In comparison to other manufacturing processes, such as spray drying, extrusion using the ZSK twin screw extruder provides numerous advantages. Encapsulated flavors are extruded in a highly viscous state. A time-consuming, expensive drying step – which may also damage the product – is not necessary. In addition, the temperature of the micro-encapsulation during extrusion can be controlled independently of the evaporation temperatures of solvation agents (usually water). Due to its outstanding mixing effect, the ZSK twin screw extruder ensures that the active substances are highly dispersed. The substance to be encapsulated is normally added after formation/structuring of the highly viscose envelope matrix. Furthermore, a large range of possible wall materials can be processed – in terms of the machine; there are practically no limits to the choice of matrix material.
During extrusion base material, generally a hydro-colloid or suitable powder premix with film-formation properties, is initially fed to the process section of the ZSK twin screw extruder via single as well as twin screw feeders from Coperion K-Tron. Water is added downstream as required via loss-in-weight feeders, and later the product to be encapsulated. Even at the lowest rates, the feeders operate with high accuracy and ensure the precision processing of the flavor mixtures without impairing product quality.
In the process section of the ZSK extruder, a highly viscous matrix is created from the powder-like premix together with water using melting, plasticizing, dissolving – and, if long-chain molecules are used – gelatinization. At the same time, the liquid flavor is added, distributed finely and emulsified in the matrix. At the end of the process section, the mixture is pressed through small nozzle holes and cut directly at the nozzle plate using the ZGF centric pelletizer. A clean and accurate cut is made due to the precise 3D adjustability of the pelletizer knives. This results in mechanically stable granulates with a round/oval shape and a diameter of 0.6 mm or larger, and a flavor loading of over 10%. Following outstanding product development, the best results even achieve flavor loading of up to 17%.