The production of maltodextrin by enzyme hydrolysis processis divided into 6 sections: raw material pretreatment, liquefaction,filtration, concentration, drying and packing.
The pretreatment consists of metering feeding,hot-water steeping,washing and removing impurities, and grinding into slurry.
Metering feeding is to ensure accurate feeding, easy to operate and manage. Steeping in hot water can make water penetrate into the internal tissue of rice, promote the expansion and softening of rice grain tissue, and facilitate washing and crushing. Washing is to remove rice bran and other impurities to ensure food hygiene and product quality. The purpose of grinding into slurry is to ensure the fineness of starch grains and the fluidity of rice slurry, to make starch easy to gelatinize, so as to create good conditions for enzyme to hydrolyze starch evenly.
The rice after steeping should be white without bran and rancidity, and the rice grains should be powdered when pinched gently with two fingers.
For the fineness of starch slurry, the percentage of granule with 60 mesh and above should be more than 80%,no coarse granule is felt, and no rice grain is left in the rice slurry.
The rice slurry concentration should be controlled between 22 and 24°Bé, the rice slurry from 1t of rice is equivalent to around 2.2m³.
The rice slurry does not ferment,and the PH is not lower than 5.2.
Generally the rice is washed mechanically,stirred and washed by compressed air in a special rice washing tank.
During washing, send the specific quantity of rice into the rice washing tank, pour in water, after the water soak the rice,inject the compressed air, wash the rice bran and impurities from the rice grains by stirring them in the water and make them friction mutually with air shock, and the suspended solids overflow from the overflow port. When there is almost no suspended solids，close the water inlet valve and air valve and let out the rice swill.Wash the rice like this two or three times repeatedly like this, and the rice can become clean.
The purpose to steep rice with hot water is to speed up water absorption and promote the softening of the rice grain tissue.
The degree of water absorption of rice grains is related to the following factors:
1).Related with the water absorption and rice grain steeping time.
Generally speaking, the steeping time cannot be less than two hours, otherwise the grain center is not steeped sufficiently which is not good for the crushing and gelatinization of the rice.
2).The water absorption degree depends on the rice quality.
The steeping time should prolong relatively for the non-waxy rice.
3).The water absorption degree is relative with the steeping water temperature.
Rising the water temperature can accelerate water absorption of rice grains and short the steeping time. In winter, the steeping water can be replaced by the cooling water, but the water temperature should not be higher than 45℃.If rise the temperature again, the rice grain surface will get gelatinized, and the starch is washed away.
In the process of steeping, we should pay attention to the rice fermentation. Although steeping for two hours will not cause fermentation due to the microorganism, if the rice bran is not washed clean,fermentation may occur, after grinding the rice into slurry,the pH may decrease during liquefaction,thus resulting in difficulty. So only after all the fermented rice grains are washed again can they be crushed.
The fermentation of rice grain and slurry usually occurs during summer and autumn with high temperature. During this period, more attention should be paid to the environmental sanitation and equipment cleaning and disinfection to reduce the chance of microbial contamination.
When grinding the rice powder into slurry, we should pay attention to the fineness and concentration.
The fineness of slurry has effect on the liquefaction degree and filtration speed.
Considering from gelatinization,the slurry with fine granularity has good solubility and is easy for gelatinization.
Considering from filtration, if the slurry is too fine,it is not good for filtration.According to the results of industrial scale production, the optimum fineness of the slurry is 70 mesh, so that both the liquefaction and filter performance are good.The rice slurry concentration is related with the fluidity and evaporation capacity of the gelatinized liquid.
Low concentration, small viscosity and good fluidity is good for gelatinization,heating and filtration. But if bringing down the liquefaction concentration, it will raise the evaporation load, not economical. The slurry with high concentration has poor fluidity and it is difficult for gelatinization. Therefore, the optimum concentration of slurry should be between 22 and 24°Bé.
Start-up: power on, no-load running first for 1 to 2 minutes, check whether there is abnormal vibration and noise, adjust the clearance between the upper and lower grinding disks until there is a slight friction noise.
Operation: Turn on the tap first,then drop rice grains, while adjusting the flow of rice and water, maintain a certain concentration of slurry.
Adjustment: Check the fineness of the slurry at any time, and gently turn the hand wheel to adjust the clearance between the grinding disks until the fineness meets the requirements. However, the finer the slurry, the greater the motor load. Therefore, the grinding disc clearance should not exceed the rated current of the motor.
Stop: After grinding the material, the residual rice grains and slurry in the hopper and grinding chamber should be washed clean with water to prevent the residual slurry from fermentation, and then turn off the power supply after the adjusting hand wheel is unwound.