สมาคมแป้งมันสำปะหลังไทย Thai Tapioca Starch Association
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Manufacturing Process Development in Thai Cassava Starch Industry

Introduction
Cassava (Man/hot esculenta Crantz) is one of the most important commercial crops in Thailand. It is known as cassava or tapioca. Thailand is a major producer of cassava, with an annual yield of 16-18 million tons, accounted for about 10 percent of global production. Approximately 40 percent of the cassava produced in Thailand is processed into cassava starch, for which the domestic demand is as high as 1.3-1.7 million tons per year.

The technology development of for cassava starch processing can be divided into three phases. The first phase is the production of cassava flour. It is processed from fresh roots using simple techniques like sedimentation. The wet flour is dried by baking on a hot surface. The second phase is the production of cassava starch using more sophisticated techniques based on centrifugal force for starch separation and dewatering. The resulting moist starch is dried in a flash drier. Currentiy, there are 48 factories registered as members of the Thai Tapioca Starch Industries Trade Association, All of these factories use the centrifugal technique and flash drier in their starch processing plants, The starch obtained from this process is highly pure and regarded as top-quality starch. The third phase of technology development involves environmental concerns and safety issues. Clean technology or Zero Discharge System has been implemented, This inciudes issues like energy and waste management (e.g. biogas production). The principles of GMP (Good Manufacturing Practices) and HACCP (Hazard Analysis and Critical Control Points) have also been incorporated. In addition, the manufacturing process has been developed into ISO 9000 standards.
All cassava starch factories in Thailand use the processing technology of the second phase and are currently in the transitional stage to develop into the third phase. Based on the production capacity, manufacturing plants can be divided into
a) Large-sized factories with the production capacity over 200 tons per day
b) Medium-sized factories with the production capacity of 100-200 tons per day
c) small-sized factories with the production capacity of 100 tons or less per day.

Cassava Starch Manufacturing Process
Equipment and process of cassava starch production

1 Raw Material Preparation

As soon as cassava roots arrive at a processing plant, the factory's representative randomly takes likes samples of the roots to determine their starch content. This is necessary since the purchase price is set on the basis of starch content. The roots are first piled up on the ground, then put into a hopper, and transferred to a conveying belt where the woody ends of the roots are cut off by workers. The roots are then passed to a sieve to separate loose peels, sand and any adhering dirt.

After the roots are washed in a root washer. The number or length of the washer depends on the production efficiency of a factory. Washing water from a washer containing some loose peels, is passed to a rotary screen a perforate cylindrical tank with a spiral part driving the retained loose peel to an outlet. Water passing through the screen then enters the wastewater treatment system.

One of the most important factors in the development of starch production is the management of raw material. The quality of cassava roots has a significant effect on the quality of the final product. As soon as the roots are harvested, they must be immediately transported to a factory. Factories need to improve the storage conditions such as providing storage area with roof and improve an inventory system for cassava roots like using a first-in, first-out system. The detailed information about the roots such as varieties, the age of harvested roots, starch content, and planting location needs to be recorded. It has been clearly shown that these factors greatly affect the quality of the starch product.

2 Rasping of Cassava Roots

Washed roots are transported via conveyor belt to a root chopper. Inside this machine, the cassava roots are chopped into smaller pieces with large cutting blades. The chopped roots are then taken to a rasper, a drum aligned horizontally on its surface, rotating at about l,OOO rpm. The drum is approximately 77.5 cm. in diameter, equipped with 144 blades, which are 30 cm. in length. During rasping, water is used to facilitate the process. The resulting suspension (rasped fresh pulp) consists of starch, water, fiber, and other impurities.

In general, a small rasper drum, with a high number of blades per surface area, is used with rather low speed to avoid such a fine pulp that may create difficulty in starch extraction which could lead to low production efficiency. Recent development has led to a larger rasping drum with fewer blades (about 80-83) able to run at a higher speed (about 1,450-2,000 rpm), which results in higher production efficiency.

3 Starch Extraction

The extraction of starch starts by pumping the rasped fresh pulp into a decanter, a cylinder with conical ends separates the water containing protein and fat from the extracted using centrifugal force. The decanter rotates at a speed of 3,000 rpm. It is usually the first step after the rasper. However, the pulp is sometimes fed directly into an extractor since decanter is not installed in all factories.

