Traditional agriculture suffers from much imponderability. Chemical synthesis seems to be an immediate alternative, but the resulting products must not carry the label ‘natural’ which, although scientifically unfounded, is preferred by the consumer. According to effective European law (EG 1334/2008) a ‘natural flavouring substance’ shall mean a

compound ‘obtained by appropriate physical, enzymatic or microbiological processes from material of vegetable, animal or microbiological origin ….’. In the US, the Code of Federal Regulation (CFR — Title 21) of the FDA contains a similar definition including the terms ‘enzymolysis’ and ‘fermentation’. Apart from the legal preference, biotechnology offers advantages especially Selleck Ribociclib for the generation of volatile flavours. Like other agonists, volatile flavours often carry stereo-centres, and both odour intensity and quality NVP-BKM120 are usually affected by the stereochemistry [1]. To execute their physiological functions, volatile flavours possess an internal clock. Not only the physical volatility, but also the chemical instability of the structures (thiol groups and aldehyde functions, tertiary alcohols, Z-double bonds, among others) limits their activity. As most bioprocesses run under ambient conditions without highly reactive chemicals in the system, volatile flavours should be among the preferred targets. More recent driving forces for a biotechnology

of flavours are the world-wide focus on a ‘greener chemistry’ and the association of certain flavours with beneficial health effects [2]. The obvious change of aroma from a fruit must to a fermented beverage are easily recognized without knowing about the (micro)biological reasons. In fact, the food industry has rediscovered fermentation as a gentle, versatile and natural means to create new products these [3].

Most of the more than 100 commercial volatile flavours from biotechnology were inspired by the empirical prototypes. Lactic acid bacteria, such as Lactococcus, Lactobacillus, Lecuconostoc, or also Enterococcus faecium (!) were grown in milk with supplements of amino acids. The headspace volatiles identified were carbonyls and esters with simple structures, but great impact on the flavour of fermented dairy products [4]. Work of such kind is still required to find facultative flavour precursors, here leucine, phenylalanine and methionine, and to derive theoretical pathways of formation. Due to their hydrophobic nature, unsaturated fatty acids are popular flavour precursors. Lactobacillus helveticus converted oleic, linoleic and linolenic acids to hexanal, octanal, nonanal, 2-octenal, 2-octanal and the corresponding alcohols [5]. Isotopes labelled precursors, such as carbon labelled linoleic acid, build the metabolic bridge from substrate to flavour product. Monoxygenase P 450 or dioxygenase genes code for the enzymes typically responsible for the formation of these volatile oxylipins. However, no such genes were ever detected in L.