Drying of biotechnological products: current status and new developments.

Drying, by definition, involves removal of a liquid (generally water, but in many bioprocessing applications it could be an organic solvent or an aqueous mixture) from a solid, semi-solid, or liquid material to produce a solid product by supplying thermal energy to cause a phase change, which converts the liquid to vapor. In the exceptional case of freeze-drying, the liquid is first solidified and then sublimed. Bioproducts are produced by microbial action and are related to living organisms. Bioproducts are a subset of a broader generic definition of biomaterials which includes wood, coal, biomass, foods (biopolymers), vegetables, fruits, etc. This overview is limited to such bioproducts as whole cells (e.g., baker’s yeast, bacteria, vaccines), fermented foods (e.g., yogurt, cheese), synthetic products of both low molecular weight (e.g., amino acids, citric acid) and high molecular weight (e.g., antibiotics, xanthene), and enzymes. All of these products are characterized by their high thermal sensitivity; they are damaged or denatured and inactivated by exposure to certain TX68926.book Page 267 Monday, January 27, 2003 11:49 AM