The extractor, used to separate starch slurry from the fiber and pulp, is a cone-shaped perforated stainless steel basket constantly spinning at 600-800 rpm. The starch granules are small enough to pass through the pores of the perforated basket into an outer tank, Larger pulp particles, retained inside the basket, and are discharged at the upper outlet. Water is constantly applied to the machine to facilitate starch extraction. There are two types of extractors: a coarse extractor with a perforated basket of 35-40 mesh and a fine extractor with a filter cloth of 100-120 mesh or 140-200 mesh placed on the perforated basket. An aqueous solution of sulfur dioxide is used in the fine extractor to prevent the formation of slimy film that could clog the filter cloth. This also prevents loss of starch by microorganisms and helps In bleaching of the starch. The use of sulfur dioxide solution is very important to the extraction process. Different amounts of sulfur dioxide used result in different qualities of starch. The starch slurry is passed to the coarse extractor first to separate a coarse pulp, and then passed to a fine extractor to separate fine pulp. The coarse and fine pulp is then passed to a pulp extractor and pressed into dry pulp with a screw press. Extractors are generally used in sets arranged in two lines with a trough between them to receive the discharged from the extractors. One factory has 4-6 sets, with 6-12 machines per set.

Recently, new technology for starch extraction and pulp pressing has been developed, A vibrating screener is used instead of a fine extractor. It is a rectangular screen of 150-250 mesh that vibrates constantly. This is more efficient than a fine extractor. In some factories, belt presses have been used in place of screw presses. This is a belt moving on rollers to squeeze water out of the wet pulp. A blade is located at the end of the belt to scrapes the pulp off. The resulting pulp contains lower moisture content than that obtained from a screw press. The belt press supports the processing plant with large raspers operating at higher speeds.

The starch slurry from fine extractors is purified and concentrated in a separator. Generally, a 2-phase nozzle type separation machine is used. This method utilizes centrifugal force created by rotating the machine at about 3,000 rpm. The liquid that enters the machine is separated into two phases: concentrated starch slurry and clear water with impurities (mostly used to wash the roots). Factories usually use two sets of separators. The final starch slurry obtained is held at 18-20oBe as it enters the dewatering process. Many factories have installed three sets of separators so that starch slurry leaves the separators with a constantly high concentration.

To improve the separation process, a 3-phase nozzle type separation machine has been developed. This uses the same principles as the 2-phase machine, but the liquid is separated into three phases: the heavy phase, the medium phase, and the light phase. The medium phase liquid contains small starch granules and fine pulp. It can be reused in the process but fine pulp has to be removed first. The light-phase liquid has less impurities and can be reused. The 3-phase machine uses a less water and reduces the number of steps in separating the starch. In the use of a hydrocyclone to facilitate the separation of impurities and chemicals from starch slurry and the installation of a densitometer to measure the concentration of starch slurry are also necessary to obtain starch slurry and starch product with consistent quality.

The starch slurry from the separators is pumped to a dewatering centrifuge. With filter cloth placed inside it, rotates at about 1,000 rpm to remove water from the starch slurry. Some factories use high quality filter cloth to prevent loss of starch granules through the filter, The resulting starch cake, scraped off the machine by workers, has a moisture content of 35-40 percent, It starch cake is then taken to the drying unit. Presently, larger and automatic dewatering centrifuges are being used. Other dewatering systems have been tested. It has been shown that high pressure filtration greatly reduced moisture content of the starch cake. The resulting filtrate also has low solid content.

4 Drying Process

Cassava starch is dried using a pneumatic conveying dryer, A burner is generally used to generate heat. There are two types of burners in use today: hot air burners and thermo-oil boilers. Air, heated to 170 to 200?C, is used to dry the starch cake in a flash dryer. The starch is transferred to a drying cyclone and then a cooling cyclone. The dried starch is then sifted to assure uniform particles. The sifted starch is normally packaged in small bags of 20, 30 and 50 kilograms. Jumbo bags holding 500 and 1,000 kilograms are also used.

The direction for development of drying technologies is to reduce energy costs associated with drying the starch, This includes the production of biogas from the wastewater, which is very suitable because biogas can be used to generate energy in the production process (accounted for about 75% of required energy). The number of years required for a return on investment can be estimated.

