Sweet potato starch production methods

Fresh sweet potato starch production, there are two ways of traditional process and modern mechanical production. Traditional production process is as follows: raw material selection - washing - crushing - grinding and filtering - slurry - skimming cylinder and sitting cylinder - skimming slurry - powdering - drying.

(1) raw material selection: due to different varieties of sweet potato, its quality and starch content is also different, even if the same variety, in different places of origin, its quality is also very different. To choose a good processing starch varieties, the requirement of high starch content, sweet potato with disease is not only unsuitable for starch processing raw materials, and in storage will be infected with other potatoes, prone to rot and cause losses, so the diseased potatoes should be removed clean. (2) water washing: fresh potatoes poured into the tank with water, washing by hand, remove after washing, drain off the remaining water.

(3) crushing: after draining the fresh potatoes with a crusher into pieces, the size of the block is 2 centimeters or less, in order to facilitate the mill.

(4) grinding and filtering: this is the main link of sweet potato starch production, affecting product quality and starch output rate. Fresh potato pieces will be sent to the stone mill or macadamia mill with water grinding into potato paste, the weight of fresh potatoes and the proportion of water is 1:3-3.5. then the potato paste dumped into the aperture of 60 mesh in the sieve for filtration.

(5) to pulp: the starch milk obtained by filtration is put in a large tank, then add the proportion of acid pulp and water to adjust the acidity and concentration of starch milk. The acidity and concentration of starch milk is closely related to the precipitation of starch and protein. If the acidity of starch milk is too large, the starch and protein will precipitate at the same time, making the starch separation unclear. If the acidity is too small, the protein and starch will not be well precipitated, and the starch will be emulsion, which can not be separated. According to the production experience, the best ph value of acid pulp is 3.6-4.0. the concentration of starch milk in the vat is 3.5-4.0 boe, the amount of acid pulp is 2% of the starch milk, and the ph value of starch milk after adding acid pulp is 5.6. if the temperature is high, the fermentation is fast, and the dosage of acid pulp can be reduced accordingly.

(6) skimming and sitting tank: about 20-30 minutes after the slurry, so that the precipitation is complete, you can skim the tank. The upper layer of clear slop and protein, fiber and a small amount of starch mixture removed, leaving the bottom layer of starch. After skimming the bottom layer of starch in the tank, add water to mix, make starch milk, so that the starch precipitation again. In the process of precipitation, it is called acid pulp fermentation, which is called sitting in the tank. When sitting in the tank, the temperature and time should be controlled. Sitting temperature is about 20 degrees Celsius. When it is cold, it must be kept warm or hot water can be used when adding water to mix. Sitting tank fermentation must be hair through, in the fermentation process, appropriate stirring, to promote the completion of fermentation. General sitting time is 24 hours, hot days can be shortened accordingly. Fermentation is complete, starch precipitation.

(7) skimming and filtering: the acidic slurry generated by the sitting tank is known as the second and slurry, that is, the acidic slurry method is mainly used in the acid slurry. Fermentation of normal sour pulp has a clear flavor, pulp color white as milk. If the fermentation is insufficient or over-fermented, the color and aroma are poor, and the effect is not good when used for blending. Skimming is to skim out the upper layer of sour pulp as a pulp. The starch after skimming is sieved with a fine sieve of 120 holes. The upper part of the sieve is fine residue, which can be used as feed. The bottom of the sieve is starch, which is transferred to the small tank. After the starch is transferred to the small tank, water is added to rinse the starch, which needs to be left for about 24 hours to prevent fermentation.

(8) Powdering: after the starch settles in the small tank, the upper liquid layer is a small slurry, which can be used in conjunction with acid slurry or as water for grinding. After skimming off the small pulp, there is a layer of gray oil powder on the surface of starch, which is impure starch containing protein. Oil powder can be washed away from the surface of starch with water, and the washed out liquid can be used as nutrient material for cultivating acid slurry, and the bottom layer of starch can be taken out with a spatula, and the bottom layer of starch may be adhered by fine sand, which should be brushed away.

