Application of Biotechnology to the Production of Natural Flavor and Fragrance Chemicals

During the past years biocatalytic production of fine chemicals has been expanding rapidly. Flavors and fragrances belong to many different structural classes and therefore represent a challenging target for academic and industrial research. Here, we present a condensed overview of the potential offered by biocatalysts for the synthesis of natural and natural-identical odorants including flavors and fragrances, highlighting relevant biotransformations using microorganisms and isolated enzymes. The industrial processes based on biocatalytic methods are discussed in terms of their advantages over classical chemical synthesis and extraction from natural sources. Recent applications of the biocatalytic approach to the preparation of the most important fine odorants are comprehensively covered. Flavors and fragrances are extremely important for the food, feed, cosmetic, chemical and pharmaceutical industries. Most available flavor 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 flavor companies to direct their attention towards flavor compounds of biological origin, so called natural or bio-flavors. Up to now, plants were also an important source of natural flavor and fragrances represented by their essential oils However, active components are often present in minor quantities or in bound form which make their isolation not economic or difficult leading to expensive flavor or fragrance compounds. Apart from plant cell and tissue culture techniques a directly viable alternative route for flavor 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 bioflavor-synthesis, based on microorganisms (bacteria, fungi, yeasts) and their enzymes, with emphasis on currently commercialized processes. It also comments on regulatory aspects of biotechnological production of aromacompounds such as the advances in solid state fermentation, the bioreactors used for the production. A comprehensive referenced literature survey of de novo fermentation and of bioconversion processes for flavor-compound synthesis and recovery of volatile compounds and the modeling approaches used for the theoretical study of transfer in these processes concludes this review.