What are the original causes of stickiness in spray dryer drying...How to control
Source: Our Website | Date of issue:
2019-08-05 13:57:55
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Abstract: Spray-dried foods are divided into two categories: non-sticky and sticky. Non-sticky ingredients are easy to spray dry, simple dryer design and free flow of the final powder. Examples of non-sticky materials include powdered eggs, powdered milk, solut…
Spray-dried foods are divided into two categories: non-sticky and sticky. Non-sticky ingredients are easy to spray dry, simple dryer design and free flow of the final powder. Examples of non-sticky materials include powdered eggs, powdered milk, solutions and other maltodextrins, gums, and proteins. In the case of viscous foods, there is a drying problem under normal spray drying conditions. Sticky food usually sticks to the wall of the dryer, or becomes useless sticky food in the drying room and transportation system, operation problems and low product yield. Sugary and acidic foods are typical examples.
Viscosity is a phenomenon encountered during the drying process of often spraying food materials rich in sugar and acid. Powder viscosity is a cohesive adhesion property. It can be explained in terms of particle-particle viscosity (cohesion) and particle-wall viscosity (adhesion). The measure of strength combined with powder particles is due to its internal characteristic called cohesion, which forms lumps on the powder bed. Therefore, the force required to penetrate the powder agglomerates should be greater than the cohesive force. Adhesion is an interfacial property, and the powder particles adhere to the tendency of the spray drying equipment wall. The cohesion and adhesion are the key parameters for designing drying and drying conditions. The surface composition of powder particles is mainly responsible for stickiness. The cohesive force and adhesion tendency of the surface material of the powder particles are different. Because drying requires a large amount of solute to be transferred to the surface of the particle, it is in bulk. Two viscous characteristics (cohesion and adhesion) can coexist in spray-dried sugar-rich food materials. The cohesion between particles is the formation of fixed liquid bridges, moving liquid bridges, mechanical linkage between molecules and electrostatic attraction and solid bridges. The main reason for the adhesion of powder particles along the walls of the drying chamber is the loss of materials in spray-dried sugar and acid-rich foods. When the silty remains longer on the wall, it will dry and lose.
Lead to stickiness
Spray the food drying powder rich in sugar and acid to recycle the spray drying technology. Low molecular weight sugars (glucose, fructose) and organic acids (citric acid, malic acid, tartaric acid) are very challenging. Small molecules such as high water absorption, thermoplasticity, and low glass transition temperature (Tg) contribute to viscosity problems. When the spray drying temperature is higher than Tg20°C, these ingredients often form soft particles on the sticky surface, causing the powder to stick, and finally form a paste-like structure instead of a powder. The high molecular mobility of this molecule is due to its lower glass transition temperature (Tg), which leads to viscosity problems in spray dryers that are usually popular at temperature. The glass transition temperature is the main feature of the amorphous phase transition temperature. The glass transition event occurs when a hard solid, amorphous sugar undergoes a transformation into a soft rubber, liquid phase. Surface energy, solid glass has lower surface energy and does not adhere to low-energy solid surfaces. Due to the transition from the glass state to the rubber (or liquid) state, the surface of the material can be increased, and the interaction between the molecules and the solid surface starts. In the food drying operation, the product is in a liquid or adhesive state, and the liquid/adhesive food becomes a glass state due to the removal of the plastic agent (water). If the food raw material does not undergo a transition of high drying temperature than the glass transition temperature, the product will maintain high energy viscosity. If this kind of food is made of high-energy solid surfaces, it will stick or stick to it in contact.
Control stickiness
In terms of reducing viscosity, there are many materials science and process-based methods. Materials science-based methods include high-molecular-weight material liquid drying aids to increase the temperature other than the glass transition, and process-based methods include the walls and bottom of the machine room.
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