Preparation and processing of Sweet Potato starch

Sweet potatoes can be divided into two types: fresh sweet potatoes and dried sweet potatoes. Starch produced by fresh sweet potato generally belongs to manual production in rural areas, while sweet potato starch factories mostly use dried sweet potato as starch raw material, so it belongs to industrial production.

1. Production of starch from fresh sweet potato

The technological process is as follows: raw material selection-washing-crushing-grinding and filtering-mixing-skimming and sitting-skimming-pulping-drying.

The production process is as follows:

The main results are as follows: (1) Raw material selection: due to different varieties of sweet potato, its quality and starch content are also different, even if the same variety, in different producing areas, its quality is also very different. In order to select a good variety of processed starch, high starch content is required. The diseased sweet potato is not only not suitable to be used as starch processing raw material, but also can be transmitted to other potato pieces during storage, which is easy to rot and cause loss, so it is necessary to remove the diseased potato.

(2) washing: pour the fresh potatoes into the human jar and add clean water, wash them manually, take them out after washing, and drain the remaining water.

(3) crushing: crusher for fresh potato after leaching

Break into pieces, the size of the block is less than 2 cm, in order to facilitate grinding.

(4) Grinding and filtration: this is the main link in the production of sweet potato starch, which affects the product quality and starch yield. The pieces of fresh potato are sent to stone mill or diamond mill and ground with water to make potato paste. The ratio of fresh potato weight to added water is 1:3-3.5. Then filter the potato paste in a sieve with an aperture of 60 mesh.

(5) mixing pulp: the starch milk filtered is put into a large vat, and then acid pulp and water are added in proportion to adjust the acidity and concentration of starch milk. The acidity and concentration of starch milk are closely related to the precipitation of starch and protein. If the starch lactic acid is too large, the starch and protein precipitate at the same time, so that the starch can not be separated. If the acidity is too small, the protein and starch are not well precipitated and can not be separated as an emulsion. 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 Baume, the amount of acid pulp added is 2% of that of starch milk, and the ph value of starch milk after adding acid pulp is 5.6. If the temperature is high and the fermentation is fast, the amount of acid pulp can be reduced appropriately.

(6) skimming and sitting: after the paste is exchanged, the cylinder can be left standing for about 20-30 minutes, so that the precipitation is completed. Take out the upper clear hogwash and the mixture of protein, fiber and a small amount of starch, leaving starch at the bottom. Add water to the bottom starch after skimming and mix it into starch milk to make the starch precipitate again. It plays the role of acid pulp fermentation in the process of precipitation, which is called sitting cylinder. The temperature and time should be controlled when sitting on the cylinder. The temperature of the cylinder is about 20 degrees Celsius. It must be kept warm when it is cold or hot water can be used when adding water. Sitting cylinder fermentation must be thoroughly stirred properly in the fermentation process to promote the completion of fermentation. Generally, the sitting time is 24 hours, and the hot weather can shorten some time accordingly. After fermentation, the starch precipitates.

(7) skimming filtration: the acid pulp produced by sitting in the cylinder is called two-harmony pulp, that is, the acid pulp mainly used in the acid pulp method. The normally fermented acid pulp has a clear flavor, and the pulp color is as white as milk. If the acid pulp is underfermented or overfermented, the color and flavor are poor, and the effect is not good when it is used for pulp. Skimming is the skimming of the upper acid pulp as a pulp exchange. The starch after skimming was screened with a fine sieve with a pore size of 120. The material on the sieve is fine slag, which can be used as feed. The material under the sieve is starch and transferred to the small jar. After the starch is transferred to the small tank, rinse the starch with water and place it for about 24 hours to prevent fermentation.

(8) flour: after the starch is precipitated in a small jar, the upper liquid is a small pulp, which can be used in conjunction with acid pulp or as water for grinding. After getting rid of the small pulp, there is a layer of gray oil powder on the starch surface, which is an impure starch containing protein. The oil powder can be washed away from the starch surface with water, and the washing solution can be used as a nutritional material for cultivating acid pulp. the bottom starch is taken out with a shovel, and there may be fine sand adhesion at the bottom of the starch, so it should be brushed away.

(9) drying: wet starch is obtained through the above process. It must be dried in order to facilitate storage and transportation. It is generally dried in the sun or sent to the drying room.

two。 Production of starch from dried sweet potato

The technological process 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 harvest, fresh sweet potatoes are usually cut into flakes or filaments, dried by sun or fire, and made into dried sweet potatoes. This kind of dried sweet potato is inevitably mixed with all kinds of impurities in the process of processing and transportation, so it must be pretreated. There are two kinds of pretreatment: dry method and wet method. The dry method is the use of screening equipment and air separation equipment. Wet treatment is done with a washer or bucket.

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

(3) crushing and grinding: the soaked sweet potato chips are broken into the hammer grinder with water, reach a certain fineness, and drain out of the machine through the sieve hole. In the process of crushing, the instantaneous temperature of dried potato increases, and part of the starch is easily gelatinized by heat, which affects the separation of starch and potato dregs during screening, and it is not easy to precipitate in the flow tank separation, which leads to the increase of secondary powder and affects the yield of good flour. In order to prevent starch gelatinization caused by one-time crushing treatment, the technological process of two crushing and sieving can be adopted. That is, dried potatoes are crushed in the first way, sifted, then crushed in the second way, and then screened. In the process of pulverization, in order to reduce the instantaneous temperature rise, the powder concentration is adjusted according to the different particle size of each channel, the first channel is 3-3.5 Baume degree, and the second channel is 2-2.5 Baume degree. At the same time, the material equalizer is used to control the amount of dried sweet potato, balance the pulp, avoid the overload of the crusher and facilitate the separation of the flow trough.

(4) sieving: the sweet potato paste obtained by crushing the dried sweet potato, also known as the material liquid, must be screened to separate the dregs, that is, fiber. Usually, the flat shaking screen is used, and the material liquid enters the screen surface, which requires uniform screening and continuous watering, and the starch enters the pulp storage tank with the water passing through the sieve hole, while the residue remains on the sieve surface and discharged from the sieve tail. The sieve cloth is 120 mesh nylon cloth. In the screening process, because the material liquid contains pectin and other viscous substances retained on the sieve surface, affecting the separation effect of the sieve, therefore, the sieve cloth should be washed frequently to ensure that the sieve pore is smooth.

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