5 Packaging and Storage
Since dried starch contains low moisture content of 9-11 percent and low density, a lot of dust is generated during packaging. If the storage of starch is available prior to packaging, its moisture content will come close to equilibrium with the atmosphere and there will be less dust generated during packaging. The packages bags are placed on pallets, with stacks of more than four or five meters being avoided. The packaged starch is stored and distributed based on a first-in, first-out system.


There are many factors that significantly affect the quality and physicochemical properties of the starch during storage including temperature, relative humidity, and storage time. When stored in areas of high relative humidity, the starch absorbs greater amount of moisture, As a result. the bulk swelling power of the starch decreases. Conversely, starch stored in areas of low relative humidity has lower moisture content. As a result. It has a greater water uptake and a higher bulk swelling power. Besides, storage in high relative humidity areas for a long period of time causes the starch to deteriorate due to microorganisms and biochemical reactions, Numfor et 01. (1995) reported that swelling power and percentage of solubility of cassava starch decreased as the degree of microbial contamination increased, The amount of sulfur dioxide also greatly affects the quality of cassava starch during storage. It has been shown that viscosity of starch with high amount of sulfur dioxide decreases faster than that of starch with lower amount of sulfur dioxide

Water and Energy Consumption

1 Ener gy System
Both electrical and heat energy are needed in the production of cassava starch, Energetics (Australia) pty., Ltd. (1996), commissioned by the National Energy Policy Office, conducted a study on the energy consumption in cassava starch factories and summarized the distribution of energy usage as shown. The study also suggested that the operators could reduced the energy cost if they had a better understanding about demand charges, peak periods, and energy charges. For instance, a timer installation to stop water pumps during peak periods could greatly reduce their electricity expenses. According to a report by the Faculty of Engineering, Chiang Mai University (1996), the production of cassava starch consumes about 75 percent of energy from petroleum fuel and 25 percent from electricity. The total energy required to produce one kilogram of starch is 2.125 MJ.

2 Water System

Water is considered such an important raw material as cassava roots, since most factories are located in the Northeast area, where water is scarce. The production process requires as high as 10 to 30 cubic meters of water per ton of starch. The quality of water is thus often being considered less important than its volume. How ever, the quality of water directly affects ash content, color, and other quality of the starch produced. The best way to use water in the process is to keep water quality at the consistent level and use as little water as possible without affecting the quality of the starch.

Environment

Environmental problems resulting from the cassava starch industry are caused by waste from the processing plants. Some solid waste like roots corky skin or bark is currently used In the cultivation of mushroom. However, the major part of solid waste namely cassava pulp has not been fully utilized. Due to its high moisture (60-70 percent) and starch contents (50 percent of dry weight), cassava pulp is a rich source for microorganisms and creates foul-smelling gasses that disturb local residents, A mixture of pectinase and cellulase has been employed to improve the efficiency of starch extraction from the
cassava pulp, The resulting pulp has less starch content and is easily dried, facilitating its further utilization.

Wastewater management is an issue that must urgently be addressed. Most existing natural pond system used in the factories requires large areas, Besides, fermentation in these open-ponds creates a foul smell disturbing local residents. The production of biogas should be developed in the wastewater treatment process as a source of heat energy for drying starch,


Source :
Sittichoke Wenlapatit
Cassava and Starch Technology Research Unit. Kasetsart University
[National Science and Technology Development Agency.
Ministry of Science. Technology and Energy )
Klanarong Sriroth
Department of Biotechnology. Faculty of Agro-Industry. Kasetsart University
aapkrs@nontri.ku.ac.th
  Thai Tapioca Starch Association (TTSA)
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Tel : +66-2285-4282 to 85  Fax: +66-2285-2807

Email:Contact@ThaiTapiocaStarch.org
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Tapioca Starch
Price as of

16 Dec. 2014


FOB Price
@ USD 430/MT
Notes :
   1. Including 50 Kg. Bag, PP/PE bag.
   2. Delivery to Bangkok port.

Domestic Price
@ 13.30  THB/Kg.
Notes :
   1. Packaging and VAT not included.
   2. Super premium grade starch.

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