Due to its pleasant grapefruit-like aroma and various further interesting molecular characteristics, (+)-nootkatone represents a highly sought-after specialty chemical. (+)-Nootkatone is accumulated in its producer plants in trace amounts only, and the demand of the food, cosmetics and pharmaceutical industry is currently predominantly met by chemical syntheses. These typically require environmentally critical reagents, catalysts and solvents, and the final product must not be marketed as a "natural flavour" compound. Both the market pull and the technological push have thus inspired biotechnologists to open up more attractive routes towards natural (+)-nootkatone. The multifaceted approaches for the de novo biosynthesis or the biotransformation of the precursor (+)-valencene to (+)-nootkatone are reviewed. Whole-cell systems of bacteria, filamentous fungi and plants, cell extracts or purified enzymes have been employed. A prominent biocatalytic route is the allylic oxidation of (+)-valencene. It allows the production of natural (+)-nootkatone in high yields under mild reaction conditions. The first sequence data of (+)-valencene-converting activities have just become known.

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Novel refreshments with pleasant flavors were developed by fermentation of wort with basidiomycetes. Among 31 screened fungi, shiitake (Lentinula edodes) produced the most pleasant flavor. It was perceived as fruity, slightly sour, and plum-like. Flavor compounds were isolated by liquid-liquid extraction (LLE) and by headspace solid phase microextraction (HS-SPME). The key odor-active compounds were analyzed by a gas chromatography system equipped with a tandem mass spectrometry detector and an olfactory detection port (GC-MS/MS-O) and aroma extract dilution analysis (AEDA). For HS-SPME, a revised method of increasing the GC inlet split ratio was used. Most of the key odor-active compounds (e.g., 2-acetylpyrrole, β-damascenone, (E)-2-nonenal, and 2-phenylethanol) were detected with both extraction techniques. However, distinct differences between these two methods were observed.

As a result of their pleasant odor qualities and low odor thresholds, iso-and anteiso-fatty aldehydes represent promising candidates for applications in flavoring preparations. A novel cyanobacterial α-dioxygenase from Crocosphaera subtropica was heterologously expressed in Escherichia coli and applied for the biotechnological production of C 12 −C 15 branched-chain fatty aldehydes. The enzyme has a sequence identity of less than 40% to well-investigated α-dioxygenase from rice. Contrary to the latter, it efficiently transformed short-chained fatty acids. The kinetic parameters of α-dioxygenase toward unbranched and iso-branchedchain substrates were studied by means of an oxygen-depletion assay. The transformation products (C 12 −C 15 iso-and anteisoaldehydes) were extensively characterized, including their sensory properties. The aldehydes exhibited green-soapy, sweety odors with partial citrus-like, metallic, peppery, and savory-tallowy nuances. Moreover, the two C 14 isomers showed particularly low odor threshold values of 0.2 and 0.3 ng/L in air as determined by means of gas chromatography−olfactometry.