Effect of the thermal level on the viability of microencapsulated living cells dehydrated by near fluidizing microwave drying

Alginate microcapsules containing cell yeasts of the species Saccharomyces cerivisae, were studied to improve the protection of cell activity during drying. Dehydration is a common operation to stabilize microencapsulated microorganisms. Here, a promising process using microwaves on a particle bed under near fluidizing conditions (NFMD) was proposed. The dehydration of microcapsules by NFMD allows performing dehydration employing lower temperatures with high survival levels of dried microorganism cells and a high quality end product. Different thermal gradients and processing temperatures of NFMD were analyzed to select the most adequate operating strategy. The obtained results were compared to those obtained by freeze-drying, assumed as reference quality drying process. The results showed that the encapsulation system, joined with the selection of favorable conditions during dehydration by NFMD, allows a post drying viability higher than 90%, with an adequate control of the process temperature. To obtain the best results regarding both, the duration of drying and quality, product temperatures of about 30 °C in the microcapsules and 5–20 °C in the air are recommended.