Top-spray fluidized bed coating: Effect of process variables on coating efficiency

The effects of several process variables on the coating efficiency of top-spray fluidized bed coating were evaluated. Sodium chloride crystals were coated with protein concentrates as a model system in a laboratory top-spray fluidized bed unit. It was established that a higher coating mass of sodium caseinate is obtained at a lower average particle size and that the highest coating mass is obtained at a critical inlet air temperature of approximately 74 degrees C. The nozzle atomization pressure was demonstrated to act as more than a droplet size influencing factor: The highest coating efficiency of sodium caseinate was achieved at a high atomization pressure, the latter having the combined effect of producing smaller droplets with a higher velocity and decreasing the bed temperature. The functional and compositional properties of protein concentrates clearly influence the coating efficiency when these products are used as a coating material in a top-spray fluid-bed process as was observed in studies using sodium, caseinate, lysozyme and blood plasma concentrate. In conclusion, coating losses may be drastically reduced by choosing appropriate processing conditions.