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Potato - The Hidden Treasure

Potato is the fourth most important world food crop after wheat, rice, and maize. In five centuries, this diverse and adaptable tuber has spread from its origin in the Andes Mountains of South America to all the other continents. It was probably first taken to Europe in the mid-16th century by Spanish explorers and was introduced to Britain by English explorers sailing from the New World only a few years later. The plant was introduced in North America in 18th century and by early 19th century potato was being cultivated in the Europe too. The wake of 20th century saw the start of worldwide cultivation of potatoes.

Potato is cultivated for its tubers which are stem structures formed by the enlargement of the tips of underground stems (stolons). Potato is a perennial herb with weak trailing. Leaves are pinnate with smaller leaflets between 3 - 4 pairs of main lobes. Flowers are white, red or purple, with yellow anthers joined into a cone-like structure. The fruit is a small inedible green or yellowish tomato-like berry. Tubers are very variable in size shape and skin colour according to cultivar. Several hundred cultivars exist differing in the quality of the tubers, suitability to different climates and soil types. Freshly harvested, it contains about 80 percent water and 20 percent dry matter. About 60 to 80 percent of the dry matter is starch. On a dry weight basis, the protein content of potato is similar to that of cereals and is very high in comparison with other roots and tubers. In addition, the potato is low in fat. Potatoes are used for a variety of purposes and not only as a vegetable for cooking at home. In fact, it is likely that less than 50 percent of potatoes grown worldwide are consumed fresh. The rest are processed into potato food products and food ingredients, fed to cattle and chickens, processed into starch for industry and re-used as seed tubers for growing the next season's potato crop. The industrial processing of potato is continually increasing owing to the rise in demand of processed potato products. Figure 1 shows some of the uses of potato and potato starch.


Potato Starch & its uses: Potato starch is perhaps the most valuable derivative of potato and is considered to be a great alternative to corn or wheat starch due to its gluten free composition. It is available in powder form as well as in liquid form. Today a significant fraction of the potato industry is involved in starch production.

Potatoes yield 17 - 21% fresh weight of starch and 0.5 - 1.2% of pure protein. Potato Starch is basically a carbohydrate, consisting of two components namely amylose and amylopectin. Both these components are polymers but differ from each other in their physio-chemical characteristics as amylopectin thickens and amylose gels. The separation of these two components is energy intensive therefore the starch is modified to reduce the effect of unwanted component to meet the requirements of the application. A starch potato usually contains 80% amylopectin and 20% amylose. Most of the industrial applications require amylopectin and today the potatoes are being genetically modified to enhance the percentage of amylopectin upto 98%. 

Potato starch and its derivatives are used today in the production of paper and cardboard, pastes and glues, building materials and additives, textile auxiliaries, packaging and even for washing powders, tooth pastes, tablets, cosmetics, confectionary, food and much more. One of the most popular forms of the potato starch is the organic one and sometimes also bears the name of starch flour or potato flour.


Potato Starch Extraction Process: Starch in potatoes owes its formation to the process of Photosynthesis. The energy collected by the leaves by photosynthesis is used to make a sugar solution which is stored as grains of starch inside the potatoes. This starch needs to be extracted before being used. Fresh potatoes need to be carefully harvested, transported and stored as blows or improper storage conditions can easily damage the potatoes resulting in starch loss and perished potatoes. The most commonly used industrial process for the extraction of starch from potatoes is shown in Figure 2 and involves the following stages: 


a)    Fresh potatoes are first coarsely cleaned for removal of soil and stones. The main cleaning is done in trough washing machines where the potatoes are spinned and thoroughly washed with water. At this stage any impurities adhering to potatoes are removed.  Constant abrasion completely removes soil and most of the skin. The washing water is then pumped into clarification pools where sand, soil and stones are removed and the water is reused in the process. b)    The clean potatoes are then transferred to rasping machines where rows of saw blades are closely arranged on a drum which is rotated at high speed. Sharp saw teeth convert the potatoes into a fine mash thus opening up the tuber cells to release starch. Sulphur dioxide gas and sodium bisulphate solution are mixed with the potato gratings to avoid oxidation and stabilize the microbiological conditions in the process. c)    The pulp comprising of the coarse skin and cell fragments are separated from the rasped potatoes. This separation step is conducted by means of conical rotating sieves, the centrisieves. For better starch isolation, water is applied to the sieves through nozzles. While starch and fruit water pass through, the fibres are retained by the sieves. The pulp is drained or pressed off and used directly as feed while still damp or dried in flash dryers. The pulp is used as mix feed because of its high feed value because of its protein and residue starch content. d)    In the next step, the fruit water is separated in several steps by means of hydro-cyclone plants. Separated fruit water has a high content of proteins, amino acids, and mineral nutrients. About one half of the soluble proteins are coagulated by treatment with acid and heat and then separated in decanters. The remaining fruit water is evaporated and used for fertilizing. e)    Fresh water is introduced at this stage to raffinate the potato starch. Raffination removes the remaining impurities from the starch. f)    Refined starch milk has a dry matter content of about 35 % to 40 %. The starch is dewatered by rotary vacuum filtration to moisture contents below 40 %. The centrifugal action in filtration helps to make extraction faster. g)     Drying is conducted by means of a flash dryer. Starch must not exceed 15 % of residual moisture to be suitable for storage.


A typical schematic illustration of process flow in a potato starch extraction plant is shown in figure 3.


The World Scenario: According to FAO statistics, the global production of potatoes stood at 325.55 MMT for the year 2008 with China, India, Russia, Ukraine and USA being the top producers.  It is estimated that approximately 3.0 MMT potato starch is produced in the world annually. According to the UN trade statistics, the global exports of potato starch (HS code 110813) were 604,338 MT (US$ 341 M) for the year 2009 with Germany, Netherlands, Poland and Canada as the leading exporters. For the same period the global imports were 823,077 MT (US$ 479 M) with USA, UK, Netherlands, Chinese Taipei and Spain as leading importers.

Each year more than 9 million tons of starch is produced in EU alone, of which around 20% is extracted from potatoes. It is worthwhile to mention that potato starch production in EU is limited by quotas.


Potato Starch Market in Pakistan: Starches and their derivates are one of the major raw materials used in most of the industrial sectors in Pakistan. It is estimated that total starch and modified starches consumption of the country was approximately 240,000 tons for the year 2009 and the share of imports in the consumption was 5000 tons for the same period. According to the trademap data, 2649 tons of potato starch was imported into Pakistan in 2009.

Currently there is only one major producer of starch in Pakistan with production based on maize and is almost utilizing its full capacity. In addition, few very small companies are producing potato starch and potato flour in very small quantities. To encourage the production of starches in Pakistan, the Government of Pakistan has levied 10-20% duty on the import of starches.  


Recommendation: World over paper and board, textile and food industries prefer use of potato starch over maize, corn or wheat based starches because of its gluten free composition and other properties which include good water-uptake and swelling as well as low thermal and electrical conductivity. A growth in demand of starches in the country is being witnessed coupled with a rising trend in imports as the domestic production capacity is reaching its limits. This justifies the setting up of a potato starch extraction plant as the demand will outgrow the local production in near future.

A potato starch extraction plant will have positive effects on the potato farming in Pakistan by creating a significant increase in potato demand.  Furthermore with some minor additional capabilities installed, modified starches and other derivatives specific to certain industrial requirements, may also be produced thus adding to the profitability of the project.