Fluidized bed drying of microorganisms on carrier material

Dried microorganisms used as startercultures become more and more important for food processing and agricultural purposes. For the production of bulk-ware starter cultures, the fluidized bed drying technology was examined as an alternative process to freeze-drying yielding a product of high quality. Quality criteria for the drying process are a high survival rate of the microorganisms and little heat inactivation of intracellular enzymes. After intensive studies the fluidized bed drying of pressed yeast pellets S. Cerevisiae proved to be a suitable and economical process (1). Most of the bacteria to be dried, however, cannot be pressed into pellets without binding agents. Therefore, the drying behaviour of lactic acid bacteria sprayed onto various fluidized carrier materials was examined. Dried starter cultures produced in this way showed good mechanical flow properties and reactivation. On the other hand, the product is more hygroscopic than the pure carrier and the survival rate is o nly in the range of 20%. Simultaneous thermal inactivation trials indicated that the low survival rate is not dependent on thermal inactivation. It can be assumed that the damage of the microorganisms depends either on the microfiltration process or on osmotic effects between carrier material and bacteria.