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Starch productionFrom Wikipedia, the free encyclopedia

Starch production is an isolation of starch from plant sources. It takes place in starch plants. Starchindustry is a part of food processing which is using starch as a starting material for production of starchderivatives, hydrolysates, dextrins.

At first, the raw material for the preparation of the starch was wheat. Currently main starch sources are:

maize (in America) – 70%,potatoes (in Europe) – 12%,wheat ­ 8%,tapioca ­ 9%,rice, sorghum and other ­ 1%.

Contents

1 Potato starch production1.1 Delivery and unloading potatoes1.2 Cleaning1.3 Rasping of tubers1.4 Potato juice separation1.5 Starch extraction1.6 Starch milk raffination1.7 Dewatering of refined starch milk and starch drying1.8 Waste products1.9 Application of potato starch

2 See also3 References

Potato starch production

The production of potato starch comprises the steps such as delivery and unloading potatoes, cleaning,rasping of tubers, potato juice separation, starch extraction, starch milk rafination, dewatering of refinedstarch milk and starch drying.

Delivery and unloading potatoes

Potatoes are delivered to the starch plants via road or rail transport. Unloading of potatoes could be donein two ways:

1. dry ­ using elevators and tippers,2. wet ­ using strong jet of water.

Cleaning

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Coarsely cleaning of potatoes takes place during the transport of potatoes to the scrubber by channel. Inaddition, before the scrubber, straw and stones separators are installed. The main cleaning is conductedin scrubber (different kinds of high specialized machines are used). The remaining stones, sludge andlight wastes are removed at this step. Water used for washing is then purified and recycled back into theprocess.

Rasping of tubers

Most often the rasping of potato tubers is carried out with a rotary grater. The purpose of this stage isdisruption of cell walls, which therefore release the starch. In practice, potato cells are not entirelydestroyed and part of the starch remains in the mash. Potato pulp rapidly turns dark, because tyrosinepresented in the potato is oxidised by polyphenol oxidase, which is located in the cellular juice.Therefore, cellular juice must be separated as soon as possible.

Potato juice separation

This allows the recovery full­value protein from juice and reduces the onerousness of water juice as asludge.

Starch extraction

After separation of potato juice the pulp is directed to the washing starch station, to isolate the starch.Most used are stream­oriented washers. In these machines pulp diluted with water is washed with astrong stream of water to flush out the milk starch. The mash smuggling with water is a waste product –dewatered potato pulp. Starch milk is contaminated by small fiber particles (potato tissue fragments) andthe remaining components of the potato juice – that’s why it is called raw starch milk.

Starch milk raffination

Raw starch milk is purified in the refining process. This involves the removal of small fibers from thestarch milk and then the removal of juice water and starch milk condensation. For this purpose, thescreens and hydrocyclones are commonly used. Hydrocyclones due to the low output (approximately 0.3cubic meter per hour) are connected in parallel and works as multihydrocyclones. For the starch milkdesanding bihydrocyclones are used. In order to prevent enzymatic darkening of potato juice thechemical refining of starch is carried out using sulfurous acid. Refined starch milk has a density of about22° Be, which is about 38% of starch.

Dewatering of refined starch milk and starch drying

It is a suspension of starch in water, which needs dewatering up to 20% of moisture. This is equivalentto the moisture content of commercial starch when stored. High temperature cannot be use in thisprocess because of the danger of starch gelatinization which destoyes granular structure. It may result insignificant changes of the functional starch properties. Therefore, removal of excess water from milkshall be done only under conditions that prevent the gelatinization of starch.

Dewatering of refined starch milk is carried out in two stages. In the first stage the excess water isremoved by means of a rotary vacuum filter. Secondly moist starch is dried, without starch pasting. Forthis purpose a pneumatic dryier is used. In this device moist starch (with water content 36 – 40%) isfloating in strong and hot (160°C) air flow and then dried during 2 – 3 seconds. Then, the starch isseparated from hot air in cyclones. Due to short time of high temperature drying and intensive waterevaporation from the starch granules, its surface is heated only to 40°C.

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Dried starch contains about 21% of water. During the pneumatic transport starch loses additional 1% ofwater.

Received starch is storing separately in silos, in jute bags (100 kg) or paper bags (50 kg). There are threekinds of starch: superior extra, superior and prima. Different sorts of starch depend on degree of purityand whiteness. The differences between them are in an acidity and content of mineral substances.

Table 1. Potato starch production characteristic.

Processing 2.000 t per 24 hoursRatio of starch extraction 87%

Water expenditure:

­ washing

­ technological

6.5m3/t

2.5m3/t

4.0m3/t

Water steam expenditure 400 – 500 kg/t starch

SO2 expenditure 0.8 kg/t potatoes

Yield: per ton of potatoes (16,8%) 175 kg starchLoss:

­ potatoes losses (transport and washing)

­ pulp starch losses

­juicy water starch losses

about 10%

0.5%

8 – 9%

1.0%

The water which is used in starch production (dirty water) for transportation and cleaning doesn’t haveto be totally clean. That’s why clarifier usage enables application of closed cycle which noticeablyreduces amount of cleaning water that is needed. On the other hand, requirements for quality oftechnological water are the same as for drinking water (microbiological and chemical contamination). Inaddition, this type of water should contain low amounts of metals such as: Ca, Mg, Fe, Mn; which hasbad influence on starch properties.

Waste products

­Potato juice ­ is a liquid waste product separated from the potatoes pulp using centrifuges or decanters.It contains about 5% of dry substance, including about 2% valuable protein, of high nutritional value,minerals, vitamins and other. In modern starch plants separation of the juice from the mash is used. Wecan get about 600 kg of coagulated protein from each 1000 kg of potatoes. The final product containsabout 80% protein (with the digestibility of about 90%), 2.5% minerals, 1.5% fat, 6% nitrogen­freesubstances and 10% water. Because of the full range of the egzogenic amino acids the formulation is avaluable protein feed.

Potato pulp is a side product of washing the starch from the mash. It contains all non­starchy substancesinsoluble in water (fragments of wall of cells) and bounded starch which cannot be mechanicallyseparated from the blended parties of potato. The pulp contains 30% of starch, which is not extracted

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because of economical reasons. That’s why the pulp is often used in animal feeding. The pulp contains alot of water and inconvenient in transportation and storage. That’s why it is really often dried anddehydrated.

Juicy water is a liquid side product obtained after refining of starch milk. It is ten times diluted potatojuice. Due to this fact, it is a sludge and it cannot be discharged to open water.

Application of potato starch

The usage of raw starch is relatively small. Starch is mainly used as material both in the manufacture offood and non­food products. In food processing a lot of starch is converted to starch hydrolysates. Alsoit is used to receive puddings, jellies, desserts, caramel and other food products. In addition, starch isprocessed to modified starch in order to change material properties. The modified starches have a widerange of applications in many industries. Applications of starch in non­food sectors include: productionof dextrin and adhesives, drilling fluids, biodegradable plastics, gypsum binders and many other. Inaddition modified starches are used as fillers, emulsion stabilizers, consistency modifiers etc. Otherimportant fields of starch application are textiles, cosmetics, pharmaceuticals and paints.

See also

Corn starch

References

Mieczysław Pałasiński, 2005. Technology of Carbohydrate Processing (in Polish). Polish Society ofFood Technologists, Małopolska Branch, Kraków, p. 63 ­ 76.

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