(9) drying: after the above process, obtain wet starch. In order to facilitate storage and transportation must be dried. Generally use sunlight drying or sent to the drying room drying.　 Mechanized production process: conveying - cleaning - crushing - sieving - desanding - precipitation (or concentration) - dehydration - drying -Air-cooled packaging.

I. The basic principle of washing

The function of washing: It is mainly to remove the mud and sand in the skin layer of sweet potato, and wash away the skin of sweet potato root. As a raw material for starch production - fresh sweet potato or dried sweet potato slices for cleaning, is to ensure that the quality of starch is the basis of cleaning, the cleaner, the better the quality of starch.

The basic principle of crushing

The role of crushing: sweet potato starch is mainly stored in the fleshy part of the tuberous roots, and only a small amount is stored in the inner skin. The purpose of disintegration is to destroy the organizational structure of sweet potato, so that the tiny starch particles can be disintegrated and separated from the tuber smoothly. The starch released from the cells is called free starch; what remains in the inner cells of the scum is called bound starch.

Crushing is one of the most important processes in the processing of fresh potatoes, it is related to the fresh potato flour rate and starch quality, crushing requirements are:

⒈ ⒈ as far as possible to make the cellular rupture of fresh potatoes, releasing more free starch particles;

Peak easy to separate. Do not want the skin residue is too fine, the skin residue is too fine is not conducive to the separation of starch and other ingredients, and increase the difficulty of separating the fine residue.

Three, the basic principle of sieving

Sweet potato pomace is a long and thin fiber, the volume is greater than starch particles, Peng rise coefficient is also greater than starch particles, specific gravity is lighter than starch particles, will be crushed to break down the original slurry, water as a medium, so that the potato pomace contains starch slurry water to further filtration.

Four, purification and precipitation of the basic principles

Mud, sand specific gravity is greater than water, and greater than the specific gravity of starch particles, according to the principle of separation of specific gravity, the use of cyclone desanding, or the use of the sedimentation method of the flow tank, can achieve a more satisfactory result. The specific gravity of yellow pulp, close to water, and lighter than the specific gravity of starch particles, its shape is palm-shaped, the longer the processing cycle, the greater the performance of the gum, sticky sieve, sticking to the starch particles, extremely difficult to separate, so the requirements of raw materials are fresh, the process is short, timely separation.

Fifth, the basic principle of dehydration

The concentrated starch slurry still contains more water, further dehydration to dry.

Sixth, the basic principle of drying

Air drying (also called rapid drying) generally used in starch factories, the whole process time is completed in a flash, so the starch granule internal water can not be pasted has been dried, so there will not be pasting or degradation of the phenomenon.

Air drying is a concurrent drying process, that is, the wet powder material and hot air flow of the concurrent process, by the heat transfer and mass transfer of two processes. When the wet starch and hot air contact, the hot air will transfer heat energy to the wet starch surface, and then from the surface to the interior, this process is the heat transfer process; at the same time, the moisture in the wet starch from the internal liquid or gaseous diffusion of the material to the starch surface, from the starch surface through the air film diffusion to the hot air, this is a mass transfer process. It is to exchange heat with high temperature airflow and wet starch in drying tube in a balanced way, so that the dried starch is in the form of powder, and it can be packed into the warehouse after cooling. The process flow is as follows: raw material pretreatment - soaking - crushing and grinding - sieving - flow tank separation - alkali, acid treatment and cleaning - centrifugal separation and drying.

The production process is as follows:

(1) Raw material pretreatment: after fresh sweet potato is harvested, it is usually cut into slices or shreds, and after sun or fire drying, it is made into dried sweet potato. This kind of dried sweet potato is inevitably mixed with various impurities during processing and transportation, so it must be pre-treated. There are two kinds of pretreatment: dry method and wet method. Dry method is to use screening equipment and wind selection equipment. Wet processing is to use the washing machine or washing drum.

(2) soaking: in order to improve the starch yield can be used alkaline water soaking. Generally saturated milk of lime or 1% dilute lye added to the soaking water, so that the ph value of 10-11. soaking time of about 12 hours, the temperature is controlled at 35-40 degrees Celsius. After soaking, the water content of sweet potato chips is 60%.

