Potato starch processing process potato cubes → washing → crushing → sifting → starch milk → starch meal → sedimentation → slurry → washing → bleaching → dehydration → wet starch → drying → crushing → sifting → packaging → finished product
Potatoes are one of the main raw materials for making starch in my country, especially in Northeast China and North China, which mainly use potatoes as raw materials to produce starch. Europe also produces a large amount of potato starch, and America also produces it, but not in large quantities.
1. Potato starch processing technology
Potato cubes → washing → crushing → sifting → starch milk → starch meal → sedimentation → slurry → washing → bleaching → dehydration → wet starch → drying → crushing → sifting → packaging → finished product
2. Key points of operation
1. Selection of raw materials
Raw materials for the production of potato starch should be selected with high unit yield, strong disease resistance, large potatoes, high starch content, uniform starch granule size (fast sedimentation), less soluble protein (less foam during grinding), thin skin, and few bumps ( Easy to wash), low in fiber, fresh unsprouted potatoes.
There are no special requirements for washing water, but starting from the crushing operation, all processing water should be soft water.
3. Crushing and screening
The particles of potato cubes are suspended in the cell juice of parenchyma cells, so it is easier to separate than grain starch. The greater the degree of fragmentation, the higher the flour extraction rate. Generally, the degree of fragmentation is required to be above 90%. In order to completely destroy the cell tissue, grinding is generally required. Make it 2-3 times, and sieve it with a sieve each time to remove the fibers, unground tissue and impurities in the ground material. The thing under the sieve is the powdered milk, and the thing above the sieve is put into the next grinder.
Water spraying is required during crushing and screening to facilitate grinding and washing out starch granules, which is conducive to pipeline transportation of materials. The water consumption during crushing is about 2 times the weight of the raw materials, and the water used for screening is about 4 times the weight of the raw materials. The concentration of the final dilute starch milk is about 4-7 Baume degrees.
4. Precipitation of starch granules
The starch milk obtained by sieving is an emulsion gum solution containing starch granules, crude fiber, and protein, and contains a variety of soluble sugars, organic acids and other substances, as well as microorganisms and enzymes.
The factors that affect the precipitation of potato starch include the concentration of starch milk, the size and specific gravity of starch granules and the pH value.
Starch granules precipitate faster when the starch granules are larger, have a larger specific gravity, smaller starch granule concentration, and a suitable pH value. The precipitation time needs to be completed within 8 hours, otherwise it will cause the reproduction of microorganisms and affect the quality and yield of starch. Potato starch granules are larger, and when the starch milk is thin (4-7 degrees Baume), the expected results can be obtained by using a chute. Effect. However, when the quality of the raw materials is poor, such as the potato pieces are not fully grown and partially rotten, and fermentation occurs after long-term storage or the temperature is too high during the processing season, the precipitation will be slow, resulting in a decrease in starch yield and quality. In order to accelerate precipitation, the starch milk must be adjusted. The pH value of potato juice is about 4.2-4.4, and the isoelectric point of potato protein is about pH 5.4. If the pH of starch milk is lower than 5.4, a little alkali can be added to adjust it to dehydrate and solidify the protein particles as quickly as possible. , destroy the protein glue solution and cause starch granules to precipitate.
5. Washing and bleaching
The starch obtained from the sedimentation tank of the chute is processed and diluted to 18 degrees Baume, transported to the washing tank with a pump, washed with water 2-3 times, the waste liquid is drained, and water is added to dilute to 18 degrees Baume, and the warp is delivered. Glue section.
For starch with poor raw materials and darker pink color, decolorization and bleaching should be carried out after the last washing. Use bleaching powder or SO2 as bleach.
(1) Bleaching with bleaching powder
The amount of bleaching powder used depends on the concentration of the starch milk. Generally, 100 liters of 18-degree Baume starch milk requires about 40-50g of bleaching powder.
Before bleaching, prepare a bleaching powder solution. Before use, add bleaching powder to warm water at about 30°C to prepare a 4-4.5°C Baume solution. After stirring, cover and let stand for 15 hours, then take the supernatant for use.
When bleaching, add the bleaching powder solution to the starch milk and stir continuously for 40-60 minutes. After bleaching, let it stand for about 2 hours to allow the starch to precipitate. Then drain the supernatant and repeatedly wash away the residual chlorine with water, or add a small amount of sulfur after letting it stand for precipitation. Use sodium sulfate solution to remove residual chlorine.
To test whether there is residual chlorine in the starch, a small amount of starch emulsion can be dropped into a KI solution with a concentration of 5%. It will not change color and no chlorine is present. If it turns yellow-brown, chlorine is present, KI+Cl2→KCl+I2. If residual chlorine is present, then It is necessary to add sodium thiosulfate solution to remove residual chlorine.
(2) Sulfurous acid bleaching
Sulfurous acid is a reducing agent that can inhibit oxidative discoloration and decolorize pigments. It can also change the pH value of starch milk, promote protein precipitation and inhibit fermentation. When using it, first dilute H2SO3 to a solution containing about 2.5% SO2. Each ton of raw pulp The starch milk requires about 0.6-0.8 liters of H2SO3 solution of this concentration.
After the starch milk is wrapped in cloth and dehydrated mechanically, it becomes wet starch. The appearance of wet starch is turbulent and white, agglomerated, not sour, and the cut surface is smooth.
When drying, first break the starch clumps. Natural drying takes about 3-6 days. Artificial drying. The product temperature is controlled at 40-58°C until the moisture content of the dried starch drops to 20%.
After drying, take it out and let it cool, then crush it with a pulverizer, and finally sift it through a silk sieve with a milk diameter of 0.11mm to remove small powder pieces, and then package it in cloth bags, each bag is 25 kilograms, which is the finished product.