# Utilization of the Nutritional Potential of Wheat Bran Using Different Fractionation Techniques
## 5 Bran from the Standard Mill Process and Possibilities for Its Fractionation
### Electrostatic Separation  
Electrostatic separation is a \"dry method\" outside of an aqueous environment. It uses the triboelectric effect. Its manifestation in everyday life is static electricity. The method is based on the charging of particles by collisions with the device wall and subsequent separation in an electric field. The polarity and strength of the charge vary according to the material used and the temperature, pressure, or even the speed at which the material is kept. Nitrogen is often used as the carrier gas [49]. The first step is the charging of the particles entrained by the carrier gas, which occurs when the particles rub against each other or against the inner wall of the charging device. The magnitude and polarity of the resulting charge can be estimated from the so-called triboelectric series of materials, which has been developed experimentally. When two particles come into contact, the one that is higher up (at the positive end of the series) becomes positively charged. The resulting charge is greater the further apart the materials are in the series. The most commonly used material for the production of bran separation tubes is Teflon (polytetrafluoroethylene), which is located at the negative end of the triboelectric series. Other materials used to separate bran and other plant materials are nylon, aluminium, or stainless steel; unlike Teflon, these are located closer to the positive end of the triboelectric series [50; 51]. Before the actual processing of the bran by this method, the bran needs to be milled into smaller particles in order to achieve a greater number of collisions with the wall of the charging device. Nevertheless, there is a size limit below which the particles begin to adhere to the equipment wall and the number of particle collisions increases--particles that are not effective at creating a charge [52]. This phenomenon was not seen in pericarp particles, where particles of different sizes achieved the same average charge, thus the authors believe that the surface composition of these particles, in addition to their size, has an effect on the size of the charge [53]. Another fiber parameter that influences the obtained charge and thus the success of the separation is the moisture content. The best separation occurs at moisture contents below 10%, but no significant differences in separation success have been observed between moisture contents below 10% [54]. But it is possible that moisture content does not affectthe size of the recovered bran charge overall but predominantly that on the pericarp particles [55]. It has been shown experimentally that when the appropriate material is used during charging, particles originating from the aleurone layer and those originating from the pericarp acquire opposite charges and gravitate towards different electrodes, presumably due to the different cellular structure and the structure of the fiber components (branched or linear) in each outer layer [54; 56; 57]. The shape and length of the charging device then also have an impact on the success of the charging and particle separation. Cells that are spiral shaped are preferable, because they increase the delay time of the material in the cell and increase the likelihood of material colliding with the cell wall. Thus, while there is an advantage of higher particle charges at the exit when using longer devices, there is a risk of aggregation of particles with opposite charges, which then do not separate in the electric field [49]. Another parameter that can be controlled is the flow velocity of the carrier gas that carries the whole particles. A higher flow velocity is preferred, and a slightly turbulent flow is recommended for wheat bran, which increases the separation efficiency and is also capable of breaking up particle aggregates [49]. The concentration of material entering the cell also affects the success of the separation.