Flavours and fragrances are extremely important for the food, feed, cosmetic, chemical and pharmaceutical industries. Most available flavour compounds are now produced via chemical synthesis or extraction. Drawbacks of such chemical processes are the formation of undesirable racemic mixtures and the growing aversion of the consumer towards chemicals added to his food, cosmetics and other household products. This has caused flavour companies to direct their attention towards flavour compounds of biological origin, so called natural- or bio-flavours. Up to now, plants were also an important source of essential oils and flavours: however, active components are often present in minor quantities or in bound form or are only found in exotic plants, making isolation difficult and the flavour products expensive. Apart from plant cell and tissue culture techniques (which still need further development) a directly viable alternative route for flavour synthesis is based on microbial processes, i.e. fermentation (= de novo) and bioconversion of appropriate precursor-compounds. This review presents the current state of the art of bioflavour-synthesis, based on microorganisms (bacteria, fungi, yeasts) and their enzymes, with emphasis on currently commercialised processes. It also comments on regulatory aspects of biotechnological production of aroma-compounds. A comprehensive referenced literature survey of de novo fermentation and of bioconversion processes for flavour-compound synthesis concludes this review.
