Thermal drying is a particularly cost-intensive process step.

At this point, the amixon® vacuum mix-dryer should be mentioned briefly when it comes to the gentle drying of high-quality derivatives, such as glucose. All surfaces of the apparatus are heated. If the vacuum is adjusted to 200 mbar absolute pressure, the water already evaporates at 60 °C. The thermal stress is therefore extremely low. The vertical design has many advantages, such as particularly good complete discharge and particularly gentle flow of the goods at low rotational speeds.


https://youtu.be/gVzx8jOgFF0  and https://youtu.be/FavGACava3M


The food industry is a major driver for the application and further development of starch derivatives

  • as additives for instant foods 
  • as a for tablet filler for food supplements
  • as a viscosity adjuster and turbidity additive for instant beverages
  • for increasing the creaminess in dessert production
  • for the conditioning of sauces for frozen instant meals
  • as a base compound for oleoresins in flavour and spice refinement
  • to increase the water binding capacity in sausage and meat processing
  • as a binding agent in commercial kitchens and canteens
  • as a filler for flavour enhancers
  • as an additive to sugar for coating the particles with fat
  • as an additive for flour treatment agents and ready-to-bake flours
  • as a conditioning agent for breadcrumb coatings

As multifaceted as is the use of starch and its derivatives in the food industry, it is also used in the pharmaceutical industry.

  • as a lubricating powder for medical gloves
  • as a filler to make tablets a practical size
  • as coating and disintegrant for tablets
  • as a base compound for medical powders and deodorants
  • as a carrier to adhere medical active ingredients
  • to dilute cosmetic rouge
  • as a release agent and lubricant to make tablet presses work trouble-free
  • as a powdering compound to permanently separate sticky particles from each other
  • as viscosity adjuster for creams, emulsions, ointments and even aerosols

A wide variety of starch derivatives is also used in the process and heavy industries.

For example

  • for the production of flocculants and foam suppressors for water treatment
  • in the production of cooling lubricants for tunnel and earth drilling
  • to adjust the fluidity of concrete for concrete pumps
  • for the conditioning of mould sands in the foundry industry
  • for smoothing cotton threads to allow wear-free weaving in textile production
  • as an adhesive for postage stamps and corrugated cardboard
  • for the production of wood glues

In the vast majority of cases, starches and starch derivatives in powdery form are irreplaceable additives for the production of powder mixtures for the above products. The mixer determines the process. It must produce an ideal mixing quality in a short time - without heating the mixture - which cannot be improved in practice. This process is made more difficult when liquid additives are involved in the recipes, which is usually the case. Starches and their derivatives are usually very finely dispersed, dusty, swelling and poorly flowing. As products of organic origin, they are also moderately to particularly prone to dust explosions. Often, they have the tendency to adhere to the mixing tools and to the walls of the mixing chamber.

If starch and starch derivatives are used as carriers for liquid aromas, oleoresins, food dyes, baking extracts, oils and fats, it requires great experience to quickly and homogeneously bring about liquid residue-free wetting, because the most important goal must be that the energy input is as low as possible. The colder the overall mixture leaves the mixing plant, the better the later filling, storage, quality preservation and freshness consistency will work. The preparation of aroma and flavour, instant food, soups, dips and sauces is often a multi-step operation. Specific coating effects are intended to enclose and protect the liquid active ingredients. There is a major conflict of objectives to obtain the highest possible liquid material loading on the one hand and the best possible flowability of the finished mixtures on the other.

It is undisputed that amixon GmbH is a trendsetter for new process engineering and hygiene standards. In this respect, the mixing results of almost all other mixer types can be reproduced and usually also improved. New processes often have to be established as part of product developments. amixon GmbH has ideally designed precision mixers for pilot projects.

These have vertically mounted helical mixing tools and can be used with a wide variety of filling levels. After a few revolutions, the helix of the mixing device produces ideal homogeneity for almost all types of dry, moist and wet solids and pastes. amixon® mixers are established worldwide and are known for their particularly hygienic design and a complete discharge of up to 99.98%. Large inspection doors are manufactured using to the Clever-Cut® and OmgaSeal® process. They seal permanently, absolutely gastight and free of dead space and allow both manual dry cleaning and automatic wet cleaning; fast and thorough drying is particularly important. In the amixon® technical centre, more than 30 different vertical helix mixers are available with batch sizes from 10 litres to 2000 litres. A test day in the amixon® technical centre provides those carrying out the tests with high knowledge gains and first-class test results, which can be transferred to a wide variety of sizes.

amixon® KoneSlid® mixer for particularly effective wetting processes - © by amixon GmbH

All components of the amixon® mixers originate from the in-house production in Paderborn, where they are produced with a high degree of automation under a regime of effective make-to-order production.

Author:
Ludger Hilleke, Member of the Management Board of amixon GmbH


Copyright by amixon®, copying, reprinting, translation into other languages - even in part - only with the written permission of amixon GmbH, Paderborn.