Optimization of the Convective Air Drying of Penicillium bilaii for Improved Efficiency

Abstract

Drying and preservation of Penicillium bilaii, a fungal microorganism used to promote phosphorous uptake in several crop species such as wheat, canola, and pulse crops, has been studied. A wet pellet formed from a mixture of the inoculant and a starch-based carrier was air dried to the appropriate water activity to extend the shelf life of the viable fungal spores. Convective air drying was examined as a low-energy alternative to the more expensive freeze drying technology that is currently in use. Models were developed for constant-rate and falling-rate drying periods and were compared to experimental drying studies performed with a fixed-bed, thin-layer convective dryer. The loss of spore viability during the drying process was modeled with responses to both thermal and dehydration stresses. A computer simulation has been developed that predicts both the drying kinetics and the viability loss during processing for a range of inlet air conditions. An optimization routine is applied to the simulation to determine the conditions that maximize cell viability during the process while minimizing energy requirements. This investigation demonstrates the benefit of low air flow rate on product recovery and energy conservation, and the compromise required to select the dryer operating temperature.