(3) crushing and grinding: after soaking, the sweet potato chips enter the hammer crusher with water to be crushed to a certain fineness, and are discharged out of the machine through the sieve holes. Dried potatoes in the crushing process, the instantaneous temperature rise, part of the starch is easy to heat paste, so that in the sieve, affecting the separation of starch and potato residue; separation in the flow tank is not easy to precipitate, resulting in an increase in the second powder, affecting the good powder output rate. In order to prevent a crushing process is easy to make starch paste, you can use two crushing, subway sieving process. That is, dried potatoes by the first crushing, sieving, and then by the second crushing process, and then sieving. In the crushing process, in order to low transient temperature rise, according to the different particle size of each channel crushing, adjust the concentration of slurry, the first channel for 3-3.5 degrees boe, the second channel for 2-2.5 degrees boe. At the same time the use of equalizer to control the amount of dried sweet potato feed, balanced slurry, to avoid overloading of the crusher phenomenon, but also conducive to the separation of the flow channel.

(4) sieve: sweet potato paste obtained after crushing the dried sweet potato, also known as liquid, must be sieved to separate out the residue, that is, fiber. Usually use flat shaking sieve, the liquid into the sieve surface, the requirement of uniform sieve, constantly dripping, starch with water through the sieve holes into the pulp pool, while the residue remains on the sieve surface from the end of the sieve discharge. The sieve cloth is 120 mesh nylon cloth. In the sieving process, due to the liquid contains pectin and other viscous substances retained in the sieve surface, affecting the separation effect of the sieve, therefore, the sieve cloth should be frequently washed to ensure that the sieve holes are smooth.

(5) flow trough separation: after fine sieve treatment of starch, generally use flow trough separation of protein. Its advantages are easy to build, less steel, save kinetic energy, operation is also more stable. Disadvantages are large area, intermittent operation, low separation efficiency, starch loss, poor labor conditions.

(6) alkali, acid treatment and cleaning: in order to further improve the purity of starch, in the process of cleaning starch, but also after alkali, acid treatment. Starch alkali, acid treatment and cleaning are carried out in the cement pool with stirring device, the size of the cement pool according to the production capacity to determine the speed of the stirrer for about 60 rpm. The starch emulsion from the flow tank is first treated with alkali treatment to remove the alkali soluble protein and pectin and other impurities in the starch. The method of alkali treatment is a degree of dilute lye, slowly added to the starch milk, control ph value of 12, while starting the stirrer, fully mixed, after half an hour, stop stirring, to be completely precipitated starch, discharge the upper layer of the waste liquid, and injected into the water clear twice, so that it is close to neutral can be. In the process of alkali treatment, you can also add sodium chlorate liquid with a concentration of 35 boe, the dosage is not more than 0.4% of the weight of dry starch. Because sodium hypochlorite is a strong oxidizing agent, with strong bleaching and bactericidal effect, so that it can achieve the purpose of whitening and antiseptic. After alkali, sodium hypochlorite treatment and cleaning, the starch is then treated with acid. Its purpose is to dissolve acid-soluble proteins, neutralize the alkaline residue of alkali treatment, and also inhibit microbial activity and reproduction. Acid treatment can be used industrial hydrochloric acid, the operation must also be added slowly, fully stirred, control the ph value of starch milk is about 3. Prevent localized over-acid, resulting in starch loss. After adding acid starch milk with alkali treatment of the same operation method to make starch precipitation, remove the upper layer of waste liquid, add water to clean, and finally make the starch is slightly acidic ph value of 6 or so, in order to facilitate the storage and transportation of starch.

(7) centrifugal separation and drying: the starch obtained after cleaning contains high moisture, it must be first dehydrated by centrifugal separator, so that the starch moisture content down to below 45%. Some factories directly as wet starch factory or use. In order to facilitate storage and transportation, the wet starch after dehydration needs to be dried to reach the required starch moisture content. Usually the moisture of sweet potato starch is 12%-13%. Starch drying can use airflow drying, because it has the advantages of fast drying speed, high efficiency, high equipment production capacity and low equipment cost.