Principles of Bulging and Forming Preservation

Rice bran contains a large amount of lipase, and the fat in fresh rice bran can quickly decompose under the action of lipase, resulting in a significant increase in free fatty acids. In addition, factors such as high temperature, humidity, light, and air can gradually sour and deteriorate. To ensure the quality of rice bran oil products, rice bran needs to be stabilized.

Expansion, also known as structured or organized, refers to the use of the unequal distance non-standard screw system of the expansion machine to push and push the gas in the gap between the rice bran, which is quickly filled by the material. The rice bran undergoes shear action and generates reflux, increasing the pressure inside the machine chamber. With the friction between the screw and the machine chamber, the crystal of the rice bran reaches full mixing, extrusion, heating, gluing, and gelatinization, resulting in tissue changes, and the structure of the fat layer is destroyed; At the same time, mechanical energy is converted into thermal energy, and the temperature inside the chamber quickly rises to around 125 ℃, effectively passivating the activity of various enzymes in the rice bran and damaging the structure of the fat layer; When rice bran is squeezed to the outlet, the starch and protein transform into a viscous state, and the pressure instantly changes from high pressure to normal pressure, causing water to quickly evaporate from the tissue structure, forming countless microporous structures inside. After cooling and drying, the rice bran expands and forms.

Technological process

Raw material rice bran → separation of bran and Xi → conditioning → oil puffing machine → cooling → storage or to extraction plant

The rice bran from the raw material warehouse enters the cleaning screen through a lifting scraper machine, removes impurities, and enters a vertical tempering pot to adjust the temperature and moisture of the raw materials. The quenched and tempered material enters the extruder through a quantitative twisting machine, which uses a hydraulic die. The extruded material enters the counter flow flap dryer through a rotating discharge valve for drying and cooling, and the outlet moisture is maintained at 7-9% at a temperature of 50-60 ° C. The material discharged from the flap dryer passes through a scraper elevator and enters a countercurrent flap cooler for further cooling. The cooled expanded material can be stored in storage for a long time. Or directly enter the leaching workshop for leaching without undergoing deep cooling.

Preparation before expansion

Rice bran must be separated before entering the extruder. Because the raw materials contain a large amount of impurities such as broken rice and crude sugar shells, it will accelerate the wear of the extruder. More importantly, broken rice contains a large amount of starch, which prevents the rice bran from forming appropriate pressure during the expansion process. Moreover, it will loosen the structure of the expansion material and fail to achieve good expansion effect, easily increasing the powder content and residual oil of the extracted material, and affecting the diffusion effect.

The moisture content of raw rice sugar has a significant impact on the operation of the puffing machine, as it directly determines the elasticity and plasticity after puffing. The moisture content of rice bran is too high, and the elasticity of the material is poor, which cannot generate enough pressure and heat energy to properly damage oil cells and enzymes; However, if the moisture content is too low and the plasticity of the material is poor, it will cause the expansion temperature to be too high, cause the material to coking, deepen the color of the material, and easily block the expansion machine, which will not produce good expansion materials. According to the usage results, the moisture content of rice sugar before entering the machine should be controlled at 11-13%.

The temperature of the machine and the ambient temperature also have a certain impact on the puffing effect and yield. The puffing effect and yield of pre heating the raw rice sugar are better than those of pre heating the rice bran. The output of the extruder in summer is about 20% higher than in winter, due to the shorter preheating time for the extruder to reach normal operation due to the high room temperature.

Rice bran expansion

Rice bran undergoes a series of complex physical and chemical changes through the instantaneous effects of high pressure, high temperature, shear, friction, and expansion of the puffing machine. After cooling, it forms puffed particles with a diameter of approximately 3-5mm and a length of varying micropores and certain strength.

The moisture content of rice bran decreased from 11-13% before expansion to 7-9%, and the oil content correspondingly increased by 0.5-2 percentage points. During storage, the water content of puffed rice bran remained basically unchanged, and the water content increased slowly compared to raw bran.

Swelling promotes the cleavage between starch and protein molecules, resulting in gelatinization, deformation, and recombination, as well as the destruction of oil cells, leaving the oil molecules in a free state. The gelatinization temperature of rice starch is 58. A small amount of starch forms a complex with the oil released by cell rupture during the extrusion process, and the active starch and active protein produce viscosity to stick the material embryo together. The oil is fully mixed and evenly distributed. Once released from the extruder, the water in it evaporates quickly. After drying and cooling, it forms a certain compression strength and is not easy to crush Expanded rice particles without powder and with multiple microporous structures inside.

Under the instantaneous high-temperature treatment of the puffing machine, the free fatty acid content in the rice significantly decreased, and the acid value decreased by about 3mg KOH/oil. In addition, various active enzymes in the rice bran, especially lipase, lipoxygenase, lipase, and harmful bacteria, were inactivated or killed (such as bacterial lipase inactivating at 50~), effectively suppressing the rapid increase in acid value, greatly improving the quality and storage stability of the rice bran, Extend the storage period of puffed rice.

Cooling

The rice sugar that has just come out of the puffing machine, due to its high temperature, does not completely evaporate the vaporized water. It must be naturally cooled or forced cooled to become a good puffing material with certain performance and strength. If stored directly without complete cooling, it will increase the powder content of the puffed material and be prone to mold, leading to an increase in acid value.