Biotechnology of flavours--the next generation.

Volatile organic chemicals (flavours, aromas) are the sensory principles of many consumer products and govern their acceptance and market success. Flavours from microorganisms compete with the traditional agricultural sources. Screening for overproducers, elucidation of metabolic pathways and precursors and application of conventional bioengineering has resulted in a set of more than 100 commercial aroma chemicals derived via biotechnology. Various routes may lead to volatile metabolites: De novo synthesis from elementary biochemical units, degradation of larger substrates such as lipids, and functionalization of immediate flavour precursor molecules. More recently, the field was stimulated by the increasing preference of alienated consumers for products bearing the label "natural", and by the vivid discussion on healthy and "functional" food ingredients. The unmistakable call for sustainable sources and environmentally friendly production is forcing the industry to move towards a greener chemistry. Progress is expected from the toolbox of genetic engineering which is expected to help in identifying metabolic bottlenecks and in creating novel high-yielding strains. Bioengineering, in a complementary way, provides promising technical options, such as improved substrate dosage, gas-phase or two-phase reactions and in situ product recovery.